Make service_type a positional argument

This removes the assert to ensure a value for service_type is set. The
keyword style of calling can still be used, so

    microversion_parse.get_version(headers, service_type='compute')

will remain working.

Using an assert for this is probably inadvisable, since it will be
stripped away if python is run with -O.

Change-Id: I9775c5d87890c8ff4a6072c600d54fa47264fa9f

microversion_parse/__init__.py

@@ -19,7 +19,7 @@ import collections
 STANDARD_HEADER = 'openstack-api-version'
 
 
-def get_version(headers, service_type=None, legacy_headers=None):
+def get_version(headers, service_type, legacy_headers=None):
     """Parse a microversion out of headers
 
     :param headers: The headers of a request, dict or list
@@ -46,8 +46,6 @@ def get_version(headers, service_type=None, legacy_headers=None):
     Folded headers are joined by ','.
     """
 
-    assert service_type, 'service type required'
-
     folded_headers = fold_headers(headers)
 
     version = check_standard_header(folded_headers, service_type)

microversion_parse/tests/test_get_version.py

@@ -194,10 +194,6 @@ class TestGetHeaders(testtools.TestCase):
             headers, service_type='compute')
         self.assertEqual(None, version)
 
-        self.assertRaises(AssertionError,
-                          microversion_parse.get_version,
-                          headers)
-
     def test_unfolded_service(self):
         headers = [
             ('header-one', 'alpha'),