Comments are lines that Python ignores during execution. They are used to explain code, make it more readable, or temporarily disable code.
Use the # symbol. Everything after # on that line is a comment.
# This is a single-line comment
print("Hello") # inline comment
# Comments are ignored by Python
# print("This line won't run")
Python doesn't have a dedicated multi-line comment syntax. Use multiple # lines, or use triple-quoted strings (which are technically string literals, not comments).
# Method 1: Multiple # lines
# This is line 1
# This is line 2
# This is line 3
# Method 2: Triple-quoted string (docstring style)
"""
This is a multi-line string.
Often used as a docstring at the top of
functions, classes, or modules.
"""
def greet(name):
"""
This function greets a person.
Args:
name (str): The person's name
Returns:
str: A greeting message
"""
return f"Hello, {name}!"
A variable is a named tl-container that stores a value in memory. In Python, you don't need to declare a variable's type - it's inferred automatically.
name = "Alice" # str
age = 25 # int
height = 5.7 # float
is_student = True # bool
print(name) # Alice
print(type(name)) #
print(type(age)) #
# Multiple assignment
x = y = z = 0 # all three equal 0
# Tuple unpacking
a, b, c = 1, 2, 3
print(a, b, c) # 1 2 3
# Swap variables (Python style)
a, b = b, a
print(a, b) # 2 1
# Valid variable names
my_name = "Alice"
_private = 42
camelCase = "ok but not Pythonic"
snake_case = "preferred in Python"
value2 = 100
# Invalid variable names (will cause SyntaxError)
# 2value = 10 # starts with digit
# my-name = "Bob" # hyphen not allowed
# class = "Python" # reserved keyword
# Python naming conventions (PEP 8)
user_name = "alice" # variables: snake_case
MAX_SIZE = 100 # constants: UPPER_CASE
class MyClass: # classes: PascalCase
pass
Python is dynamically typed - a variable can hold different types at different times. Use type() to check the current type.
x = 10
print(type(x)) #
x = "hello"
print(type(x)) #
x = 3.14
print(type(x)) #
x = [1, 2, 3]
print(type(x)) #
# Type hints (Python 3.5+) - optional but recommended
def add(a: int, b: int) -> int:
return a + b
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