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Reference library

Errors & debugging

Handle failures gracefully and write clearer error messages for future you.

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Errors & debugging medium

Raise a clear custom error

Validate input early and raise ValueError with a helpful message.

errors raise validation
Python 
def positive_only(n):
    """Return n if it is strictly positive."""
    if n <= 0:
        raise ValueError(f"Expected a positive number, got {n}")
    return n


print(positive_only(5))
try:
    positive_only(-1)
except ValueError as exc:
    print(exc)
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Errors & debugging — Python code examples

What you will find here

This page collects errors & debugging snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.

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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.

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