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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
How to Convert Data to Strings in Python
Convert common data types like bytes, numbers, containers, and None to readable strings with a safe helper function.
def to_str(value):
"""Convert common types to a readable string, safe for beginners."""
if isinstance(value, bytes):
return value.decode("utf-8")
if isinstance(value, (dict, list, tuple, set)):
return str(value)
if value is None:
return ""
return str(value)
if __name__ == …Find Minimum Value in a List in Python
This code defines a function that finds and returns the minimum value in a list of numbers, handling empty lists gracefully by returning None.
def find_minimum(numbers):
"""
Find and return the minimum value in a list of numbers.
Args:
numbers: List of numeric values
Returns:
The minimum value, or None if the list is empty
"""
if not numbers:
return None
min_value = numbers[0]
for num in n…How to Filter None Values from a Mixed List in Python
Filter None values from a mixed Python list using a list comprehension with the `is not None` condition.
mixed_list = [1, None, "hello", None, 3.14, None, [1, 2], None]
filtered_list = [item for item in mixed_list if item is not None]
print(f"Original list: {mixed_list}")
print(f"Filtered list: {filtered_list}")
print(f"Original length: {len(mixed_list)}, Filtered length: {len(filtered_list)}")How to Find the Maximum Value in a Python List
This code defines a function that finds the largest number in a list by iterating through it, returning None for an empty list, and demonstrates it on a sample list.
def find_max(numbers):
if not numbers:
return None
max_value = numbers[0]
for num in numbers[1:]:
if num > max_value:
max_value = num
return max_value
if __name__ == "__main__":
sample_list = [3, 7, 2, 9, 1, 9]
result = find_max(sample_list)
print(f"Maximum valu…How to Catch KeyError with a Default Value in Python Dictionaries
Safely retrieve dictionary values while catching KeyError and handling None values by returning a default.
def get_value(data, key, default=None):
"""
Safely get a value from a dictionary, returning a default if the key
is missing or the value is None.
"""
try:
value = data[key]
return value if value is not None else default
except KeyError:
return default
if __name__ == "_…How to Handle ValueError with try except in Python
Shows a beginner-friendly try/except pattern that catches ValueError when converting text to an integer, prints a helpful message, and returns None instead of crashing.
def parse_number(text):
try:
return int(text)
except ValueError:
print(f"ValueError: '{text}' is not a valid integer.")
return None
if __name__ == "__main__":
user_input = "abc"
result = parse_number(user_input)
print(f"Parsing '{user_input}' returned: {result}")
vali…How to Use Optional Return in Python Instead of Raising Exceptions
A Python function returns None for missing dictionary keys instead of raising KeyError, enabling graceful lookup handling with type hints.
from typing import Optional
def find_user(users: dict, user_id: int) -> Optional[dict]:
"""
Look up a user by ID. Returns the user dict if found,
otherwise returns None instead of raising KeyError.
"""
return users.get(user_id)
def main() -> None:
users = {
1: {"name": "Alice", "ema…How to check for None and raise helpful errors in Python
A defensive function that explicitly validates data, keys, and values — raising descriptive ValueError and KeyError exceptions before returning a result.
def get_value(data, key):
if data is None:
raise ValueError("data cannot be None")
if key not in data:
raise KeyError(f"key '{key}' not found in data")
result = data[key]
if result is None:
raise ValueError(f"value for key '{key}' is None")
return result
if __name__ == "__…How to handle ZeroDivisionError in Python
Wrap a division operation in try/except to return None or a friendly message instead of crashing when dividing by zero.
def safe_divide(a, b):
"""Return a/b if possible, else None when dividing by zero."""
try:
return a / b
except ZeroDivisionError:
return None
def safe_divide_with_message(a, b):
"""Return a how-to message on divide-by-zero error."""
try:
return a / b
except ZeroDivisio…Try Except ValueError in Python: Handle Conversion Errors
Catch ValueError exceptions when converting strings to integers or performing arithmetic, returning None on failure instead of crashing.
def convert_to_int(value):
try:
return int(value)
except ValueError as error:
print(f"Conversion failed: {error}")
print(f"Problem value was: {repr(value)}")
return None
def divide_numbers(numerator, denominator):
try:
result = numerator / denominator
retur…How to Recursively Remove None Values from Nested Dictionaries in Python
Recursively removes all None values from nested dictionaries and lists while preserving non-None data.
def prune_none(obj):
if isinstance(obj, dict):
return {
k: prune_none(v)
for k, v in obj.items()
if v is not None and prune_none(v) is not None
}
elif isinstance(obj, list):
pruned = [prune_none(item) for item in obj]
pruned = [item for item i…Parse Env Vars into Typed Dict in Python
Convert a list of environment variable names into a dictionary with automatically detected types (bool, int, float, or string), defaulting missing vars to None.
import os
from typing import Any, Dict
def parse_env_vars(env_names: list[str], env: Dict[str, str] | None = None) -> Dict[str, Any]:
"""Parse a list of environment variable names into a typed dict.
Each variable is parsed as:
- bool: "true"/"false" (case-insensitive)
- int: if it can be converted t…Find the First Index Where a Condition Is True in Python
Search any iterable for the first element matching a predicate and return its index, or -1 if none match.
def first_true_index(items, condition):
"""Return the first index where condition(item) is True, or -1 if none match."""
for i, item in enumerate(items):
if condition(item):
return i
return -1
if __name__ == "__main__":
numbers = [1, 3, 5, 8, 10, 12]
# Find first number greate…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 Find the Previous Smaller Element in Python
Use a monotonic stack to find the nearest smaller element to the left of each item in a list, returning -1 when none exists.
from collections import deque
def previous_smaller_elements(arr):
stack = deque()
result = [-1] * len(arr)
for i in range(len(arr)):
while stack and arr[stack[-1]] >= arr[i]:
stack.pop()
if stack:
result[i] = arr[stack[-1]]
stack.append(i)
return resul…Normalize Data in Python with Comprehensions and Generators
Clean a list by dropping None values with a comprehension, then min-max normalize it using a lazy generator expression — a beginner-friendly data preparation pattern.
import statistics
# Sample raw data including missing and outlier-ish values
raw = [22, 18, None, 25, 30, 19, 22, 17, None, 28, 24]
# Clean the data: drop None values using a list comprehension
clean = [x for x in raw if x is not None]
# Normalize using min-max scaling with a generator expression
min_val = min(clea…Filter Records by Required Fields in Python
Filter a list of dictionaries, keeping only records where every required field is present and not None.
def filter_records(records, required_fields):
"""Return only records that have all required fields non-null."""
return [
record for record in records
if all(record.get(field) is not None for field in required_fields)
]
if __name__ == "__main__":
sample_records = [
{"name": "Al…Trigger a Pipeline When a New File Appears in a Directory
Poll a directory every 0.5 seconds and return the name of the first new file that appears, or None after a timeout.
import time
from pathlib import Path
def watch_for_file(directory: str, interval: float = 0.5, timeout: float = 10.0) -> str | None:
"""Poll a directory and trigger when a new file appears."""
watch_dir = Path(directory)
watch_dir.mkdir(exist_ok=True)
known_files = set(watch_dir.iterdir())
s…How to Auto-Suggest a SemVer Bump From Git Commit Messages in Python
This code scans Git commit messages (recent or sample) and suggests the next Semantic Versioning bump type — major, minor, patch, or none.
import re
import subprocess
from pathlib import Path
def get_commit_messages(path="."):
"""Read commit messages from a repo or use sample messages."""
if (Path(path) / ".git").exists():
out = subprocess.run(
["git", "-C", path, "log", "--pretty=%s"], capture_output=True, text=True
…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))How to Mock HTTP 304 Responses with If-None-Match in Python
Spin up a local HTTP server that returns a 304 Not Modified when a request carries a matching ETag, useful for testing cache behavior.
from http.server import BaseHTTPRequestHandler, HTTPServer
from threading import Thread
import urllib.request
ETAG = '"abc123"'
BODY = b'{"status": "ok"}'
class MockServer(BaseHTTPRequestHandler):
def do_GET(self):
if self.headers.get('If-None-Match') == ETAG:
self.send_response(304)
…How to Impute Missing Values with Mean in Python
Replace None values in a list with the mean of the existing values using Python's statistics module.
import statistics
from statistics import mean
def impute_mean(values):
"""Replace None with the mean of the non-None values."""
# Filter out None to compute the mean of existing values
valid = [v for v in values if v is not None]
if not valid:
return values # nothing to impute if all are Non…Browse by section
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