Cheatsheet#
This page contains Python Beginner’s Cheatsheet, a short list with some hidden Gems
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String Operations You Might Not Know
# Remove whitespace from both ends
text = " hello "
text.strip() # "hello"
# Center text in a fixed width
"Python".center(10, "*") # "**Python**"
# Split string into fixed-width chunks
chunks = [text[i:i+3] for i in range(0, len(text), 3)]
List Tricks
# Create a list of numbers easily
numbers = list(range(1, 11)) # [1, 2, 3, ..., 10]
# Get last n items
my_list = [1, 2, 3, 4, 5]
last_three = my_list[-3:] # [3, 4, 5]
# Remove duplicates while maintaining order
my_list = list(dict.fromkeys(my_list))
Dictionary Magic
# Get value with fallback if key doesn't exist
my_dict = {'a': 1}
value = my_dict.get('b', 'not found') # 'not found'
# Merge dictionaries
dict1 = {'a': 1}
dict2 = {'b': 2}
merged = {**dict1, **dict2} # {'a': 1, 'b': 2}
Loop Enhancements
# Enumerate with custom start index
for i, item in enumerate(['a', 'b', 'c'], start=1):
print(f"{i}: {item}") # 1: a, 2: b, 3: c
# Loop over multiple lists simultaneously
for x, y in zip([1, 2, 3], ['a', 'b', 'c']):
print(f"{x}-{y}") # 1-a, 2-b, 3-c
File Operations
# Read file directly into a list of lines
with open('file.txt') as f:
lines = f.read().splitlines()
# Write multiple lines at once
lines = ['line1', 'line2', 'line3']
with open('file.txt', 'w') as f:
f.write('\n'.join(lines))
Built-in Functions You Should Know
# Convert multiple inputs to integers
x, y, z = map(int, input().split())
# Find largest/smallest n items
import heapq
numbers = [10, 5, 8, 3, 1]
largest_three = heapq.nlargest(3, numbers) # [10, 8, 5]
String Formatting
# f-strings with formatting
name = "Alice"
age = 25.5
print(f"{name:>10}") # Right align with width 10
print(f"{age:.1f}") # One decimal place
# Format numbers with commas
number = 1000000
print(f"{number:,}") # 1,000,000
Collection Operations
from collections import Counter, defaultdict
# Count occurrences
text = "hello world"
letter_count = Counter(text) # {'l': 3, 'o': 2, ...}
# Dictionary with default value
d = defaultdict(list)
d['new_key'].append(1) # No KeyError if key doesn't exist
Conditional Assignments
# Ternary operator
x = 5
status = "even" if x % 2 == 0 else "odd"
# Multiple conditions
grade = "A" if score >= 90 else "B" if score >= 80 else "C"
Error Handling
# Multiple exception types
try:
# some code
except (TypeError, ValueError) as e:
print(f"Error: {e}")
# Else clause in try-except
try:
result = perform_operation()
except Exception:
print("Error occurred")
else:
print("Operation successful!")
finally:
print("Cleanup code")
Context Managers
# Custom context manager
from contextlib import contextmanager
@contextmanager
def timer():
from time import time
start = time()
yield
print(f"Elapsed: {time() - start:.2f} seconds")
with timer():
# Your code here
pass
PRO Tips
Use help() function to get documentation
Try dir() to see all attributes of an object
The interactive interpreter can be cleared with ctrl + l
Use _` to access the last printed expression in interactive mode
IPython’s ? and ?? for quick help and source code
Links#
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