On Python 3.7.0a4 and later (including 3.7.0b4), find_library currently always returns None on macOS. It works on 3.7.0a3 and earlier. Tested on macOS 10.11 and 10.13.

Expected result: Tested on 3.6.5, 3.7.0a1 and 3.7.0a3:

>>> from ctypes.util import find_library
>>> find_library('iconv')
'/usr/lib/libiconv.dylib'
>>> find_library('c')
'/usr/lib/libc.dylib'
>>>

Current output on 3.7.0a4 to 3.7.0b3:

>>> from ctypes.util import find_library
>>> find_library('iconv')
>>> find_library('c')
>>>