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Format CLI help text in Python
Build a readable usage string for a command-line tool, aligning flags and wrapping descriptions with the textwrap module.
import textwrap
def format_help(command_name: str, description: str, options: list[tuple[str, str]]) -> str:
"""Format CLI help text into a readable usage string."""
header = f"Usage: {command_name} [OPTIONS]"
lines = [header, "", description, "", "Options:"]
for flag, help_text in options:
…How to Add a Dry Run Flag to a Python CLI Command
Build a Python CLI command with a --dry-run flag that previews actions and exits before making real changes.
import argparse
import sys
def main():
parser = argparse.ArgumentParser(description="Sample CLI command with dry-run flag")
parser.add_argument("--name", required=True, help="Name to greet")
parser.add_argument("--dry-run", action="store_true", dest="dry_run",
help="Show what would…How to Parse Command Line Arguments in Python with argparse
Build a CLI that accepts positional integers, an optional --sum flag, and a --verbose switch, all with Python's standard argparse library.
import argparse
def main():
parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument('numbers', metavar='N', type=int, nargs='+',
help='an integer for the accumulator')
parser.add_argument('--sum', dest='accumulate', action='store_const',
…How to Print Colored Text in Python with ANSI Codes
Define a small Colors class and a colored() helper to print styled terminal text using ANSI escape codes.
class Colors:
RESET = "\033[0m"
RED = "\033[31m"
GREEN = "\033[32m"
YELLOW = "\033[33m"
BLUE = "\033[34m"
MAGENTA = "\033[35m"
CYAN = "\033[36m"
WHITE = "\033[37m"
BOLD = "\033[1m"
UNDERLINE = "\033[4m"
def colored(text, color):
return f"{color}{text}{Colors.RESET}"
if _…How to Read Environment Variables in Python with Default Values
Retrieve an environment variable safely using os.getenv() with a fallback default when the variable is missing.
import os
database_url = os.getenv("DATABASE_URL", "postgresql://localhost:5432/mydb")
print(f"Database URL: {database_url}")How to Validate CLI Integer Option Within a Range in Python
Use argparse with integer type and bounds checking to validate a command-line option falls within a specified min-max range.
import argparse
def main():
parser = argparse.ArgumentParser(description="Validate an integer within a range.")
parser.add_argument("--value", type=int, required=True, help="Integer to validate")
parser.add_argument("--min", type=int, default=0, help="Minimum allowed value")
parser.add_argument("--max…How to Mock a Failing Dependency to Test Error Paths in Python
Inject a fake HTTP client that raises a connection error to test how code handles dependency failures without touching the network.
import requests
def fetch_user(user_id):
url = f"https://api.example.com/users/{user_id}"
response = requests.get(url, timeout=5)
response.raise_for_status()
return response.json()
def get_user_name(user_id, http_client):
try:
user_data = http_client(user_id)
return user_data["nam…Build a Command-Line To-Do List Application with Data Persistence in Python
A persistent command-line to-do list that saves tasks as JSON, supporting add, show, toggle done, and quit commands.
import json
import os
TODO_FILE = "todos.json"
def load_todos():
if not os.path.exists(TODO_FILE):
return []
with open(TODO_FILE, "r") as f:
return json.load(f)
def save_todos(todos):
with open(TODO_FILE, "w") as f:
json.dump(todos, f, indent=2)
def show_todos(todos):
if not…Find k Closest Points to Origin in Python
Sorts a list of (x, y) point tuples by their Euclidean distance from the origin and returns the k nearest points.
import math
def k_closest(points, k):
points.sort(key=lambda p: math.sqrt(p[0]**2 + p[1]**2))
return points[:k]
if __name__ == "__main__":
points = [(1, 2), (3, 4), (-1, 0), (5, 5), (0, 1)]
k = 3
result = k_closest(points, k)
print(f"Original points: {points}")
print(f"K closest points (k…How to Compute Cosine Similarity Between Two Vectors in Python
This code calculates the cosine similarity between two numeric vectors using the dot product and Euclidean norms, returning a value between -1 and 1.
import math
def cosine_similarity(vec_a, vec_b):
if len(vec_a) != len(vec_b):
raise ValueError("Vectors must have the same length")
dot_product = sum(a * b for a, b in zip(vec_a, vec_b))
norm_a = math.sqrt(sum(a * a for a in vec_a))
norm_b = math.sqrt(sum(b * b for b in vec_b))
i…Pair Elements with Next Cyclic Neighbor in Python
Create tuples pairing every element with its next element, wrapping around to the first element for the last one.
def cyclic_pairs(lst):
if not lst:
return []
return [(lst[i], lst[(i + 1) % len(lst)]) for i in range(len(lst))]
if __name__ == "__main__":
sample = [1, 2, 3, 4, 5]
result = cyclic_pairs(sample)
print(result)Cycle an iterable forever in Python
Define a generator that repeatedly yields items from an iterable, cycling back to the beginning infinitely.
def cycle_generator(iterable):
"""Yield items from iterable forever, cycling back to the start."""
items = list(iterable) # Convert to list so it can restart
index = 0
while True:
yield items[index]
index = (index + 1) % len(items)
if __name__ == "__main__":
colors = ["red", "gre…How to Mock an LLM Client in Python
Create a simple mock LLM client that returns a canned completion for testing or development without a real API.
from dataclasses import dataclass
@dataclass
class MockLLMClient:
canned_response: str = "This is a canned completion."
def complete(self, prompt: str) -> str:
return f"{self.canned_response} [to: {prompt[:20]}]"
if __name__ == "__main__":
client = MockLLMClient()
result = client.complete(…Build a Live Countdown Timer for Events in Python
A Python script that displays a real-time countdown to a target date and time, updating every second in the console.
import datetime
import time
def countdown(event_name, target_datetime):
"""Displays a live countdown to a target datetime."""
while True:
now = datetime.datetime.now()
remaining = target_datetime - now
if remaining.total_seconds() <= 0:
print(f"\n🚀 {event_name} is happening…How to Build a CLI with argparse in Python
Create a beginner-friendly command-line tool in Python that processes multiple filenames with optional flags for verbose output and uppercase conversion.
import argparse
def main():
parser = argparse.ArgumentParser(
description="A simple CLI to process files with optional verbose mode."
)
parser.add_argument("filenames", nargs="+", help="Files to process")
parser.add_argument("-v", "--verbose", action="store_true", help="Print extra details")
…How to Build a Docker Image Tag Script in Python
Generate consistent Docker image tags from service names and versions with automatic normalization.
#!/usr/bin/env python3
"""Mock script for building docker image tags."""
def build_tag(service_name: str, version: str, registry: str = "docker.io") -> str:
"""Construct a docker image tag."""
safe_name = service_name.lower().replace("_", "-")
return f"{registry}/{safe_name}:{version}"
if __name__ == "…How to Build a Python argparse CLI for Beginners
Build a beginner-friendly command-line interface using Python's argparse module with positional and optional arguments.
import argparse
def greet(name, greeting="Hello", uppercase=False):
message = f"{greeting}, {name}!"
if uppercase:
message = message.upper()
return message
def main():
parser = argparse.ArgumentParser(description="A simple CLI greet tool for beginners.")
parser.add_argument("name", help="…How to Build a Simple Python CLI with argparse
Create a friendly command-line greeting tool with argparse that accepts a positional name and optional flags for custom greetings and uppercase output.
import argparse
def greet(name, greeting="Hello", uppercase=False):
message = f"{greeting}, {name}!"
return message.upper() if uppercase else message
if __name__ == "__main__":
parser = argparse.ArgumentParser(
description="A simple greeting tool to demonstrate argparse basics."
)
parser.…How to Build a Simple argparse CLI in Python
Create a beginner-friendly command-line tool with argparse that reads a file, optionally uppercases its lines, and prints a configurable number of lines.
import argparse
def main():
parser = argparse.ArgumentParser(
description="Automate file processing with a simple CLI tool."
)
parser.add_argument("filename", help="Path to the input file")
parser.add_argument("--uppercase", action="store_true", help="Convert text to uppercase")
parser.add…How to Build a Simple argparse CLI in Python
Build a beginner-friendly command-line tool with argparse that greets a user, with optional greeting text and uppercase output.
import argparse
def greet(name, greeting="Hello", uppercase=False):
message = f"{greeting}, {name}!"
if uppercase:
message = message.upper()
return message
if __name__ == "__main__":
parser = argparse.ArgumentParser(description="Simple CLI greeting tool")
parser.add_argument("name", help=…How to Build an argparse CLI That Filters File Lines by Keyword in Python
This Python script is a command-line tool built with argparse that reads a text file and prints only the lines that contain (or don't contain) a given keyword.
import argparse
import sys
def main():
parser = argparse.ArgumentParser(description="Filter lines from a file by keyword.")
parser.add_argument("input", type=str, help="File to read")
parser.add_argument("keyword", type=str, help="Keyword to filter lines")
parser.add_argument("--contains", action="sto…How to Build an argparse Command-Line Tool in Python
Create a simple file-info CLI with argparse that counts lines and prints file size, with optional verbose and output flags.
import argparse
import os
from pathlib import Path
def process_file(filepath, verbose=False):
"""Read a file and report its size and line count."""
path = Path(filepath)
if not path.exists():
raise FileNotFoundError(f"File not found: {filepath}")
content = path.read_text()
lines = conten…How to Create a Simple Python CLI with argparse
Build a beginner-friendly command-line tool with argparse that accepts positional and optional arguments to greet users flexibly.
import argparse
def greet(name, greeting="Hello", uppercase=False):
message = f"{greeting}, {name}!"
return message.upper() if uppercase else message
def main():
parser = argparse.ArgumentParser(
description="A simple CLI tool that greets users."
)
parser.add_argument(
"name",
…How to Decrypt a GPG File with a Passphrase in Python
Decrypt a GPG-encrypted file using a passphrase via the gpg CLI wrapped in a reusable Python function.
import subprocess
import tempfile
from pathlib import Path
def decrypt_gpg_file(input_file: str, passphrase: str) -> str:
"""Decrypt a GPG file using a passphrase and return the plaintext."""
result = subprocess.run(
["gpg", "--batch", "--yes", "--passphrase", passphrase, "--decrypt", input_file],
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