Cheatsheet

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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

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