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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
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 Parse CLI Arguments in Python with argparse
Build a beginner-friendly CLI with argparse that accepts optional --name, --greeting, and --uppercase flags, then prints a customizable greeting.
import argparse
def main():
parser = argparse.ArgumentParser(description="Greet a user with optional customization.")
parser.add_argument("--name", default="world", help="Name to greet")
parser.add_argument("--greeting", default="Hello", help="Greeting word")
parser.add_argument("--uppercase", action=…Fix and Test a Regression Bug in Python with Unit Tests
This code implements a circle area function that raises ValueError for negative radii, then runs basic tests and a regression check for that edge case.
import math
def calculate_area(radius):
"""Calculate the area of a circle given its radius."""
if radius < 0:
raise ValueError("Radius cannot be negative")
return math.pi * radius ** 2
def main():
test_cases = [0, 1, 2.5, 5, 10]
print("Circle Area Calculator")
print("-" * 30)
…How to Parametrize pytest Tests with Multiple Input Cases in Python
This code shows how to use pytest's @pytest.mark.parametrize decorator to run the same test function across multiple input-output combinations, checking that an add function behaves correctly for each case.
import pytest
def add(a, b):
return a + b
@pytest.mark.parametrize("a,b,expected", [
(1, 2, 3),
(5, 5, 10),
(-1, 1, 0),
(0, 0, 0),
(10, -3, 7),
])
def test_add(a, b, expected):
assert add(a, b) == expected
if __name__ == "__main__":
pytest.main([__file__, "-v"])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…How to Use setUp and tearDown in Python unittest TestCase
Demonstrates how to structure unit tests with setUp and tearDown methods in Python's unittest framework for reusable test fixtures.
import unittest
class ExampleTest(unittest.TestCase):
def setUp(self):
self.data = [1, 2, 3]
def tearDown(self):
self.data = None
def test_length(self):
self.assertEqual(len(self.data), 3)
def test_contains(self):
self.assertIn(2, self.data)
if __name__ == "__main…How to use Optional type hint in Python
Use the Optional type hint to indicate a parameter can be a string or None, with an example function that handles both cases.
from typing import Optional
def greet(name: Optional[str]) -> str:
if name is None:
return "Hello, anonymous!"
else:
return f"Hello, {name}!"
if __name__ == "__main__":
print(greet("Alice"))
print(greet(None))Table-Driven Tests in Python (unittest)
Run a single unittest test against many input cases using a list of tuples and subTest.
import unittest
def add(a, b):
return a + b
class TestAddFunction(unittest.TestCase):
def test_add_with_table(self):
cases = [
(1, 2, 3),
(-1, 1, 0),
(0, 0, 0),
(2, -3, -1),
]
for x, y, expected in cases:
with self.subTest(x…How to Apply the Clean Architecture Dependency Rule in Python
Demonstrates the dependency rule with a Protocol repository, a use case, and a presenter wired together at a composition root.
from dataclasses import dataclass
from typing import List, Protocol
class Repository(Protocol):
def get_items(self) -> List[str]:
...
@dataclass
class InMemoryRepository:
items: List[str]
def get_items(self) -> List[str]:
return self.items
class UseCase:
"""Application layer depends…How to Build a Pipe and Filter Text Processing Chain in Python
A functional pipe-and-filter chain that transforms text through uppercase, whitespace normalization, number removal, stopword filtering, and file export.
import re
import sys
def pipe_filter_chain(stream):
def uppercase(text):
return text.upper()
def strip_whitespace(text):
return " ".join(text.split())
def remove_numbers(text):
return re.sub(r"\d+", "", text)
def remove_stopwords(text, stopwords={"the", "and", "of", "in"}):…How to Mock Service Call Timeouts in Python
Simulate service calls with configurable timeouts using Mock to patch sleep and randomness, covering success and timeout cases.
import time
from unittest.mock import Mock, patch
# Simulate a service call with configurable timeout
def call_service(service_name, timeout=5):
"""Mock a service call that may time out."""
start = time.time()
print(f"Calling {service_name}...")
# Simulate service latency (randomized for realism)…Browse by section
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