Like find, but raises ValueError when the substring is not found.
Calls str.index element-wise.
a : array_like of str or unicode
sub : str or unicode
start, end : int, optional
out : ndarray
Output array of ints. Returns -1 if sub is not found.
See also
find, str.find
numpy.core.defchararray.find
numpy.core.defchararray.isalpha
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