num_required_args gives unexpected answer on composed methods

using:

• Python 3.6
• toolz 0.9.0

>>> from toolz import compose, num_required_args

>>> int_identity = compose(ord, chr)

>>> req_args = num_required_args(int_identity)

>>> assert req_args == 1, req_args
AssertionError: 0

Note that cytoolz returns a different value on the same test: None. While technically acceptable, I think 1 is the best answer. Our likely workaround for now is:

from toolz.functoolz import Compose, num_required_args

def enhanced_num_required_args(func):
    if isinstance(func, Compose):
        return enhanced_num_required_args(func.first)
    else:
        return num_required_args(func)

Start by reproducing the Python 3.6 example with compose and num_required_args, then read the definitions of Compose and num_required_args mentioned in the issue. Done means the composed int_identity case reports 1, with tests covering the expected behavior and the existing cytoolz distinction considered.