Python Basic Syntax Cheat Sheet

A concise reference for Python beginners and developers coming from languages like JavaScript, Java, or C++.

1. Variables & Data Types

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x = 10              # int
y = 3.14            # float
name = "Alice"      # string
is_valid = True     # boolean
items = [1, 2, 3]   # list
data = {"a": 1}     # dict
nums = (1, 2, 3)    # tuple
unique = {1, 2, 3}  # set

Type Checking

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type(x)        # <class 'int'>
isinstance(x, int)  # True

2. Control Flow

If / Elif / Else

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if x > 10:
    print("Large")
elif x == 10:
    print("Equal")
else:
    print("Small")

Ternary Expression

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msg = "even" if x % 2 == 0 else "odd"

3. Loops

For Loop

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for i in range(5):       # 0,1,2,3,4
    print(i)

for item in items:        # iterate over list
    print(item)

While Loop

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while x > 0:
    print(x)
    x -= 1

Break / Continue

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for i in range(5):
    if i == 2:
        continue
    if i == 4:
        break
    print(i)

4. Functions

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def greet(name):
    return f"Hello, {name}!"

print(greet("Wen"))

Default & Keyword Arguments

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def power(base, exp=2):
    return base ** exp

print(power(3))       # 9
print(power(exp=3, base=2))  # 8

Lambda (Anonymous Function)

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square = lambda x: x ** 2
print(square(4))  # 16

5. Collections (List / Dict / Set / Tuple)

List

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nums = [1, 2, 3]
nums.append(4)
nums.extend([5, 6])
nums.insert(1, 100)
nums.pop()
nums.remove(100)
print(nums[::-1])     # reverse

Dictionary

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person = {"name": "Alice", "age": 25}
print(person["name"])
person["city"] = "Sydney"

for key, value in person.items():
    print(key, value)

Set

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

Tuple

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point = (10, 20)
x, y = point  # unpacking

6. List Comprehensions

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squares = [x**2 for x in range(5)]
even = [x for x in range(10) if x % 2 == 0]

7. String Operations

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s = "Python"
print(s.lower())
print(s.upper())
print(s.replace("Py", "My"))
print(s[0:3])   # slicing
print("Hello " + s)
print(f"Welcome to {s}!")

8. Classes & Objects

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

    def greet(self):
        return f"Hi, I'm {self.name}!"

p = Person("Alice", 25)
print(p.greet())

9. File I/O

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with open("data.txt", "w") as f:
    f.write("Hello, file!")

with open("data.txt", "r") as f:
    content = f.read()
    print(content)

10. Common Built-in Functions

Function Description Example
len() length len([1,2,3]) → 3
sum() sum of elements sum([1,2,3]) → 6
max(), min() largest/smallest max([1,5,3]) → 5
sorted() return sorted list sorted([3,1,2]) → [1,2,3]
enumerate() get index + value for i,v in enumerate(arr)
zip() combine iterables zip([1,2], ['a','b']) → [(1,'a'), (2,'b')]
map() apply function map(str, [1,2,3]) → ['1','2','3']
filter() filter items filter(lambda x: x>0, nums)

11. Error Handling

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try:
    x = 10 / 0
except ZeroDivisionError as e:
    print("Cannot divide by zero!")
finally:
    print("Done.")

12. Imports & Modules

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import math
from datetime import datetime

print(math.sqrt(16))
print(datetime.now())

13. Useful One-liners

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# Swap values
a, b = b, a

# Read input
name = input("Enter name: ")

# Check membership
if "x" in [1, "x", 3]:
    print("Found!")

# Conditional expression
status = "OK" if success else "FAILED"

14. Comments & Docstrings

Single-line comment

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"""
Multi-line comment or docstring
Use triple quotes for documentation.
"""