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How to Convert and Process Text in Python
This code cleans, converts, splits, joins, counts, replaces, reverses, and finds substrings in a text string using Python's standard string methods.
text = " hello world, python is fun! "
# Clean up whitespace
cleaned = text.strip()
# Convert to title case
titled = cleaned.title()
# Split into words
words = cleaned.split()
# Join with hyphens
hyphenated = "-".join(words)
# Count occurrences of a letter
letter_count = cleaned.count("o")
# Replace a word
rep…How to Sort Text in Python with a Simple Helper Function
A compact helper function that sorts a list of strings or splits a string into words and sorts them alphabetically, with optional reverse ordering.
def sort_text(data, reverse=False):
"""
Sort a list of strings (or a single string split into words) alphabetically.
"""
if isinstance(data, str):
words = data.split()
else:
words = [str(item) for item in data]
return sorted(words, reverse=reverse)
if __name__ == "__main__":
…Python String Helper Functions for Beginners
A set of beginner-friendly Python functions that count words, reverse text, convert to title case, strip punctuation, and compute character frequency from a string.
def count_words(text):
"""Count the number of words in a string."""
return len(text.split())
def reverse_text(text):
"""Reverse the entire string."""
return text[::-1]
def title_case(text):
"""Capitalize the first letter of each word."""
return text.title()
def remove_punctuation(text):
…Reverse Words in a Sentence While Keeping Punctuation in Python
Reverses the order of words in a sentence while leaving punctuation and spaces in their original positions using Python's re module.
def reverse_words_preserving_punctuation(sentence: str) -> str:
import re
# Split into words and punctuation tokens
tokens = re.findall(r'\w+|[^\w\s]|\s+', sentence)
words = [t for t in tokens if re.fullmatch(r'\w+', t)]
words.reverse()
result_parts = []
word_index = 0
for token in toke…String helpers in Python: stats, reverse, and remove vowels
Three beginner-friendly Python functions compute text statistics, reverse word order, and strip vowels from a string.
def text_stats(text: str) -> dict:
"""Return basic statistics for a given text string."""
words = text.split()
return {
"characters": len(text),
"words": len(words),
"sentences": text.count(".") + text.count("!") + text.count("?"),
"uppercase": sum(1 for c in text if c.isupp…How to Reverse a List in Place Without Using reverse() in Python
A two-pointer while loop swaps elements from both ends toward the center to reverse a list in place without creating a copy.
def reverse_list_in_place(lst):
left = 0
right = len(lst) - 1
while left < right:
lst[left], lst[right] = lst[right], lst[left]
left += 1
right -= 1
if __name__ == "__main__":
my_list = [1, 2, 3, 4, 5]
print("Original:", my_list)
reverse_list_in_place(my_list)
prin…How to Build a Two-Way Dictionary in Python
Implement a BiDict class that supports both forward key-to-value and reverse value-to-key lookups with a simple add, delete, and update API.
class BiDict:
def __init__(self, data=None):
self.forward = {}
self.backward = {}
if data:
self.update(data)
def update(self, data):
for key, value in data.items():
self[key] = value
def __setitem__(self, key, value):
self.forward[key] = val…How to Invert a Dictionary in Python Safely
Swap dictionary keys and values while detecting duplicate values to prevent silent data loss.
def invert_dict_safely(d):
inverted = {}
for key, value in d.items():
if value not in inverted:
inverted[value] = key
else:
raise ValueError(f"Duplicate value '{value}' would cause data loss")
return inverted
if __name__ == "__main__":
sample = {"a": 1, "b": 2,…Find the Last Index Where a Condition Is True in Python
This code scans a sequence from the end and returns the index of the last element that satisfies a given condition, or -1 if none do.
def last_index_where(sequence, condition):
"""Return the index of the last element in sequence that satisfies condition."""
for i in range(len(sequence) - 1, -1, -1):
if condition(sequence[i]):
return i
return -1
if __name__ == "__main__":
numbers = [1, 4, 7, 2, 9, 5, 8, 3]
is_…How to Evaluate RPN Expressions in Python
Use a stack to evaluate Reverse Polish Notation token lists with a dictionary of operator lambdas, truncating division toward zero.
def eval_rpn(tokens):
stack = []
ops = {
'+': lambda a, b: a + b,
'-': lambda a, b: a - b,
'*': lambda a, b: a * b,
'/': lambda a, b: int(a / b) # truncate toward zero
}
for token in tokens:
if token in ops:
b = stack.pop()
a = stack.pop(…How to Sort Command-Line Arguments in Python
Build a beginner-friendly argparse CLI that sorts numbers or words passed as arguments, with an optional reverse flag.
import argparse
def main():
parser = argparse.ArgumentParser(description="Sort numbers or words from the command line.")
parser.add_argument("items", nargs="+", help="Items to sort (numbers or words)")
parser.add_argument("--reverse", "-r", action="store_true", help="Sort in descending order")
args =…How to Mock open() in Python Using unittest.mock.patch
This code shows how to use unittest.mock.patch with mock_open to test a function that checks if a Git patch can be reverse-applied by reading file content.
import unittest
from unittest.mock import patch, mock_open
def apply_reverse_check(file_path, expected_patch):
"""
Check if a patch can be reverse-applied by comparing file content
with the expected patch's reverse result.
"""
try:
with open(file_path, "r") as f:
content = f.r…How to Test Properties with Random Inputs in Python
Write a simple property-based test in Python using random string generation to verify that string invariants like reverse-twice identity and uppercase idempotence always hold.
import random
import string
def generate_random_string(length: int) -> str:
"""Generate a random alphanumeric string of given length."""
chars = string.ascii_letters + string.digits
return "".join(random.choice(chars) for _ in range(length))
def reverse_twice_is_identity(s: str) -> bool:
"""Propert…Python Saga Compensating Steps Mock
Mock a distributed transaction saga with forward steps and compensating actions that reverse partial progress on failure.
from datetime import datetime
def make_payment(user_id, amount):
print(f"[{datetime.now():%H:%M:%S}] Payment of ${amount} processed for user {user_id}")
return {"step": "payment", "status": "ok", "details": f"${amount} charged"}
def deduct_inventory(order_id, items):
print(f"[{datetime.now():%H:%M:%S}]…How to Mock a Cross-Shard Saga in Python
Simulate a distributed saga with compensating transactions across multiple database shards using a lightweight Python class that tracks executed steps and rolls them back in reverse on failure.
import json
class SagaState:
def __init__(self, saga_id):
self.saga_id = saga_id
self.executed_steps = []
self.compensations = []
def execute_step(self, shard, step_name, operation):
self.executed_steps.append((shard, step_name))
print(f"[Saga {self.saga_id}] Executin…Browse by section
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