Python First Program and Python Syntax

So far, we have learned how to install Python. Here, we will learn how to write a Python program and how to run it.

Writing and Running Python Program

Write Program:
- Write the following code in Notepad or VS Code:
- print("Welcome to Python World")
Save File:
- Save the file with the name welcome.py.
Run Program:
- Type the following command in Command Prompt:
- python welcome.py

Output
Welcome to Python World

Indentation in Python

Indentation is a very important concept in Python. Indentation means spaces or tabs at the beginning of a line. In other languages, braces { } are used to group statements, but in Python, indentation is used. If indentation is incorrect, Python raises an IndentationError or TabError.

Rules of Indentation

If indentation is incorrect, the Python program will not run.
Statements inside a block (if, for, while, def) must be indented.
All lines inside the same block must have the same number of spaces.
Mixing tabs and spaces causes a TabError.
At least one space is required for each indentation level; using 4 spaces is best practice.
For nested blocks, an additional 4 spaces should be used.


# Example
x = 10
print(x)
    y = 20
    print(y)

Running this code produces IndentationError: unexpected indent.
This is because y = 20 and print(y) have extra indentation.
These statements do not belong to any block, so indentation is not required.
Indentation in Python is mandatory only to define block structure.
Statements outside blocks should not be indented.


# Example
x = 10
print(x)
if (x == 10):
    y = 20
    print(y)

This program runs successfully.
Indentation is mandatory for statements inside the if block.
Blocks such as if, for, while, and def must use indentation.
Statements outside blocks do not require indentation.

Statements in Python

A statement is an instruction given to the computer.
A program is a collection of statements.
In Python, semicolon (;) at the end of a statement is optional.
Each statement normally ends on a new line.
In languages like C, C++, and Java, semicolon is mandatory.
In Python, semicolon is not required.
To write multiple statements on the same line, semicolon can be used.
print(10); print(20)
If a statement is too long, it can be continued on the next line using backslash (\).
total = 1 + 2 + 3 + \ 4 + 5 + 6

Example for Multiline Statement in Python


x = 10
y = 20
print(x); print(y)
total = 1 + 2 + 3 + 4 + \
    5 + 6 + 7 + 8
print(total)

Output
10
20
36

In the above program:

Semicolon (;):
- Semicolon is not mandatory in Python.
- It can be used to separate multiple statements in one line.
- Example:
```
print(x); print(y)
```
- Here, two statements are written in the same line using semicolon.
Multiline (\):
- Backslash (\) allows long expressions to continue on the next line.
- Example:
```
total = 1 + 2 + 3 + 4 + \
5 + 6 + 7 + 8
                            
```
- Python treats it as a single expression.

Comments in Python

Comments are descriptive lines used to explain code. They are not executed by Python. Python supports both single-line and multi-line comments.

Single-Line Comment in Python

Single-line comments are written using the # symbol. They can be written at the beginning of the line or after a statement.


# This line prints output
print("Welcome to Python World")  # single-line comment after statement

Multi-Line Comment in Python

Multi-line comments can be written using three single quotes (''') or three double quotes (""").


'''
This is a multi-line comment
This is the second line
And so on...
'''
print("Welcome to Python World")

Example for Comments in Python


'''
This program creates two variables x and y
The addition result is assigned to sum
Finally, sum is printed
'''
x = 10
y = 20
# add x and y and assign to sum
sum = x + y
print(sum)  # printing sum value

Output
30

In this program: multi-line comments are used to describe the program, and single-line comments are written at the beginning of the line and after statements.

What We Have Learned

Writing and Running Python Program
Basic Syntax in Python
Variables in Python will be covered in the next topic

Watch the following Video for Writing and Running Python Program

← Previous Python Install Next → Python Variables and Printing Data