Introduction

Python - A Quick Start for existing Programers

2 min read

Published Sep 16 2025, updated Sep 30 2025

Python

This is a quick start guide for people that have worked in other programming languages, so know basic programming knowledge, but have never used Python and just want to pick up the syntax quickly.

General characteristics

Interpreted language - Python is not compiled into machine code beforehand. Instead, the Python interpreter reads and executes code line by line.
High-level & readable - designed to be simple, human-readable, and expressive.
Cross-platform - runs on Windows, macOS, Linux, and more.

File & execution

Python files use the extension: .py
Code runs top to bottom, line by line.
Unlike languages such as Java or C, Python does not require a main() method—execution starts directly from the first line of code.

Run the .py file by calling from the command line (assuming Python 3 is installed):

python3 myfile.p

You can also run an interactive shell that will execute code as it is entered, rather than specifying a .py file. To enter the interactive shell mode:

python3

Variables

Dynamically typed - you don’t need to declare variable types. Python infers the type at runtime.

x = 5 # int

y = "Hello" # str

z = 3.14 # float

Variable types can change:

x = 5

x = "Now a string"

Code structure

Indentation-based - Python uses indentation (whitespace) instead of {} or keywords like begin/end to define code blocks.
Indents can be tabs or spaces, but not both in the same file.
Best practice: Use 4 spaces per indent.
A : symbol is usually used to denote when an indentation will start.

Example:

# Example if statement indentation

x = 10

if x > 5:

print("x is greater than 5")

else:

print("x is not greater than 5")

# Example for loop indentation

for i in range(5):

print("Iteration", i)

# Example function definition indentation

def greet(name):