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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
Create a retry decorator with max attempts in Python
A decorator that retries a function up to a specified number of times when it raises an exception, with an optional delay between attempts.
import functools
import time
def retry(max_attempts, delay=0.1):
"""Retry a function up to max_attempts times on exception."""
def decorator(func):
@functools.wraps(func)
def wrapper(*args, **kwargs):
for attempt in range(1, max_attempts + 1):
try:
…Catch RecursionError and Fail Gracefully in Python
Wrap a recursive function call in a try-except block to catch RecursionError and print a graceful failure message instead of crashing.
def compute_factorial_recursive(n):
"""Compute factorial recursively, raising RecursionError for deep recursion."""
if n == 0:
return 1
return n * compute_factorial_recursive(n - 1)
if __name__ == "__main__":
try:
result = compute_factorial_recursive(10000)
print(f"Factorial c…Catch ValueError and print friendly message in Python
Wrap an int() call in a try/except block and print a friendly message when ValueError is raised.
try:
number = int("not_a_number")
except ValueError:
print("That's not a valid number. Please enter digits only.")Collect Multiple Validation Errors in Python Before Raising
A chainable Validator class that accumulates all validation errors and raises them together in a single exception.
class ValidationError(Exception):
pass
class Validator:
def __init__(self):
self.errors = []
def validate_required(self, value, field_name):
if not value:
self.errors.append(f"{field_name} is required")
return self
def validate_email(self, email):
…Handle ValueError and ZeroDivisionError in Python with try except
Learn how to catch ValueError and ZeroDivisionError in Python with a practical safe_divide function and demonstrate error handling for invalid conversions.
def safe_divide(numerator, denominator):
try:
result = numerator / denominator
except ValueError as e:
print(f"ValueError caught: {e}")
return None
except ZeroDivisionError:
print("Cannot divide by zero!")
return None
return result
# Test cases
print(safe_divide…How to Assert Preconditions with Descriptive Messages in Python
Use Python's assert statement with a custom message to validate function preconditions and fail fast with clear diagnostics.
def divide(dividend, divisor):
assert divisor != 0, f"Divisor must be non-zero, got {divisor!r}"
return dividend / divisor
if __name__ == "__main__":
print(divide(10, 2))
try:
divide(10, 0)
except AssertionError as e:
print(f"AssertionError: {e}")How to Catch ValueError in Python
Shows how to handle a ValueError with try-except so a bad int() conversion doesn't crash the script.
try:
number = int("not_a_number")
print(f"Parsed successfully: {number}")
except ValueError as e:
print(f"Error: {e}")
print("Please provide a valid integer.")
print("Program continues running.")How to Catch ValueError in Python (try except)
Handle invalid numeric input by catching ValueError in a try/except block and returning a friendly error message.
def parse_number(text):
try:
number = int(text)
return f"Parsed number: {number}"
except ValueError as error:
return f"Error: '{text}' is not a valid number ({error})"
if __name__ == "__main__":
examples = ["42", "hello", "3.14", "100"]
for item in examples:
print(pars…How to Handle ValueError Exceptions in Python
A beginner-friendly example showing how to catch ValueError and related exceptions with try-except blocks in Python.
def divide_numbers(a, b):
try:
result = a / b
return f"{a} / {b} = {result}"
except ZeroDivisionError:
return "Error: Cannot divide by zero."
except TypeError:
return "Error: Please provide numbers, not strings."
except ValueError:
return "Error: Invalid value de…How to Handle ValueError When Converting Strings to Integers in Python
Convert text to an integer with a try-except block that catches ValueError and prints beginner-friendly error messages.
def parse_number(text):
"""Convert text to an integer, showing beginner-friendly error handling."""
try:
number = int(text)
print(f"Successfully parsed: {number}")
return number
except ValueError as e:
print(f"Error: '{text}' is not a valid number.")
print(f"Debuggin…How to Handle ValueError and Multiple Exceptions in Python
This code demonstrates try/except blocks for beginners, handling ZeroDivisionError, TypeError, and ValueError with two practical functions: dividing numbers and parsing strings to floats.
def divide_numbers(a, b):
"""Divide two numbers with error handling for beginners."""
try:
result = a / b
print(f"{a} / {b} = {result}")
return result
except ZeroDivisionError:
print(f"Error: Cannot divide {a} by zero!")
except TypeError:
print(f"Error: Both argu…How to Handle ValueError in Python (try except)
Learn to catch ValueError and other exceptions with try-except blocks in Python using practical division and string-to-float conversion examples.
def divide_numbers(a, b):
"""Divide two numbers and handle ValueError safely."""
try:
result = a / b
return f"{a} / {b} = {result}"
except ZeroDivisionError:
return "Error: Cannot divide by zero!"
except TypeError:
return "Error: Both inputs must be numbers!"
def parse…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 Handle ValueError with try-except in Python
Build a beginner-friendly division calculator that catches ValueError and ZeroDivisionError with try-except blocks.
def get_number(prompt="Enter a number: "):
while True:
try:
value = float(input(prompt))
return value
except ValueError:
print("That's not a valid number. Please try again.")
def divide_numbers(a, b):
try:
result = a / b
return result
ex…How to Inspect Local Variables in an except Block in Python
Capture and print local variables at the moment an exception occurs using locals() inside an except block.
def risky_operation(value):
try:
result = 10 / value
return result
except ZeroDivisionError as e:
local_vars = dict(locals())
print(f"Error: {e}")
print("Local variables at exception:")
for key, val in local_vars.items():
print(f" {key} = {val}")
…How to Log Exceptions with traceback.format_exc in Python
Capture and log a full traceback string when an exception occurs using Python's traceback.format_exc() and logging module.
import traceback
import logging
def risky_operation(value):
return 10 / value
logging.basicConfig(level=logging.ERROR, format='%(asctime)s - %(levelname)s - %(message)s')
def main():
try:
result = risky_operation(0)
print(f"Result: {result}")
except ZeroDivisionError:
error_msg =…How to Print an Exception Chain in Python for Debugging
A helper that walks an exception's __cause__ and __context__ chain, printing each level with indentation to make debugging nested errors clearer.
import sys
import traceback
def pretty_exception_chain(exc):
"""Print the full exception chain with cause/context details."""
chain = []
current = exc
seen = set()
while current is not None and id(current) not in seen:
seen.add(id(current))
chain.append(current)
curren…How to Raise a Custom Exception with Extra Context in Python
Define a custom exception that carries extra context fields and raise it to provide richer error information.
class InsufficientFundsError(Exception):
def __init__(self, balance, amount):
self.balance = balance
self.amount = amount
super().__init__(f"Withdrawal of ${amount} failed: balance ${balance} is insufficient")
def withdraw(balance, amount):
if amount > balance:
raise Insuffici…How to Re-raise Exceptions with 'raise from' in Python
Shows how to re-raise an exception with explicit context chaining using the 'raise ... from ...' syntax, so the original cause is preserved for debugging.
def divide_with_chain(a, b):
try:
result = a / b
return result
except ZeroDivisionError as original_error:
# Re-raise with explicit chaining context
raise ValueError("Cannot divide by zero") from original_error
def explain_chain():
try:
divide_with_chain(10, 0)
…How to Serialize an Exception to a JSON-Safe Dict in Python
Convert any Python exception into a JSON-safe dictionary with type, message, and the last few traceback lines for logging.
import json
import traceback
from typing import Any
def exception_to_dict(exc: Exception) -> dict[str, Any]:
"""Convert an exception into a JSON-safe dictionary."""
return {
"type": type(exc).__name__,
"message": str(exc),
"traceback": traceback.format_exc().strip().split("\n")[-3:],
…How to Simulate Timeout with Custom TimeoutError in Python
Run a function in a daemon thread and raise a custom TimeoutError if it exceeds a specified time limit.
import time
from typing import Callable, TypeVar
T = TypeVar("T")
class TimeoutError(Exception):
"""Raised when an operation exceeds its time limit."""
def __init__(self, message: str = "Operation timed out"):
self.message = message
super().__init__(self.message)
def run_with_timeout(func…How to Test Exceptions in Python with pytest.raises
Learn the pytest.raises pattern to assert that specific exceptions are raised and validate their messages.
import pytest
def divide(a: int, b: int) -> float:
if b == 0:
raise ValueError("Cannot divide by zero")
return a / b
def test_divide_by_zero_raises():
with pytest.raises(ValueError, match="Cannot divide by zero"):
divide(10, 0)
def test_divide_by_zero_raises_exact_match():
with py…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 Use a Fallback Path with FileNotFoundError in Python
Read a primary file and fall back to a backup file when the first is missing, returning an empty string if both fail.
import pathlib
def read_config(path):
primary = pathlib.Path(path)
fallback = pathlib.Path("config_backup.json")
try:
with primary.open("r") as f:
return f.read()
except FileNotFoundError:
try:
with fallback.open("r") as f:
return f.read()
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Copy-ready Python snippets for learners and developers
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- Pick a topic section — strings, lists, files, functions, and more
- Open a sample, read How it works, and copy the code block
- Run it in the IDE, tweak values, then take a related quiz or tutorial lesson
Samples vs tutorials and challenges
Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.