Python is a very simple yet very powerful object oriented programming language.

Python is developed by Guido van Rossum. Guido van Rossum started implementing Python in 1989. Python is a very simple programming language so even if you are new to programming, you can learn python without facing any issues.

Interesting fact: Python is named after the comedy television show Monty Python’s Flying Circus. It is not named after the Python snake.

Features of Python programming language

1.Readable: Python is a very readable language.

2.Easy to Learn: Learning python is easy as this is a expressive and high level programming language, which means it is easy to understand the language and thus easy to learn.

3.Cross platform: Python is available and can run on various operating systems such as Mac, Windows, Linux, Unix etc. This makes it a cross platform and portable language.

4.Open Source: Python is a open source programming language.

5.Large standard library: Python comes with a large standard library that has some handy codes and functions which we can use while writing code in Python.

6.Free: Python is free to download and use. This means you can download it for free and use it in your application. . Python is an example of a FLOSS (Free/Libre Open Source Software), which means you can freely distribute copies of this software, read its source code and modify it.

7.Supports exception handling: If you are new, you may wonder what is an exception? An exception is an event that can occur during program exception and can disrupt the normal flow of program. Python supports exception handling which means we can write less error prone code and can test various scenarios that can cause an exception later on.

8.Advanced features: Supports generators and list comprehensions. We will cover these features later.

9.Automatic memory management: Python supports automatic memory management which means the memory is cleared and freed automatically. You do not have to bother clearing the memory.

What Can You Do with Python?

You may be wondering what all are the applications of Python. There are so many applications of Python, here are some of the them.
1. Web development – Web framework like Django and Flask are based on Python. They help you write server side code which helps you manage database, write backend programming logic, mapping urls etc.

2. Machine learning – There are many machine learning applications written in Python. Machine learning is a way to write a logic so that a machine can learn and solve a particular problem on its own. For example, products recommendation in websites like Amazon, Flipkart, eBay etc. is a machine learning algorithm that recognises user’s interest. Face recognition and Voice recognition in your phone is another example of machine learning.

3. Data Analysis – Data analysis and data visualisation in form of charts can also be developed using Python.

4. Scripting – Scripting is writing small programs to automate simple tasks such as sending automated response emails etc. Such type of applications can also be written in Python programming language.

5. Game development – You can develop games using Python.

6. You can develop Embedded applications in Python.

7. Desktop applications – You can develop desktop application in Python using library like TKinter or QT.

How to install Python

Python installation is pretty simple, you can install it on any operating system such as Windows, Mac OS X, Ubuntu etc. Just follow the steps.

You can install Python on any operating system such as Windows, Mac OS X, Linux/Unix and others.
To install the Python on your operating system, go to this link: https://www.python.org/downloads/. You will see a screen like this.
Python Downloads

I would recommend you to download the latest version of Python 3

Comments in Python Programming

A comment is text that doesn’t affect the outcome of a code, it is just a piece of text to let someone know what you have done in a program or what is being done in a block of code. This is especially helpful when someone else has written a code and you are analysing it for bug fixing or making a change in logic, by reading a comment you can understand the purpose of code much faster then by just going through the actual code.
Lets see how a comment looks like in Python.

# This is just a text, it won't be executed.

print("Python comment example")

Types of Comments in Python

There are two types of comments in Python.
1. Single line comment
2. Multiple line comment

Single line comment

In python we use # special character to start the comment. Lets take few examples to understand the usage.
# This is just a comment. Anything written here is ignored by Python

Multi-line comment:

To have a multi-line comment in Python, we use triple single quotes at the beginning and at the end of the comment, as shown below.
''' This is a multi-line comment '''

Python Comments Example

In this Python program we are seeing three types of comments. Single line comment, multi-line comment and the comment that is starting in the same line after the code.

''' We are writing a simple program here First print statement. This is a multiple line comment. '''

print("Hello Guys")

# Second print statement

print("How are You all?")

print("Welcome to BeginnersBook") # Third print statement

# character inside quotes

When # character is encountered inside quotes, it is not considered as comment. For example:

print("#this is not a comment")

Output:

#this is not a comment

Python Variables with examples

Variables are used to store data, they take memory space based on the type of value we assigning to them. Creating variables in Python is simple, you just have write the variable name on the left side of = and the value on the right side, as shown below. You do not have to explicitly mention the type of the variable, python infer the type based on the value we are assigning.

num = 100      #num is of type int
str = "Chaitanya"      #str is of type string

Variable name – Identifiers

Variable name is known as identifier. There are few rules that you have to follow while naming the variables in Python.
1. The name of the variable must always start with either a letter or an underscore (_). For example: _str, str, num, _num are all valid name for the variables.
2. The name of the variable cannot start with a number. For example: 9num is not a valid variable name.
3. The name of the variable cannot have special characters such as %, $, # etc, they can only have alphanumeric characters and underscore (A to Z, a to z, 0-9 or _ ).
4. Variable name is case sensitive in Python which means num and NUM are two different variables in python.

Python Variable Example

num = 100

str = "BeginnersBook"

print(num)

print(str)

Python multiple assignment

We can assign multiple variables in a single statement like this in Python.

x = y = z = 99
print(x)
print(y)
print(z)

Output:

99
99
99

Another example of multiple assignment

a, b, c = 5, 6, 7
print(a)
print(b)
print(c)

Plus and concatenation operation on the variables

x = 10
y = 20
print(x + y)

p = "Hello"
q = "World"
print(p + " " + q)

Data Types

A data type defines the type of data, for example 123 is an integer data while “hello” is a String type of data. The data types in Python are divided in two categories:
1. Immutable data types – Values cannot be changed.
2. Mutable data types – Values can be changed
Immutable data types in Python are:
1. Numbers
2. String
3. Tuple
Mutable data types in Python are:
1. List
2. Dictionaries
3. Sets

Python Keywords and Identifiers with examples

A python keyword is a reserved word which you can’t use as a name of your variable, class, function etc. These keywords have a special meaning and they are used for special purposes in Python programming language. For example – Python keyword “while” is used for while loop thus you can’t name a variable with the name “while” else it may cause compilation error.

There are total 33 keywords in Python 3.6. To get the keywords list on your operating system, open command prompt (terminal on Mac OS) and type “Python” and hit enter. After that type help() and hit enter. Type keywords to get the list of the keywords for the current python version running on your operating system.


Welcome to Python 3.6's help utility!
...
help> keywords

Here is a list of the Python keywords.  Enter any keyword to get more help.

False               def                 if                  raise
None                del                 import              return
True                elif                in                  try
and                 else                is                  while
as                  except              lambda              with
assert              finally             nonlocal            yield
break               for                 not                 
class               from                or                  
continue            global              pass

Example of Python keyword

In the following example we are using while keyword to create a loop for displaying the values of variables num as long as they are greater than 5.

num = 10
while num>5:
    print(num)
    num -= 1

Python Identifiers

In the last article, we discussed about variables in Python.
Variable name is known as identifier. There are few rules that you have to follow while naming the variables in Python.
For example here the variable is of integer type that holds the value 10. The name of the variable, which is num is called identifier.

num = 10

1. The name of the variable must always start with either a letter or an underscore (_). For example: _str, str, num, _num are all valid name for the variables.
2. The name of the variable cannot start with a number. For example: 9num is not a valid variable name.
3. The name of the variable cannot have special characters such as %, $, # etc, they can only have alphanumeric characters and underscore (A to Z, a to z, 0-9 or _ ).
4. Variable name is case sensitive in Python which means num and NUM are two different variables in python.

Python identifier example

In the following example we have three variables. The name of the variables num, _x and a_b are the identifiers.

# few examples of identifiers

num = 10
print(num)

_x = 100
print(_x)

a_b = 99
print(a_b)

Python Data Types

Data type defines the type of the variable, whether it is an integer variable, string variable, tuple, dictionary, list etc. In this guide, you will learn about the data types and their usage in Python.

Python data types

Python data types are divided in two categories, mutable data types and immutable data types.
Immutable Data types in Python
1. Numeric
2. String
3. Tuple
Mutable Data types in Python
1. List
2. Dictionary
3. Set

1. Numeric Data Type in Python

Integer – In Python 3, there is no upper bound on the integer number which means we can have the value as large as our system memory allows.

# Integer number
num = 100
print(num)
print("Data Type of variable num is", type(num))

Long – Long data type is deprecated in Python 3 because there is no need for it, since the integer has no upper limit, there is no point in having a data type that allows larger upper limit than integers.
Float – Values with decimal points are the float values, there is no need to specify the data type in Python. It is automatically inferred based on the value we are assigning to a variable. For example here fnum is a float data type.
# float number fnum = 34.45 print(fnum) print("Data Type of variable fnum is", type(fnum))

Complex Number – Numbers with real and imaginary parts are known as complex numbers. Unlike other programming language such as Java, Python is able to identify these complex numbers with the values. In the following example when we print the type of the variable cnum, it prints as complex number.

# complex number
cnum = 3 + 4j
print(cnum)
print("Data Type of variable cnum is", type(cnum))

Binary, Octal and Hexadecimal numbers

In Python we can print decimal equivalent of binary, octal and hexadecimal numbers using the prefixes.
0b(zero + ‘b’) and 0B(zero + ‘B’) – Binary Number
0o(zero + ‘o’) and 0O(zero + ‘O’) – Octal Number
0x(zero + ‘x’) and 0X(zero + ‘X’) – Hexadecimal Number
# integer equivalent of binary number 101

num = 0b101

print(num)

# integer equivalent of Octal number 32

num2 = 0o32

print(num2)

# integer equivalent of Hexadecimal number FF

num3 = 0xFF

print(num3)

2. Python Data Type – String

String is a sequence of characters in Python. The data type of String in Python is called “str”.
Strings in Python are either enclosed with single quotes or double quotes. In the following example we have demonstrated two strings one with the double quotes and other string s2 with the single quotes.

# Python program to print strings and type

s = "This is a String"
s2 = 'This is also a String'

# displaying string s and its type
print(s)
print(type(s))

# displaying string s2 and its type
print(s2)
print(type(s2))

3. Python Data Type – Tuple

Tuple is immutable data type in Python which means it cannot be changed. It is an ordered collection of elements enclosed in round brackets and separated by commas.
# tuple of integers

t1 = (1, 2, 3, 4, 5)

# prints entire tuple

print(t1)

# tuple of strings

t2 = ("hi", "hello", "bye")

# loop through tuple elements

for s in t2:

print (s)

# tuple of mixed type elements

t3 = (2, "Lucy", 45, "Steve")

'''

Print a specific element

indexes start with zero

'''

print(t3[2])

4. Python Data Type – List

List is similar to tuple, it is also an ordered collection of elements, however list is a mutable data type which means it can be changed unlike tuple which is an immutable data type.
A list is enclosed with square brackets and elements are separated by commas.

# list of integers
lis1 = (1, 2, 3, 4, 5)
# prints entire list
print(lis1)

# list of strings
lis2 = ("Apple", "Orange", "Banana")
# loop through tuple elements
for x in lis2:
    print (x)

# List of mixed type elements
lis3 = (20, "Chaitanya", 15, "BeginnersBook")
'''
Print a specific element in list
indexes start with zero
'''
print("Element at index 3 is:",lis3[3])

5. Python Data Type – Dictionary

Dictionary is a collection of key and value pairs. A dictionary doesn’t allow duplicate keys but the values can be duplicate. It is an ordered, indexed and mutable collection of elements.

The keys in a dictionary doesn’t necessarily to be a single data type, as you can see in the following example that we have 1 integer key and two string keys.

# Dictionary example

dict = {1:"Chaitanya","lastname":"Singh", "age":31}

# prints the value where key value is 1
print(dict[1])
# prints the value where key value is "lastname"
print(dict["lastname"])
# prints the value where key value is "age"
print(dict["age"])

6. Python Data Type – Set

A set is an unordered and unindexed collection of items. This means when we print the elements of a set they will appear in the random order and we cannot access the elements of set based on indexes because it is unindexed.
Elements of set are separated by commas and enclosed in curly braces. Lets take an example to understand the sets in Python.

# Set Example
myset = {"hi", 2, "bye", "Hello World"}

# loop through set
for a in myset:
    print(a)

# checking whether 2 exists in myset
print(2 in myset)

# adding new element
myset.add(99)
print(myset)

Python If Statement explained with examples

if statements are control flow statements which helps us to run a particular code only when a certain condition is satisfied. For example, you want to print a message on the screen only when a condition is true then you can use if statement to accomplish this in programming. In this guide, we will learn how to use if statements in Python programming with the help of examples.

There are other control flow statements available in Python such as if..else, if..elif..else,
nested if etc. However in this guide, we will only cover the if statements, other control statements are covered in separate tutorials.

Syntax of If statement in Python

The syntax of if statement in Python is pretty simple.

if condition:
   block_of_code

If statement flow diagram

Python – If statement Example

flag = True
if flag==True:
    print("Welcome")
    print("To")
    print("BeginnersBook.com")

Output:

Welcome
To
BeginnersBook.com

In the above example we are checking the value of flag variable and if the value is True then we are executing few print statements. The important point to note here is that even if we do not compare the value of flag with the ‘True’ and simply put ‘flag’ in place of condition, the code would run just fine so the better way to write the above code would be:

flag = True
if flag:
    print("Welcome")
    print("To")
    print("BeginnersBook.com")

By seeing this we can understand how if statement works. The output of the condition would either be true or false. If the outcome of condition is true then the statements inside body of ‘if’ executes, however if the outcome of condition is false then the statements inside ‘if’ are skipped. Lets take another example to understand this:

flag = False
if flag:
    print("You Guys")
    print("are")
    print("Awesome")

The output of this code is none, it does not print anything because the outcome of condition is ‘false’.

Python if example without boolean variables

In the above examples, we have used the boolean variables in place of conditions. However we can use any variables in our conditions. For example:

num = 100
if num < 200:
    print("num is less than 200")

Output:

num is less than 200

Python If else Statement Example

We use if statements when we need to execute a certain block of Python code when a particular condition is true. If..else statements are like extension of ‘if’ statements, with the help of if..else we can execute certain statements if condition is true and a different set of statements if condition is false. For example, you want to print ‘even number’ if the number is even and ‘odd number’ if the number is not even, we can accomplish this with the help of if..else statement.

Python – Syntax of if..else statement

if condition:
   block_of_code_1
else:
   block_of_code_2

block_of_code_1: This would execute if the given condition is true
block_of_code_2: This would execute if the given condition is false

If..else flow control

If-else example in Python

num = 22
if num % 2 == 0:
    print("Even Number")
else:
    print("Odd Number")

Python If elif else statement example

we will learn if elif else statement in Python. The if..elif..else statement is used when we need to check multiple conditions.

Syntax of if elif else statement in Python

This way we are checking multiple conditions.

if condition:
   block_of_code_1
elif condition_2:
   block_of_code_2
elif condition_3:
   block_of_code_3
..
..
..
else:
  block_of_code_n

Notes:
1. There can be multiple ‘elif’ blocks, however there is only ‘else’ block is allowed.
2. Out of all these blocks only one block_of_code gets executed. If the condition is true then the code inside ‘if’ gets executed, if condition is false then the next condition(associated with elif) is evaluated and so on. If none of the conditions is true then the code inside ‘else’ gets executed.

Python – if..elif..else statement example

In this example, we are checking multiple conditions using if..elif..else statement.

num = 1122
if 9 < num < 99:
    print("Two digit number")
elif 99 < num < 999:
    print("Three digit number")
elif 999 < num < 9999:
    print("Four digit number")
else:
    print("number is <= 9 or >= 9999")

Python Nested If else statement

we will learn the nesting of these control statements.

When there is an if statement (or if..else or if..elif..else) is present inside another if statement (or if..else or if..elif..else) then this is calling the nesting of control statements.

Nested if..else statement example

Here we have a if statement inside another if..else statement block. Nesting control statements makes us to check multiple conditions.

num = -99
if num > 0:
    print("Positive Number")
else:
    print("Negative Number")
    #nested if
    if -99<=num:
        print("Two digit Negative Number")

Output:

Negative Number
Two digit Negative Number

Python for Loop explained with examples

A loop is a used for iterating over a set of statements repeatedly. In Python we have three types of loops for, while and do-while. In this guide, we will learn for loop and the other two loops are covered in the separate tutorials.

Syntax of For loop in Python

for <variable> in <sequence>:  
   # body_of_loop that has set of statements
   # which requires repeated execution

Here <variable> is a variable that is used for iterating over a <sequence>. On every iteration it takes the next value from <sequence> until the end of sequence is reached.
Lets take few examples of for loop to understand the usage.

Python – For loop example

The following example shows the use of for loop to iterate over a list of numbers. In the body of for loop we are calculating the square of each number present in list and displaying the same.

# Program to print squares of all numbers present in a list

# List of integer numbers
numbers = [1, 2, 4, 6, 11, 20]

# variable to store the square of each num temporary
sq = 0

# iterating over the given list
for val in numbers:
    # calculating square of each number
    sq = val * val
    # displaying the squares
    print(sq)

Output:

Function range()

In the above example, we have iterated over a list using for loop. However we can also use a range() function in for loop to iterate over numbers defined by range().
range(n): generates a set of whole numbers starting from 0 to (n-1).
For example:
range(8) is equivalent to [0, 1, 2, 3, 4, 5, 6, 7]
range(start, stop): generates a set of whole numbers starting from start to stop-1.
For example:
range(5, 9) is equivalent to [5, 6, 7, 8]
range(start, stop, step_size): The default step_size is 1 which is why when we didn’t specify the step_size, the numbers generated are having difference of 1. However by specifying step_size we can generate numbers having the difference of step_size.
For example:
range(1, 10, 2) is equivalent to [1, 3, 5, 7, 9]
Lets use the range() function in for loop:

Python for loop example using range() function

Here we are using range() function to calculate and display the sum of first 5 natural numbers.

# Program to print the sum of first 5 natural numbers

# variable to store the sum
sum = 0

# iterating over natural numbers using range()
for val in range(1, 6):
    # calculating sum
    sum = sum + val

# displaying sum of first 5 natural numbers
print(sum)

Output:

For loop with else block

Unlike Java, In Python we can have an optional ‘else’ block associated with the loop. The ‘else’ block executes only when the loop has completed all the iterations. Lets take an example:

for val in range(5):
 print(val)
else:
 print("The loop has completed execution")

Output:

0
1
2
3
4
The loop has completed execution

Note: The else block only executes when the loop is finished.

Nested For loop in Python

When a for loop is present inside another for loop then it is called a nested for loop. Lets take an example of nested for loop.

for num1 in range(3):
 for num2 in range(10, 14):
  print(num1, ",", num2)

Output:

Python While Loop

While loop is used to iterate over a block of code repeatedly until a given condition returns false. In the last tutorial, we have seen for loop in Python, which is also used for the same purpose. The main difference is that we use while loop when we are not certain of the number of times the loop requires execution, on the other hand when we exactly know how many times we need to run the loop, we use for loop.

Syntax of while loop

while condition:
    #body_of_while

The body_of_while is set of Python statements which requires repeated execution. These set of statements execute repeatedly until the given condition returns false.

Flow of while loop

1. First the given condition is checked, if the condition returns false, the loop is terminated and the control jumps to the next statement in the program after the loop.
2. If the condition returns true, the set of statements inside loop are executed and then the control jumps to the beginning of the loop for next iteration.
These two steps happen repeatedly as long as the condition specified in while loop remains true.

Python – While loop example

Here is an example of while loop. In this example, we have a variable num and we are displaying the value of num in a loop, the loop has a increment operation where we are increasing the value of num. This is very important step, the while loop must have a increment or decrement operation, else the loop will run indefinitely, we will cover this later in infinite while loop.

num = 1
# loop will repeat itself as long as
# num < 10 remains true
while num < 10:
    print(num)
    #incrementing the value of num
    num = num + 3

Output:

1
4
7

Infinite while loop

Example 1:
This will print the word ‘hello’ indefinitely because the condition will always be true.

while True:
   print("hello")

Example 2:

num = 1
while num<5:
   print(num)

This will print ‘1’ indefinitely because inside loop we are not updating the value of num, so the value of num will always remain 1 and the condition num < 5 will always return true.

Nested while loop in Python

When a while loop is present inside another while loop then it is called nested while loop. Lets take an example to understand this concept.

i = 1
j = 5
while i < 4:
    while j < 8:
        print(i, ",", j)
        j = j + 1
        i = i + 1

Output:

1 , 5
2 , 6
3 , 7

Python – while loop with else block

We can have a ‘else’ block associated with while loop. The ‘else’ block is optional. It executes only after the loop finished execution.

num = 10
while num > 6:
   print(num)
   num = num-1
else:
   print("loop is finished")

Output:

10
9
8
7
loop is finished

Python break Statement

The break statement is used to terminate the loop when a certain condition is met. We already learned in previous tutorials (for loop and while loop) that a loop is used to iterate a set of statements repeatedly as long as the loop condition returns true. The break statement is generally used inside a loop along with a if statement so that when a particular condition (defined in if statement) returns true, the break statement is encountered and the loop terminates.
For example, lets say we are searching an element in a list, so for that we are running a loop starting from the first element of the list to the last element of the list. Using break statement, we can terminate the loop as soon as the element is found because why run the loop unnecessary till the end of list when our element is found. We can achieve this with the help of break statement (we will see this example programmatically in the example section below).

Syntax of break statement in Python

The syntax of break statement in Python is similar to what we have seen in Java.

break

Flow diagram of break

Example of break statement

In this example, we are searching a number ’88’ in the given list of numbers. The requirement is to display all the numbers till the number ’88’ is found and when it is found, terminate the loop and do not display the rest of the numbers.

# program to display all the elements before number 88
for num in [11, 9, 88, 10, 90, 3, 19]:
   print(num)
   if(num==88):
    print("The number 88 is found")
    print("Terminating the loop")
    break

Output:

11
9
88
The number 88 is found
Terminating the loop

Note: You would always want to use the break statement with a if statement so that only when the condition associated with ‘if’ is true then only break is encountered. If you do not use it with ‘if’ statement then the break statement would be encountered in the first iteration of loop and the loop would always terminate on the first iteration.

Python Continue Statement

The continue statement is used inside a loop to skip the rest of the statements in the body of loop for the current iteration and jump to the beginning of the loop for next iteration. The break and continue statements are used to alter the flow of loop, break terminates the loop when a condition is met and continue skip the current iteration.

Syntax of continue statement in Python

The syntax of continue statement in Python is similar to what we have seen in Java(except the semicolon)

continue

Flow diagram of continue

Example of continue statement

Lets say we have a list of numbers and we want to print only the odd numbers out of that list. We can do this by using continue statement.
We are skipping the print statement inside loop by using continue statement when the number is even, this way all the even numbers are skipped and the print statement executed for all the odd numbers.

# program to display only odd numbers
for num in [20, 11, 9, 66, 4, 89, 44]:
    # Skipping the iteration when number is even
    if num%2 == 0:
        continue
    # This statement will be skipped for all even numbers
    print(num)

Output:

11
9
89

Python pass Statement

The pass statement acts as a placeholder and usually used when there is no need of code but a statement is still required to make a code syntactically correct. For example we want to declare a function in our code but we want to implement that function in future, which means we are not yet ready to write the body of the function. In this case we cannot leave the body of function empty as this would raise error because it is syntactically incorrect, in such cases we can use pass statement which does nothing but makes the code syntactically correct.

Pass statement vs comment

You may be wondering that a python comment works similar to the pass statement as it does nothing so we can use comment in place of pass statement. Well, it is not the case, a comment is not a placeholder and it is completely ignored by the Python interpreter while on the other hand pass is not ignored by interpreter, it says the interpreter to do nothing.

Python pass statement example

If the number is even we are doing nothing and if it is odd then we are displaying the number.

for num in [20, 11, 9, 66, 4, 89, 44]:
    if num%2 == 0:
        pass
    else:
        print(num)

Output:

11
9
89

Other examples:

A function that does nothing(yet), may be implemented in future.

def f(arg): pass    # a function that does nothing (yet)

A class that does not have any methods(yet), may have methods in future implementation.

class C: pass       # a class with no methods (yet)

Python Functions

we will learn about functions in Python. A function is a block of code that contains one or more Python statements and used for performing a specific task.

Why use function in Python?

As I mentioned above, a function is a block of code that performs a specific task. Lets discuss what we can achieve in Python by using functions in our code:
1. Code re-usability: Lets say we are writing an application in Python where we need to perform a specific task in several places of our code, assume that we need to write 10 lines of code to do that specific task. It would be better to write those 10 lines of code in a function and just call the function wherever needed, because writing those 10 lines every time you perform that task is tedious, it would make your code lengthy, less-readable and increase the chances of human errors.
2. Improves Readability: By using functions for frequent tasks you make your code structured and readable. It would be easier for anyone to look at the code and be able to understand the flow and purpose of the code.
3. Avoid redundancy: When you no longer repeat the same lines of code throughout the code and use functions in places of those, you actually avoiding the redundancy that you may have created by not using functions.

Syntax of functions in Python

Function declaration:
def function_name(function_parameters): function_body # Set of Python statements return # optional return statement Calling the function:
# when function doesn't return anything function_name(parameters) OR
# when function returns something # variable is to store the returned value variable = function_name(parameters)

Python Function example

Here we have a function add() that adds two numbers passed to it as parameters. Later after function declaration we are calling the function twice in our program to perform the addition.
def add(num1, num2): return num1 + num2 sum1 = add(100, 200) sum2 = add(8, 9) print(sum1) print(sum2) Output:
300 17

Default arguments in Function

Now that we know how to declare and call a function, lets see how can we use the default arguments. By using default arguments we can avoid the errors that may arise while calling a function without passing all the parameters. Lets take an example to understand this:
In this example we have provided the default argument for the second parameter, this default argument would be used when we do not provide the second parameter while calling this function.
# default argument for second parameter def add(num1, num2=1): return num1 + num2 sum1 = add(100, 200) sum2 = add(8) # used default argument for second param sum3 = add(100) # used default argument for second param print(sum1) print(sum2) print(sum3) Output:
300 9 101

Types of functions

There are two types of functions in Python:
1. Built-in functions: These functions are predefined in Python and we need not to declare these functions before calling them. We can freely invoke them as and when needed.
2. User defined functions: The functions which we create in our code are user-defined functions. The add() function that we have created in above examples is a user-defined function.

Python Recursion

A function is said to be a recursive if it calls itself. For example, lets say we have a function abc() and in the body of abc() there is a call to the abc().

Python example of Recursion

In this example we are defining a user-defined function factorial(). This function finds the factorial of a number by calling itself repeatedly until the base case(We will discuss more about base case later, after this example) is reached.

# Example of recursion in Python to
# find the factorial of a given number

def factorial(num):
    """This function calls itself to find
    the factorial of a number"""

    if num == 1:
        return 1
    else:
        return (num * factorial(num - 1))


num = 5
print("Factorial of", num, "is: ", factorial(num))

Output:

Factorial of 5 is:  120

Lets see what happens in the above example:

factorial(5) returns 5 * factorial(5-1) 
    i.e. 5 * factorial(4)
               |__5*4*factorial(3)
                      |__5*4*3*factorial(2)
                           |__5*4*3*2*factorial(1)

Note: factorial(1) is a base case for which we already know the value of factorial. The base case is defined in the body of function with this code:

if num == 1:
    return 1

What is a base case in recursion

When working with recursion, we should define a base case for which we already know the answer. In the above example we are finding factorial of an integer number and we already know that the factorial of 1 is 1 so this is our base case.
Each successive recursive call to the function should bring it closer to the base case, which is exactly what we are doing in above example.
We use base case in recursive function so that the function stops calling itself when the base case is reached. Without the base case, the function would keep calling itself indefinitely.

Why use recursion in programming?

We use recursion to break a big problem in small problems and those small problems into further smaller problems and so on. At the end the solutions of all the smaller subproblems are collectively helps in finding the solution of the big main problem.

Advantages of recursion

Recursion makes our program:
1. Easier to write.
2. Readable – Code is easier to read and understand.
3. Reduce the lines of code – It takes less lines of code to solve a problem using recursion.

Disadvantages of recursion

1. Not all problems can be solved using recursion.
2. If you don’t define the base case then the code would run indefinitely.
3. Debugging is difficult in recursive functions as the function is calling itself in a loop and it is hard to understand which call is causing the issue.
4. Memory overhead – Call to the recursive function is not memory efficient.

Python Numbers

we will see how to work with numbers in Python. Python supports integers, floats and complex numbers.

An integer is a number without decimal point for example 5, 6, 10 etc.
A float is a number with decimal point for example 6.7, 6.0, 10.99 etc.
A complex number has a real and imaginary part for example 7+8j, 8+11j etc.

Example: Numbers in Python

# Python program to display numbers of
# different data types

# int
num1 = 10
num2 = 100
print(num1+num2)

# float
a = 10.5
b = 8.9
print(a-b)

# complex numbers
x = 3 + 4j
y = 9 + 8j
print(y-x)

Output:

110
1.5999999999999996
(6+4j)

Python example to find the class(data type) of a number

We can use the type() function to find out the class of a number. An integer number belongs to int class, a float number belongs to float class and a complex number belongs to complex class.

# program to find the class of a number

# int
num = 100
print("type of num: ",type(num))

# float
num2 = 10.99
print("type of num2: ",type(num2))

# complex numbers
num3 = 3 + 4j
print("type of num3: ",type(num3))

Output:

The isinstance() function

The isinstance() functions checks whether a number belongs to a particular class and returns true or false based on the result.
For example:
isinstance(num, int) will return true if the number num is an integer number.
isinstance(num, int) will return false if the number num is not an integer number.

Example of isinstance() function

num = 100
# true because num is an integer
print(isinstance(num, int))

# false because num is not a float
print(isinstance(num, float))

# false because num is not a complex number
print(isinstance(num, complex))

Output:

True
False
False

Python List with examples

we will discuss lists in Python. A list is a data type that allows you to store various types data in it. List is a compound data type which means you can have different-2 data types under a list, for example we can have integer, float and string items in a same list.

Create a List in Python

Lets see how to create a list in Python. To create a list all you have to do is to place the items inside a square bracket [] separated by comma ,.

# list of floats
num_list = [11.22, 9.9, 78.34, 12.0]

# list of int, float and strings
mix_list = [1.13, 2, 5, "beginnersbook", 100, "hi"]

# an empty list
nodata_list = []

As we have seen above, a list can have data items of same type or different types. This is the reason list comes under compound data type.

Accessing the items of a list

Syntax to access the list items:

list_name[index]

Example:

# a list of numbers
numbers = [11, 22, 33, 100, 200, 300]

# prints 11
print(numbers[0])

# prints 300
print(numbers[5])

# prints 22
print(numbers[1])

Output:

11
300
22

Points to Note:
1. The index cannot be a float number.
For example:

# a list of numbers
numbers = [11, 22, 33, 100, 200, 300]

# error
print(numbers[1.0])

Output:

TypeError: list indices must be integers or slices, not float

2. The index must be in range to avoid IndexError. The range of the index of a list having 10 elements is 0 to 9, if we go beyond 9 then we will get IndexError. However if we go below 0 then it would not cause issue in certain cases, we will discuss that in our next section.
For example:

# a list of numbers
numbers = [11, 22, 33, 100, 200, 300]

# error
print(numbers[6])

Output:

IndexError: list index out of range

Negative Index to access the list items from the end

Unlike other programming languages where negative index may cause issue, Python allows you to use negative indexes. The idea behind this to allow you to access the list elements starting from the end. For example an index of -1 would access the last element of the list, -2 second last, -3 third last and so on.

1 Example of Negative indexes in Python

# a list of strings
my_list = ["hello", "world", "hi", "bye"]

# prints "bye"
print(my_list[-1])

# prints "world"
print(my_list[-3])

# prints "hello"
print(my_list[-4])

Output:

bye
world
hello

How to get a sublist in Python using slicing

We can get a sublist from a list in Python using slicing operation. Lets say we have a list n_list having 10 elements, then we can slice this list using colon : operator. Lets take an example to understand this:

1 Slicing example

# list of numbers
n_list = [1, 2, 3, 4, 5, 6, 7]

# list items from 2nd to 3rd
print(n_list[1:3])

# list items from beginning to 3rd
print(n_list[:3])

# list items from 4th to end of list
print(n_list[3:])

# Whole list
print(n_list[:])

Output:

[2, 3]
[1, 2, 3]
[4, 5, 6, 7]
[1, 2, 3, 4, 5, 6, 7]

List Operations

There are various operations that we can perform on Lists.

1 Addition

There are several ways you can add elements to a list.

# list of numbers
n_list = [1, 2, 3, 4]

# 1. adding item at the desired location
# adding element 100 at the fourth location
n_list.insert(3, 100)

# list: [1, 2, 3, 100, 4]
print(n_list)

# 2. adding element at the end of the list
n_list.append(99)

# list: [1, 2, 3, 100, 4, 99]
print(n_list)

# 3. adding several elements at the end of list
# the following statement can also be written like this:
# n_list + [11, 22]
n_list.extend([11, 22])

# list: [1, 2, 3, 100, 4, 99, 11, 22]
print(n_list)

Output:

[1, 2, 3, 100, 4]
[1, 2, 3, 100, 4, 99]
[1, 2, 3, 100, 4, 99, 11, 22]

2 Update elements

We can change the values of elements in a List. Lets take an example to understand this:

# list of numbers
n_list = [1, 2, 3, 4]

# Changing the value of 3rd item
n_list[2] = 100

# list: [1, 2, 100, 4]
print(n_list)

# Changing the values of 2nd to fourth items
n_list[1:4] = [11, 22, 33]

# list: [1, 11, 22, 33]
print(n_list)

Output:

[1, 2, 100, 4]
[1, 11, 22, 33]

3 Delete elements

# list of numbers
n_list = [1, 2, 3, 4, 5, 6]

# Deleting 2nd element
del n_list[1]

# list: [1, 3, 4, 5, 6]
print(n_list)

# Deleting elements from 3rd to 4th
del n_list[2:4]

# list: [1, 3, 6]
print(n_list)

# Deleting the whole list
del n_list

Output:

[1, 3, 4, 5, 6]
[1, 3, 6]

4 Deleting elements using remove(), pop() and clear() methods

remove(item): Removes specified item from list.
pop(index): Removes the element from the given index.
pop(): Removes the last element.
clear(): Removes all the elements from the list.

# list of chars
ch_list = ['A', 'F', 'B', 'Z', 'O', 'L']

# Deleting the element with value 'B'
ch_list.remove('B')

# list: ['A', 'F', 'Z', 'O', 'L']
print(ch_list)

# Deleting 2nd element
ch_list.pop(1)

# list: ['A', 'Z', 'O', 'L']
print(ch_list)

# Deleting all the elements
ch_list.clear()

# list: []
print(ch_list)

Output:

['A', 'F', 'Z', 'O', 'L']
['A', 'Z', 'O', 'L']
[]

Python Strings

A string is usually a bit of text (sequence of characters). In Python we use ” (double quotes) or ‘ (single quotes) to represent a string. In this guide we will see how to create, access, use and manipulate strings in Python programming language.

How to create a String in Python

There are several ways to create strings in Python.
1. We can use ‘ (single quotes), see the string str in the following code.
2. We can use ” (double quotes), see the string str2 in the source code below.
3. Triple double quotes “”” and triple single quotes ”’ are used for creating multi-line strings in Python. See the strings str3 and str4 in the following example.

# lets see the ways to create strings in Python
str = 'beginnersbook'
print(str)

str2 = "Chaitanya"
print(str2)

# multi-line string
str3 = """Welcome to 
   Beginnersbook.com"""
print(str3)

str4 = '''This is a tech 
   blog'''
print(str4)

Output:

beginnersbook
Chaitanya
Welcome to 
   Beginnersbook.com
This is a tech 
   blog

How to access strings in Python

A string is nothing but an array of characters so we can use the indexes to access the characters of a it. Just like arrays, the indexes start from 0 to the length-1.

You will get IndexError if you try to access the character which is not in the range. For example,
if a string is of length 6 and you try to access the 8th char of it then you will get this error.
You will get TypeError if you do not use integers as indexes, for example if you use a float as an index then you will get this error.

str = "Kevin"

# displaying whole string
print(str)

# displaying first character of string
print(str[0])

# displaying third character of string
print(str[2])

# displaying the last character of the string
print(str[-1])

# displaying the second last char of string
print(str[-2])

Output:

Kevin
K
v
n
i

Python String Operations

Lets see the operations that can be performed on the strings.

1. Getting a substring in Python – Slicing operation

We can slice a string to get a substring out of it. To understand the concept of slicing we must understand the positive and negative indexes in Python (see the example above to understand this). Lets take a look at the few examples of slicing.

str = "Beginnersbook"

# displaying whole string
print("The original string is: ", str)

# slicing 10th to the last character
print("str[9:]: ", str[9:])

# slicing 3rd to 6th character
print("str[2:6]: ", str[2:6])

# slicing from start to the 9th character
print("str[:9]: ", str[:9])

# slicing from 10th to second last character
print("str[9:-1]: ", str[9:-1])

Output:

The original string is:  Beginnersbook
str[9:]:  book
str[2:6]:  ginn
str[:9]:  Beginners
str[9:-1]:  boo

2 Concatenation of strings in Python

The + operator is used for string concatenation in Python. Lets take an example to understand this:

str1 = "One"
str2 = "Two"
str3 = "Three"

# Concatenation of three strings
print(str1 + str2 + str3)

Output:

OneTwoThree

Note: When + operator is used on numbers it adds them but when it used on strings it concatenates them. However if you try to use this between string and number then it will throw TypeError.
For example:

s = "one"
n = 2
print(s+n)

Output:

TypeError: must be str, not int

3 Repetition of string – Replication operator

We can use * operator to repeat a string by specified number of times.

str = "ABC"

# repeating the string str by 3 times
print(str*3)

Output:

ABCABCABC

4 Python Membership Operators in Strings

in: This checks whether a string is present in another string or not. It returns true if the entire string is found else it returns false.
not in: It works just opposite to what “in” operator does. It returns true if the string is not found in the specified string else it returns false.

str = "Welcome to beginnersbook.com"
str2 = "Welcome"
str3 = "Chaitanya"
str4 = "XYZ"

# str2 is in str? True
print(str2 in str)

# str3 is in str? False
print(str3 in str)

# str4 not in str? True
print(str4 not in str)

Output:

True
False
True

5 Python – Relational Operators on Strings

The relational operators works on strings based on the ASCII values of characters.
The ASCII value of a is 97, b is 98 and so on.
The ASCII value of A is 65, B is 66 and so on.

str = "ABC"
str2 = "aBC"
str3 = "XYZ"
str4 = "XYz"

# ASCII value of str2 is > str? True
print(str2 > str)

# ASCII value of str3 is > str4? False
print(str3 > str4)

Output:

True
False

Python Tuple with example

a tuple is similar to List except that the objects in tuple are immutable which means we cannot 
change the elements of a tuple once assigned. On the other hand, we can 
change the elements of a list.

Tuple vs List

1. The elements of a list are mutable whereas the elements of a tuple are immutable.
2. When we do not want to change the data over time, the tuple is a preferred data type whereas when we need to change the data in future, list would be a wise option.
3. Iterating over the elements of a tuple is faster compared to iterating over a list.
4. Elements of a tuple are enclosed in parenthesis whereas the elements of list are enclosed in square bracket.

How to create a tuple in Python

To create a tuple in Python, place all the elements in a () parenthesis, separated by commas. A tuple can have heterogeneous data items, a tuple can have string and list as data items as well.

1 Example – Creating tuple

In this example, we are creating few tuples. We can have tuple of same type of data items as well as mixed type of data items. This example also shows nested tuple (tuples as data items in another tuple).

# tuple of strings
my_data = ("hi", "hello", "bye")
print(my_data)

# tuple of int, float, string
my_data2 = (1, 2.8, "Hello World")
print(my_data2)

# tuple of string and list
my_data3 = ("Book", [1, 2, 3])
print(my_data3)

# tuples inside another tuple
# nested tuple
my_data4 = ((2, 3, 4), (1, 2, "hi"))
print(my_data4)

Output:

('hi', 'hello', 'bye')
(1, 2.8, 'Hello World')
('Book', [1, 2, 3])
((2, 3, 4), (1, 2, 'hi'))

2 Empty tuple:

# empty tuple
my_data = ()

3 Tuple with only single element:

Note: When a tuple has only one element, we must put a comma after the element, otherwise Python will not treat it as a tuple.

# a tuple with single data item
my_data = (99,)

If we do not put comma after 99 in the above example then python will treat my_data as an int variable rather than a tuple.

How to access tuple elements

We use indexes to access the elements of a tuple. Lets take few example to understand the working.

1 Accessing tuple elements using positive indexes

We can also have negative indexes in tuple, we have discussed that in the next section. Indexes starts with 0 that is why we use 0 to access the first element of tuple, 1 to access second element and so on.

# tuple of strings
my_data = ("hi", "hello", "bye")

# displaying all elements
print(my_data)

# accessing first element
# prints "hi"
print(my_data[0])

# accessing third element
# prints "bye"
print(my_data[2])

Output:

('hi', 'hello', 'bye')
hi
bye

Note:
1. TypeError: If you do not use integer indexes in the tuple. For example my_data[2.0] will raise this error. The index must always be an integer.
2. IndexError: Index out of range. This error occurs when we mention the index which is not in the range. For example, if a tuple has 5 elements and we try to access the 7th element then this error would occurr.

2 Negative indexes in tuples

Similar to list and strings we can use negative indexes to access the tuple elements from the end.
-1 to access last element, -2 to access second last and so on.

my_data = (1, 2, "Kevin", 8.9)

# accessing last element
# prints 8.9
print(my_data[-1])

# prints 2
print(my_data[-3])

Output:

8.9
2

3 Accessing elements from nested tuples

Lets understand how the double indexes are used to access the elements of nested tuple. The first index represents the element of main tuple and the second index represent the element of the nested tuple.
In the following example, when I used my_data[2][1], it accessed the second element of the nested tuple. Because 2 represented the third element of main tuple which is a tuple and the 1 represented the second element of that tuple.

my_data = (1, "Steve", (11, 22, 33))

# prints 'v'
print(my_data[1][3])

# prints 22
print(my_data[2][1])

Output:

v
22

Operations that can be performed on tuple in Python

Lets see the operations that can be performed on the tuples in Python.

1 Changing the elements of a tuple

We cannot change the elements of a tuple because elements of tuple are immutable. However we can change the elements of nested items that are mutable. For example, in the following code, we are changing the element of the list which is present inside the tuple. List items are mutable that’s why it is allowed.

my_data = (1, [9, 8, 7], "World")
print(my_data)

# changing the element of the list
# this is valid because list is mutable
my_data[1][2] = 99
print(my_data)

# changing the element of tuple
# This is not valid since tuple elements are immutable
# TypeError: 'tuple' object does not support item assignment
# my_data[0] = 101
# print(my_data)

Output:

(1, [9, 8, 7], 'World')
(1, [9, 8, 99], 'World')

2 Delete operation on tuple

We already discussed above that tuple elements are immutable which also means that we cannot delete the elements of a tuple. However deleting entire tuple is possible.

my_data = (1, 2, 3, 4, 5, 6)
print(my_data)

# not possible
# error
# del my_data[2]

# deleting entire tuple is possible
del my_data

# not possible
# error
# because my_data is deleted
# print(my_data)

Output:

(1, 2, 3, 4, 5, 6)

3 Slicing operation in tuples

my_data = (11, 22, 33, 44, 55, 66, 77, 88, 99)
print(my_data)

# elements from 3rd to 5th
# prints (33, 44, 55)
print(my_data[2:5])

# elements from start to 4th
# prints (11, 22, 33, 44)
print(my_data[:4])

# elements from 5th to end
# prints (55, 66, 77, 88, 99)
print(my_data[4:])

# elements from 5th to second last
# prints (55, 66, 77, 88)
print(my_data[4:-1])

# displaying entire tuple
print(my_data[:])

Output:

(11, 22, 33, 44, 55, 66, 77, 88, 99)
(33, 44, 55)
(11, 22, 33, 44)
(55, 66, 77, 88, 99)
(55, 66, 77, 88)
(11, 22, 33, 44, 55, 66, 77, 88, 99)

4 Membership Test in Tuples

in: Checks whether an element exists in the specified tuple.
not in: Checks whether an element does not exist in the specified tuple.

my_data = (11, 22, 33, 44, 55, 66, 77, 88, 99)
print(my_data)

# true
print(22 in my_data)

# false
print(2 in my_data)

# false
print(88 not in my_data)

# true
print(101 not in my_data)

Output:

(11, 22, 33, 44, 55, 66, 77, 88, 99)
True
False
False
True

5 Iterating a tuple

# tuple of fruits
my_tuple = ("Apple", "Orange", "Grapes", "Banana")

# iterating over tuple elements
for fruit in my_tuple:
     print(fruit)

Output:

Apple
Orange
Grapes
Banana

Python Dictionary with examples

Dictionary is a mutable data type in Python. A python dictionary is a collection of key and value pairs separated by a colon (:), enclosed in curly braces {}.

Python Dictionary

Here we have a dictionary. Left side of the colon(:) is the key and right side of the : is the value.

mydict = {'StuName': 'Ajeet', 'StuAge': 30, 'StuCity': 'Agra'}

Points to Note:
1. Keys must be unique in dictionary, duplicate values are allowed.
2. A dictionary is said to be empty if it has no key value pairs. An empty dictionary is denoted like this: {}.
3. The keys of dictionary must be of immutable data types such as String, numbers or tuples.

Accessing dictionary values using keys in Python

To access a value we can can use the corresponding key in the square brackets as shown in the following example. Dictionary name followed by square brackets and in the brackets we specify the key for which we want the value.

mydict = {'StuName': 'Ajeet', 'StuAge': 30, 'StuCity': 'Agra'}
print("Student Age is:", mydict['StuAge'])
print("Student City is:", mydict['StuCity'])

Output:
If you specify a key which doesn’t exist in the dictionary then you will get a compilation error. For example. Here we are trying to access the value for key ‘StuClass’ which does not exist in the dictionary mydict, thus we get a compilation error when we run this code.

mydict = {'StuName': 'Ajeet', 'StuAge': 30, 'StuCity': 'Agra'}
print("Student Age is:", mydict['StuClass'])
print("Student City is:", mydict['StuCity'])

Output:

Change values in Dictionary

Here we are updating the values for the existing key-value pairs. To update a value in dictionary we are using the corresponding key.

mydict = {'StuName': 'Ajeet', 'StuAge': 30, 'StuCity': 'Agra'}
print("Student Age before update is:", mydict['StuAge'])
print("Student City before update is:", mydict['StuCity'])
mydict['StuAge'] = 31
mydict['StuCity'] = 'Noida'
print("Student Age after update is:", mydict['StuAge'])
print("Student City after update is:", mydict['StuCity'])

Output:

Adding a new entry (key-value pair) in dictionary

We can also add a new key-value pair in an existing dictionary. Lets take an example to understand this.

mydict = {'StuName': 'Steve', 'StuAge': 4, 'StuCity': 'Agra'}
mydict['StuClass'] = 'Jr.KG'
print("Student Name is:", mydict['StuName'])
print("Student Class is:", mydict['StuClass'])

Output:

Loop through a dictionary

We can loop through a dictionary as shown in the following example. Here we are using for loop.

mydict = {'StuName': 'Steve', 'StuAge': 4, 'StuCity': 'Agra'}
for e in mydict:
  print("Key:",e,"Value:",mydict[e])

Output:

Python delete operation on dictionary

We can delete key-value pairs as well as entire dictionary in python. Lets take an example. As you can see we can use del following by dictionary name and in square brackets we can specify the key to delete the specified key value pair from dictionary.
To delete all the entries (all key-value pairs) from dictionary we can use the clear() method.
To delete entire dictionary along with all the data use del keyword followed by dictionary name as shown in the following example.

mydict = {'StuName': 'Steve', 'StuAge': 4, 'StuCity': 'Agra'}
del mydict['StuCity']; # remove entry with key 'StuCity'
mydict.clear();     # remove all key-value pairs from mydict
del mydict ;        # delete entire dictionary mydict

Python Sets

Set is an unordered and unindexed collection of items in Python. Unordered means when we display the elements of a set, it will come out in a random order. Unindexed means, we cannot access the elements of a set using the indexes like we can do in list and tuples.

The elements of a set are defined inside square brackets and are separated by commas. For example –

myset = [1, 2, 3, 4, "hello"]

Python Set Example

# Set Example
myset = {"hi", 2, "bye", "Hello World"}
print(myset)

Output:

Checking whether an item is in the set

We can check whether an item exists in Set or not using “in” operator as shown in the following example. This returns the boolean value true or false. If the item is in the given set then it returns true, else it returns false.

# Set Example
myset = {"hi", 2, "bye", "Hello World"}

# checking whether 2 is in myset
print(2 in myset)

# checking whether "hi" is in myset
print("hi" in myset)

# checking whether "BeginnersBook" is in myset
print("BeginnersBook" in myset)

Output:

Loop through the elements of a Set in Python

We can loop through the elements of a set in Python as shown in the following elements. As you can see in the output that the elements will appear in random order each time you run the code.

# Set Example
myset = {"hi", 2, "bye", "Hello World"}

# loop through the elements of myset
for a in myset:
    print(a)

Output:

Python – Add or remove item from a Set

We can add an item in a Set using add() function and we can remove an item from a set using remove() function as shown in the following example.

# Set Example
myset = {"hi", 2, "bye", "Hello World"}
print("Original Set:", myset)

# adding an item
myset.add(99)
print("Set after adding 99:", myset)

# removing an item
myset.remove("bye")
print("Set after removing bye:", myset)

Output:

Set Methods

1. add(): This method adds an element to the Set.
2. remove(): This method removes a specified element from the Set
3. discard(): This method works same as remove() method, however it doesn’t raise an error when the specified element doesn’t exist.
4. clear(): Removes all the elements from the set.
5. copy(): Returns a shallow copy of the set.
6. difference(): This method returns a new set which is a difference between two given sets.
7. difference_update(): Updates the calling set with the Set difference of two given sets.
8. intersection(): Returns a new set which contains the elements that are common to all the sets.
9. intersection_update(): Updates the calling set with the Set intersection of two given sets.
10. isdisjoint(): Checks whether two sets are disjoint or not. Two sets are disjoint if they have no common elements.
11. issubset(): Checks whether a set is a subset of another given set.
12. pop(): Removes and returns a random element from the set.
13. union(): Returns a new set with the distinct elements of all the sets.
14. update(): Adds elements to a set from other passed iterable.
15. symmetric_difference(): Returns a new set which is a symmetric difference of two given sets.
16. symmetric_difference_update(): Updates the calling set with the symmetric difference of two given sets.

Python OOPs Concepts

Python is an object-oriented programming language. What this means is we can solve a problem in Python by creating objects in our programs. In this guide, we will discuss OOPs terms such as class, objects, methods etc. along with the Object oriented programming features such as inheritance, polymorphism, abstraction, encapsulation.

Object

An object is an entity that has attributes and behaviour. For example, Ram is an object who has attributes such as height, weight, color etc. and has certain behaviours such as walking, talking, eating etc.

Class

A class is a blueprint for the objects. For example, Ram, Shyam, Steve, Rick are all objects so we can define a template (blueprint) class Human for these objects. The class can define the common attributes and behaviours of all the objects.

Methods

As we discussed above, an object has attributes and behaviours. These behaviours are called methods in programming.

Example of Class and Objects

In this example, we have two objects Ram and Steve that belong to the class Human
Object attributes: name, height, weight
Object behaviour: eating()

How to create Class and Objects in Python

we will see how to create classes and objects in Python.

Define class in Python

A class is defined using the keyword class.

Example

In this example, we are creating an empty class DemoClass. This class has no attributes and methods.
The string that we mention in the triple quotes is a docstring which is an optional string that briefly explains the purpose of the class.

class DemoClass:
    """This is my docstring, this explains brief about the class"""

# this prints the docstring of the class
print(DemoClass.__doc__)

Output:

This is my docstring, this explains brief about the class

Creating Objects of class

In this example, we have a class MyNewClass that has an attribute num and a function hello(). We are creating an object obj of the class and accessing the attribute value of object and calling the method hello() using the object.

class MyNewClass:
    """This class demonstrates the creation of objects"""

    # instance attribute
    num = 100

    # instance method
    def hello(self):
        print("Hello World!")


# creating object of MyNewClass
obj = MyNewClass()

# prints attribute value
print(obj.num)

# calling method hello()
obj.hello()

# prints docstring
print(MyNewClass.__doc__)

Output:

100
Hello World!
This class demonstrates the creation of objects

Python Constructors – default and parameterized

A constructor is a special kind of method which is used for initializing the instance variables during object creation. In this guide, we will see what is a constructor, types of it and how to use them in the python programming with examples.

1. What is a Constructor in Python?

Constructor is used for initializing the instance members when we create the object of a class.
For example:
Here we have a instance variable num which we are initializing in the constructor. The constructor is being invoked when we create the object of the class (obj in the following example).

class DemoClass:
    # constructor
    def __init__(self):
        # initializing instance variable
        self.num=100

    # a method
    def read_number(self):
        print(self.num)


# creating object of the class. This invokes constructor
obj = DemoClass()

# calling the instance method using the object obj
obj.read_number()

Output:

1.1 Syntax of constructor declaration

As we have seen in the above example that a constructor always has a name init and the name init is prefixed and suffixed with a double underscore(__). We declare a constructor using def keyword, just like methods.

def __init__(self):
    # body of the constructor

2. Types of constructors in Python

We have two types of constructors in Python.
1. default constructor – this is the one, which we have seen in the above example. This constructor doesn’t accept any arguments.
2. parameterized constructor – constructor with parameters is known as parameterized constructor.

2.1 Python – default constructor example

Note: An object cannot be created if we don’t have a constructor in our program. This is why when we do not declare a constructor in our program, python does it for us. Lets have a look at the example below.
Example: When we do not declare a constructor
In this example, we do not have a constructor but still we are able to create an object for the class. This is because there is a default constructor implicitly injected by python during program compilation, this is an empty default constructor that looks like this:

def __init__(self):
    # no body, does nothing.

Source Code:

class DemoClass:
    num = 101

    # a method
    def read_number(self):
        print(self.num)


# creating object of the class
obj = DemoClass()

# calling the instance method using the object obj
obj.read_number()

Output:

Example: When we declare a constructor
In this case, python does not create a constructor in our program.

class DemoClass:
    num = 101

    # non-parameterized constructor
    def __init__(self):
        self.num = 999

    # a method
    def read_number(self):
        print(self.num)


# creating object of the class
obj = DemoClass()

# calling the instance method using the object obj
obj.read_number()

Output:

2.2 Python – Parameterized constructor example

When we declare a constructor in such a way that it accepts the arguments during object creation then such type of constructors are known as Parameterized constructors. As you can see that with such type of constructors we can pass the values (data) during object creation, which is used by the constructor to initialize the instance members of that object.

class DemoClass:
    num = 101

    # parameterized constructor
    def __init__(self, data):
        self.num = data

    # a method
    def read_number(self):
        print(self.num)


# creating object of the class
# this will invoke parameterized constructor
obj = DemoClass(55)

# calling the instance method using the object obj
obj.read_number()

# creating another object of the class
obj2 = DemoClass(66)

# calling the instance method using the object obj
obj2.read_number()

Output:

55
66