Conditionals and Truthiness

Truthiness

Empty containers, 0, and None are falsy. This can be useful, but it can also hide bugs.

Guard Clauses

def process(user: dict) -> str:
    if not user:
        raise ValueError("user required")

    user_id = user.get("id")
    if user_id is None:
        raise ValueError("user.id required")

    return f"ok:{user_id}"

Beware of or-default

timeout = config.get("timeout") or 10  # BUG if timeout can be 0

If 0 is a valid value, use an explicit is None check instead.

Operational Checklist

• Decide whether 0/""/empty containers are valid values.
• Use explicit is None checks where it matters.
• Avoid deeply nested conditionals; split logic into small functions.

Failure Modes

• Falsy bug: valid values drop into defaults unexpectedly.
• Complex logic: multi-and/or conditions become untestable.