Introduction #

When you start with Python, you might think there is no structure because you can write statements directly at the top of the file and run them. That part is true. Python runs code from top to bottom.

But even in Python there is an effective structure people use in real projects, and understanding it early helps a lot when code grows or when you start doing bigger things than just print statements.

Python is different from C or C++. It doesn’t require a main() function by default. The interpreter starts reading your code from the first line. But we still follow a common pattern that makes code easier to read, reuse, and maintain.

Let’s look at what a typical Python file contains.

A Simple Python Program #

Here is an example:

# This is a comment
import math

def square(x):
    return x * x

print(square(5))

This looks short and simple. Now let’s understand the parts.

Comments #

Comments are lines meant for humans, not for the interpreter. They start with #.

# This is a comment explaining the code

Python ignores them while running your code. Use them to explain why something is done, not what is done — because well-written code should already tell what is happening.

Import Statements #

Imports bring code from other modules into your program.

import math

This lets you use functions defined in the math module, like math.sqrt() or math.pi. In Python, imports are usually put near the top of the file before other code. This makes it easy to see what external pieces your program needs. (Python Enhancement Proposals (PEPs))

You’ll see two common forms:

import math
from math import sqrt

Use whichever makes your code clearer.

Function Definitions #

If you want reusable logic, you put it in a function.

def square(x):
    return x * x

Functions help break your program into smaller, manageable parts. They also make testing easier. Python functions are defined using def, and the body is indented. Python uses indentation instead of {} to group statements.

Executable Code #

At the bottom of the file, you usually put the code that actually runs.

print(square(5))

This line calls the function and prints the result.

In small scripts you will write code like this directly. In larger programs, you will often wrap this in a function and then call it. That helps when you want to import the file as a module elsewhere.

Optional: if __name__ == "__main__": #

Experienced Python developers often use this construct in bigger programs:

if __name__ == "__main__":
    print(square(5))

This means: only run this part when the file is executed directly, not when it’s imported as a module. It’s not required, but it’s very common in real projects.

Indentation Is Important #

Python doesn’t use {} to mark blocks. It uses indentation. If code is not indented correctly, Python will throw an error. So always be consistent with spaces (most people use four spaces).

Why This Structure Matters #

In real projects, you will have bigger files and multiple modules. Following this structure helps other developers (and your future self) understand the code quickly:

• Imports at the top
• Function definitions next
• Execution code at the bottom

This keeps your Python programs clean and easy to manage.

Final Thoughts #

Python feels more relaxed than C or C++, but that doesn’t mean there’s no structure at all. Once you understand these parts and how they fit, you can build anything from simple scripts to larger applications.