def first_element(obj):
if isinstance(obj, Iterator):<EOL><INDENT>raise RuntimeError(<EOL>"<STR_LIT>")<EOL><DEDENT>return next(iter(obj))<EOL>
Return the first element of `obj`

Parameters
----------
obj : iterable
    Should not be an iterator

Returns
-------
out : object
    First element of `obj`. Raise a class:`StopIteration`
    exception if `obj` is empty.