Python setup and syntax

Why Python?

Python reads almost like English, has a huge standard library and is the main language for data analysis, automation and artificial intelligence. Companies use it for web backends, scripting and machine learning.

Installing Python

1. Download Python 3 (3.12 or newer) from python.org. On Windows, tick Add python.exe to PATH during installation.
2. Open a terminal and check the version:

python --version     # on macOS and Linux this may be python3 --version

1. Install a code editor such as Visual Studio Code with the Python extension.

Two ways to run Python

Interactive shell (REPL). Type python in a terminal. You'll see the >>> prompt, where each line runs immediately. It's ideal for experiments:

>>> 2 + 3
5
>>> "Dev" + "Crest"
'DevCrest'

Type exit() to leave.

Script file. Save code in a file such as hello.py:

# hello.py — my first Python program
name = input("What is your name? ")
print("Welcome to DevCrest,", name)
print("Python runs this file from top to bottom.")

Run it with python hello.py. input shows a prompt and returns what the user types as text; print displays values separated by spaces.

Syntax essentials

• No semicolons or braces. Each statement usually sits on its own line.
• Indentation defines blocks. Lines inside an if, loop or function are indented, conventionally by four spaces. Inconsistent indentation causes an IndentationError.
• Comments start with # and are ignored by Python.
• Names use snake_case, such as total_marks. They are case-sensitive: Score and score are different.

marks = 72
if marks >= 40:
    print("Passed")      # indented: part of the if block
print("Done")            # not indented: always runs

Reading errors

Python reports problems with a traceback. Read it from the bottom: the last line names the error type and message, and the lines above show where it happened.

Traceback (most recent call last):
  File "hello.py", line 3, in <module>
    print("Total:" + 5)
TypeError: can only concatenate str (not "int") to str

This one says you cannot join text and a number with +. Use print("Total:", 5) or convert with str(5).