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Errors & debugging

Handle failures gracefully, raise helpful errors, and debug with confidence.

4 matches

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__ == "_…

13 0 Open

Errors & debugging easy

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.

optional typing dict-get

Python

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…

14 0 Open

Errors & debugging easy

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.

none error-handling validation

Python

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__ == "__…

15 0 Open

Errors & debugging easy

Python dict try-except KeyError EAFP vs LBYL

Compare EAFP (try-except) and LBYL (if-in-check) styles for safely accessing dictionary keys, with working examples in Python.

eafp lbyl dictionary

Python

def safe_get_lbyl(d, key):
    if key in d:
        return d[key]
    return "default-lbyl"

def safe_get_eafp(d, key):
    try:
        return d[key]
    except KeyError:
        return "default-eafp"

if __name__ == "__main__":
    data = {"name": "Alice", "age": 30}
    print("LBYL:", safe_get_lbyl(data, "missing")…

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