Python Cheat Sheet

This cheat sheet provides a quick reference for the most common syntax and features in the Python programming language. For a more detailed explanation, see the main Python note.

Syntax and Variables

Python uses indentation to define code blocks. Variables are dynamically typed.

# This is a comment
name = "Alice"  # String
age = 30         # Integer
height = 5.8     # Float
is_student = True # Boolean
data = None      # NoneType

Data Types and Structures

Primitives

# Numbers
int_num = 100
float_num = 10.5
 
# Strings
my_string = "Hello, World!"
 
# Booleans
is_true = True
is_false = False

Data Structures

Lists: Ordered, mutable collections.

my_list = [1, "apple", 3.14]
my_list.append("banana")
print(my_list[1])  # 'apple'

Tuples: Ordered, immutable collections.

my_tuple = (1, "apple", 3.14)
print(my_tuple[0]) # 1

Dictionaries: Unordered, mutable key-value pairs.

my_dict = {"name": "Bob", "age": 25}
print(my_dict["name"]) # 'Bob'
my_dict["city"] = "New York"

Sets: Unordered, mutable collections of unique elements.

my_set = {1, 2, 3, 3, 4}
# my_set is {1, 2, 3, 4}
my_set.add(5)

Operators

Arithmetic

5 + 2  # Addition -> 7
5 - 2  # Subtraction -> 3
5 * 2  # Multiplication -> 10
5 / 2  # Division -> 2.5
5 // 2 # Floor Division -> 2
5 % 2  # Modulus -> 1
5 ** 2 # Exponentiation -> 25

Comparison

a, b = 5, 10
a == b # False
a != b # True
a > b  # False
a <= b # True

Logical

(5 > 2) and (10 > 5) # True
(5 > 2) or (5 > 10)  # True
not (5 > 2)          # False

Control Flow

Conditional Statements

score = 85
if score >= 90:
    print("A")
elif score >= 80:
    print("B")
else:
    print("C")
# Output: B

Loops

For Loop: Iterates over a sequence.

for i in range(5): # 0 to 4
    print(i)
 
for fruit in ["apple", "banana"]:
    print(fruit)

While Loop: Executes as long as a condition is true.

count = 0
while count < 5:
    print(count)
    count += 1

Functions

Functions are defined with the def keyword.

def greet(name):
    """A function to greet someone."""
    return f"Hello, {name}!"
 
message = greet("World")
print(message) # "Hello, World!"

List Comprehensions

A concise way to create lists.

# Create a list of squares from 0 to 9
squares = [x**2 for x in range(10)]
# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
 
# Create a list of even numbers
evens = [x for x in range(10) if x % 2 == 0]
# [0, 2, 4, 6, 8]

Working with Files

Using with is recommended as it handles closing the file automatically.

# Writing to a file
with open("file.txt", "w") as f:
    f.write("Hello, file!\n")
 
# Reading from a file
with open("file.txt", "r") as f:
    content = f.read()
    print(content)

Exception Handling

Handle errors gracefully using try...except blocks.

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")
finally:
    print("Execution finished.")