python-mastery/Exercises/soln7_1.md

Exercise 7.1 - Solution

# validate.py
...

from inspect import signature

def validated(func):
    sig = signature(func)

    # Gather the function annotations
    annotations = dict(func.__annotations__)

    # Get the return annotation (if any)
    retcheck = annotations.pop('return', None)

    def wrapper(*args, **kwargs):
        bound = sig.bind(*args, **kwargs)
        errors = []

        # Enforce argument checks
        for name, validator in annotations.items():
            try:
                validator.check(bound.arguments[name])
            except Exception as e:
                errors.append(f'    {name}: {e}')

        if errors:
            raise TypeError('Bad Arguments\n' + '\n'.join(errors))

        result = func(*args, **kwargs)

        # Enforce return check (if any)
        if retcheck:
            try:
                retcheck.check(result)
            except Exception as e:
                raise TypeError(f'Bad return: {e}') from None
        return result

    return wrapper

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