human
Complete this python program:
def ensure_dtype(func, argname, arg):
assistant
#Here is the Python program you requested.

    """Argument preprocessor that converts the input into a numpy dtype.
    Examples
    >>> import numpy as np
    >>> from zipline.utils.preprocess import preprocess
    >>> @preprocess(dtype=ensure_dtype)
    ... def foo(dtype):
    ...     return dtype
    >>> foo(float)
    dtype(\float64\)
    """
    try:
        return dtype(arg)
    except TypeError:
        raise TypeError("{func}()    couldn't    convert    argument    {argname}={arg!r}    to    a    numpy    dtype.".format(func=_qualified_name(func), argname=argname, arg=arg))