Python Syntax

Theory

Python's syntax emphasizes readability. Unlike many languages that use curly braces or keywords, Python uses indentation to define code blocks. This forces clean, consistent formatting.

Indentation rules: All statements in a block must have the same indentation level. The standard is 4 spaces per level. Mixing tabs and spaces causes IndentationError. Indentation is required after colon-terminated headers like if, def, for, while, class, with, and try.

Comments start with # and extend to the end of the line. There are no multi-line comment syntaxes in Python, but triple-quoted strings ("""...""" or '''...''') are often used as multi-line comments or docstrings even though they're technically string literals.

Docstrings document modules, functions, classes, and methods. Enclosed in triple quotes, they appear as the first statement in a definition and are accessible via help() and __doc__.

Variables don't require explicit type declaration. Python infers the type from the assigned value. Variable names must start with a letter or underscore, followed by letters, digits, or underscores. They are case-sensitive (name and Name differ).

Naming conventions follow PEP 8:

• snake_case for variables, functions, and modules
• PascalCase for classes
• UPPER_CASE for constants
• Single leading underscore _var for internal/private use
• Double leading underscore __var for name mangling

Basic I/O:

• print() outputs to the console. It supports multiple arguments, custom separators (sep), end characters (end), and file output (file)
• input() reads a line from the user as a string. Convert with int(), float(), etc. for numeric input

Multiple assignment is a Python feature: a, b = 1, 2 assigns 1 to a and 2 to b. It also enables swapping: a, b = b, a.

Exercises

# Get user input and print a formatted sentence

Hello Alice! You are 25 years old and your favorite color is blue.

Mini Quiz