Introduction

Python is a popular and easy-to-learn programming language. It is used in many fields such as web development, data analysis, automation, artificial intelligence, and more. This cheatsheet covers the most important and commonly used concepts in Python. It is helpful for beginners and also for experienced developers who want to revise the basics quickly.

1. Variables

  
    name = "Alice"
age = 25

2. Data Types

  
    num = 10             # int
price = 5.5          # float
name = "Tom"         # str
is_valid = True      # bool

3. Lists

  
    fruits = ["apple", "banana", "cherry"]
fruits.append("orange")
print(fruits[1])  # banana

4. Tuples

  
    colors = ("red", "green", "blue")
print(colors[0])  # red

5. Dictionaries

  
    student = {"name": "John", "age": 20}
print(student["name"])  # John

6. Sets

  
    nums = {1, 2, 3, 2}
print(nums)  # {1, 2, 3}

7. Conditional Statements

  
    age = 18
if age >= 18:
    print("Adult")
else:
    print("Minor")

8. Loops

  
    for i in range(5):
    print(i)
  
  
    count = 0
while count < 5:
    print(count)
    count += 1

9. Functions

  
    def greet(name):
    print("Hello", name)

greet("Alice")

10. Classes and Objects

  
    class Person:
    def __init__(self, name):
        self.name = name

    def say_hello(self):
        print("Hi, I am", self.name)

p = Person("David")
p.say_hello()

11. Exception Handling

  
    try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero")

12. List Comprehension

  
    squares = [x*x for x in range(5)]
print(squares)  # [0, 1, 4, 9, 16]

13. Importing Modules

  
    import math
print(math.sqrt(16))  # 4.0

14. File Handling

  
    with open("file.txt", "r") as f:
    content = f.read()
  
  
    with open("file.txt", "w") as f:
    f.write("Hello, world")

15. Lambda Functions

  
    add = lambda x, y: x + y
print(add(3, 5))  # 8

16. Map, Filter, Reduce

  
    nums = [1, 2, 3]
squared = list(map(lambda x: x*x, nums))
  
  
    even = list(filter(lambda x: x % 2 == 0, nums))
  
  
    from functools import reduce
total = reduce(lambda x, y: x + y, nums)

17. Global and Local Variables

  
    x = 10  # global

def test():
    y = 5  # local
    print(x + y)

test()

18. String Formatting

  
    name = "Tom"
age = 20
print(f"My name is {name} and I am {age} years old.")

19. Type Conversion

  
    x = "123"
y = int(x)  # converts to integer

20. Built-in Functions

21. Enumerate

  
    colors = ["red", "green", "blue"]
for index, color in enumerate(colors):
    print(index, color)

22. Zip

  
    names = ["Alice", "Bob"]
scores = [85, 90]
for name, score in zip(names, scores):
    print(name, score)

23. Docstrings

  
    def greet():
    """This function prints a greeting"""
    print("Hello")

24. args and kwargs

  
    def add(*args):
    return sum(args)

def show(**kwargs):
    print(kwargs)

add(1, 2, 3)
show(name="Tom", age=30)

25. Virtual Environment (venv)

  
    python -m venv env

26. List Methods

  
    a = [1, 2, 3]
a.append(4)
a.remove(2)
a.pop()
a.sort()
a.reverse()

27. Dictionary Methods

  
    d = {"a": 1, "b": 2}
d.keys()
d.values()
d.items()
d.get("a")

28. Comprehensions with Conditions

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

29. Range

  
    range(5)         # 0 to 4
range(1, 6)      # 1 to 5
range(1, 10, 2)  # step by 2

30. Type Hints (Python 3.5+)

  
    def add(x: int, y: int) -> int:
    return x + y

31. Unpacking

  
    a, b = [1, 2]

32. Ternary Operator

  
    result = "Yes" if x > 5 else "No"

33. Chained Comparisons

  
    x = 10
if 5 < x < 15:
    print("x is between 5 and 15")

34. Generators

  
    def count_up_to(n):
    i = 1
    while i <= n:
        yield i
        i += 1

35. Decorators

  
    def decorator(func):
    def wrapper():
        print("Before")
        func()
        print("After")
    return wrapper

@decorator
def greet():
    print("Hello")

greet()

36. Context Manager (with statement)

  
    with open("file.txt") as f:
    data = f.read()

37. Assertions

  
    x = 5
assert x > 0, "x must be positive"

38. The __name__ == "__main__" Block

  
    if __name__ == "__main__":
    print("Running directly")

39. Using pass , break , continue

  
    for i in range(5):
    if i == 3:
        continue
    print(i)

40. Global Keyword

  
    x = 10

def modify():
    global x
    x = 20

41. is vs ==

  
    a = [1, 2]
b = [1, 2]
print(a == b)  # True
print(a is b)  # False

42. Python Comments

  
    """
This is
a multiline comment
"""

43. Command Line Arguments with sys.argv

  
    import sys
print(sys.argv[1])  # First command-line argument

44. Using dir() and help()

  
    dir(str)
help(str)

45. Using __init__ and __str__ in Classes

  
    class Car:
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return f"Car name: {self.name}"

46. Private Variables (by Convention)

  
    class Example:
    def __init__(self):
        self._protected = "Warning only"
        self.__private = "Strongly private"

47. Python Slicing

  
    text = "abcdef"
print(text[1:4])   # 'bcd'
print(text[:3])    # 'abc'
print(text[::-1])  # reverse string

48. Set Operations

  
    a = {1, 2, 3}
b = {3, 4, 5}
print(a.union(b))        # {1, 2, 3, 4, 5}
print(a.intersection(b)) # {3}
print(a.difference(b))   # {1, 2}

49. Using all() and any()

  
    nums = [1, 2, 3]
print(all(x > 0 for x in nums))  # True
print(any(x > 2 for x in nums))  # True

50. Chained Function Calls

  
    def add(x):
    return x + 1

def multiply(x):
    return x * 2

print(multiply(add(3)))  # 8

51. NamedTuple (from collections )

  
    from collections import namedtuple
Point = namedtuple("Point", "x y")
p = Point(1, 2)
print(p.x, p.y)

52. Defaultdict

  
    from collections import defaultdict
d = defaultdict(int)
d["a"] += 1
print(d)  # defaultdict(<class 'int'>, {'a': 1})

53. Counter

  
    from collections import Counter
c = Counter("banana")
print(c)  # {'a': 3, 'n': 2, 'b': 1}

54. Date and Time

  
    import datetime
now = datetime.datetime.now()
print(now.strftime("%Y-%m-%d %H:%M"))

55. Regular Expressions (Regex)

  
    import re
text = "abc123"
match = re.search(r"\d+", text)
print(match.group())  # 123

56. JSON Handling

  
    import json
data = {"name": "Tom", "age": 20}
json_str = json.dumps(data)
parsed = json.loads(json_str)

57. Using __slots__ (Memory Optimization in Classes)

  
    class Person:
    __slots__ = ['name', 'age']
    def __init__(self, name, age):
        self.name = name
        self.age = age

58. Using type() to Create Classes Dynamically

  
    MyClass = type("MyClass", (object,), {"x": 5})
obj = MyClass()
print(obj.x)

59. Using eval() and exec()

  
    x = 10
print(eval("x + 5"))  # 15

⚠️ Avoid using eval() or exec() with user input due to security risks.

60. Unit Testing (with unittest )

  
    import unittest

class TestAdd(unittest.TestCase):
    def test_sum(self):
        self.assertEqual(2 + 3, 5)

if __name__ == "__main__":
    unittest.main()

Conclusion

If you're serious about mastering Python:

This is now a complete Python cheatsheet for practical use, projects, interviews, and continued learning.