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Python Basics Cheat Sheet
programmingGrades 8-129 sections
Visual Overview: Python Type Hierarchy
All Python objects inherit from the base object class and branch into major type categories
Data Types & Variables
Type
Example
Notes
int
x = 42
Unlimited precision
float
x = 3.14
Decimal numbers
str
x = "hello"
Immutable sequences
bool
x = True
True or False
list
x = [1, 2, 3]
Mutable, ordered
tuple
x = (1, 2, 3)
Immutable, ordered
dict
x = {"a": 1}
Key-value pairs
set
x = {1, 2, 3}
Unique, unordered
Type Casting: int(), str(), float(), bool(), list(), tuple()
String Methods
Method
Example
Output
upper()
"hello".upper()
"HELLO"
lower()
"HELLO".lower()
"hello"
strip()
" hi ".strip()
"hi"
split()
"a,b,c".split(",")
["a", "b", "c"]
join()
"-".join(["a","b"])
"a-b"
replace()
"hi".replace("i","o")
"ho"
find()
"hello".find("l")
2
startswith()
"hello".startswith("he")
True
Loops & Control Flow
# if-elif-else
if x > 0:
print("positive")
elif x < 0:
print("negative")
else:
print("zero")
# for loop
for i in range(5):
print(i) # 0,1,2,3,4
# while loop
while x > 0:
print(x)
x -= 1
# break and continue
for i in range(10):
if i == 3:
continue
if i == 7:
break
print(i)
Functions
# Basic function
def greet(name):
return f"Hello, {name}!"
# Default arguments
def add(a, b=0):
return a + b
# *args (variable positional)
def sum_all(*numbers):
return sum(numbers)
# **kwargs (variable keyword)
def print_info(**kwargs):
for key, value in kwargs.items():
print(f"{key}: {value}")
# Lambda (anonymous)
square = lambda x: x**2
print(square(5)) # 25
List Comprehensions
# Basic list comprehension
squares = [x**2 for x in range(5)]
# [0, 1, 4, 9, 16]
# With condition (filter)
evens = [x for x in range(10) if x % 2 == 0]
# [0, 2, 4, 6, 8]
# Nested comprehension
matrix = [[i+j for j in range(3)] for i in range(3)]
# Dictionary comprehension
squares_dict = {x: x**2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
# Set comprehension
unique_chars = {char for word in words for char in word}
File I/O & Exception Handling
# File operations
with open("file.txt", "r") as f:
content = f.read() # entire file
lines = f.readlines() # list of lines
# Write to file
with open("file.txt", "w") as f:
f.write("Hello")
# Exception handling
try:
result = 10 / 0
except ZeroDivisionError:
print("Cannot divide by zero!")
except Exception as e:
print(f"Error: {e}")
finally:
print("Cleanup code")
Useful Built-in Functions
Function
Example
Output
len()
len([1,2,3])
3
max()
max([3,1,4])
4
min()
min([3,1,4])
1
sum()
sum([1,2,3])
6
abs()
abs(-5)
5
round()
round(3.7)
4
sorted()
sorted([3,1,2])
[1,2,3]
enumerate()
enumerate(["a","b"])
Index-value pairs
zip()
zip([1,2], ["a","b"])
[(1,"a"),(2,"b")]
map()
map(str, [1,2])
["1","2"]
String Formatting
# f-strings (Python 3.6+)
name = "Raj"
age = 16
print(f"I am {name}, {age} years old")
# format() method
"Hello, {}!".format("world")
"{1} {0}".format("world", "Hello")
"{name} is {age}".format(name="Priya", age=15)
# Old-style % formatting (legacy)
"Hello %s" % "world"
# Alignment and padding
f"{name:>10}" # Right-align in 10 chars
f"{age:05d}" # Zero-pad to 5 digits
f"{3.14159:.2f}" # Round to 2 decimals