The discovery.build_from_document function assumes that service is of type str, however when running in Python3 instead of str it can be of type bytes.

Because of this wrong assumption, the function fails on line 337 where the bytes string is compared to an actual text string.

The google-api-python-client version where i've seen this problem is 1.7.7

Solution

Add a check, if service is a bytes string convert it using UTF-8 format

  if isinstance(service, six.string_types):
      service = json.loads(service)
+ elif isinstance(service, six.binary_type):
+  service = json.loads(service.decode('utf8'))

This fixes my problem (observed when using this library in Google3)