input_validation.py 文件源码

def expect_element(*_pos, **named):
    """
    Preprocessing decorator that verifies inputs are elements of some
    expected collection.

    Usage
    -----
    >>> @expect_element(x=('a', 'b'))
    ... def foo(x):
    ...    return x.upper()
    ...
    >>> foo('a')
    'A'
    >>> foo('b')
    'B'
    >>> foo('c')
    Traceback (most recent call last):
       ...
    ValueError: foo() expected a value in ('a', 'b') for argument 'x', but got 'c' instead.  # noqa

    Notes
    -----
    This uses the `in` operator (__contains__) to make the containment check.
    This allows us to use any custom container as long as the object supports
    the container protocol.
    """
    if _pos:
        raise TypeError("expect_element() only takes keyword arguments.")

    def _expect_element(collection):
        template = (
            "%(funcname)s() expected a value in {collection} "
            "for argument '%(argname)s', but got %(actual)s instead."
        ).format(collection=collection)
        return make_check(
            ValueError,
            template,
            complement(op.contains(collection)),
            repr,
        )
    return preprocess(**valmap(_expect_element, named))