Python Syntax Cheatsheet

Quick reference for Python syntax fundamentals.

Comments

# Single-line comment

"""
Multi-line comment (docstring).
Can span multiple lines.
"""

'''
Also valid for multi-line comments.
'''

Indentation

Python uses indentation to define code blocks. Use 4 spaces per level (not tabs).

if x > 5:
    print("x is greater than 5")  # Indented 4 spaces
    if x > 10:
        print("x is greater than 10")  # Indented 8 spaces

Variables and Assignment

x = 10                    # Simple assignment
x, y = 5, 10             # Multiple assignment
x = y = 5                # Chained assignment
x, *rest = [1, 2, 3, 4]  # Unpacking (rest = [2, 3, 4])

Operators

Operator	Example	Result
+	5 + 3	8
-	5 - 3	2
*	5 * 3	15
/	5 / 2	2.5
//	5 // 2	2
%	5 % 2	1
**	5 ** 2	25
==	5 == 5	True
!=	5 != 3	True
<, >, <=, >=	5 > 3	True
and, or, not	True and False	False

Conditionals

if condition:
    # code
elif other_condition:
    # code
else:
    # code

# Ternary operator
result = value_if_true if condition else value_if_false

Loops

# For loop
for item in iterable:
    print(item)

# While loop
while condition:
    # code

# Break and continue
for i in range(10):
    if i == 3:
        continue  # Skip this iteration
    if i == 7:
        break     # Exit loop

Functions

def function_name(param1, param2=default_value):
    """Docstring describing the function."""
    return result

# Calling a function
result = function_name(arg1, arg2)

# Default arguments
def greet(name="World"):
    return f"Hello, {name}!"

# *args and **kwargs
def func(*args, **kwargs):
    print(args)    # Tuple of positional arguments
    print(kwargs)  # Dictionary of keyword arguments

Imports

import module_name
from module_name import function_name
from module_name import function_name as alias
from module_name import *  # Import all (generally avoid)
import module_name as alias

Main Guard

if __name__ == "__main__":
    # Code here runs only when script is executed directly,
    # not when imported as a module
    main()

Common Patterns

List Comprehension

squares = [x**2 for x in range(10)]
evens = [x for x in range(10) if x % 2 == 0]

Dictionary Comprehension

squares_dict = {x: x**2 for x in range(5)}

Try-Except

try:
    # code that might raise an exception
except SpecificError as e:
    # handle error
except Exception:
    # catch-all
finally:
    # always runs

With Statement

with open("file.txt") as f:
    content = f.read()
# File automatically closed

Lambda Functions

square = lambda x: x**2
result = square(5)  # 25

# Often used with map, filter, sorted
numbers = [1, 2, 3, 4, 5]
doubled = list(map(lambda x: x * 2, numbers))

String Formatting

# f-strings (preferred, Python 3.6+)
name = "Alice"
age = 30
print(f"{name} is {age} years old")

# .format()
print("{} is {} years old".format(name, age))

# % formatting (older style)
print("%s is %d years old" % (name, age))

Truthiness

Values that evaluate to False: - False, None, 0, 0.0, "", [], {}, ()

All other values evaluate to True.