Refactor to detect for callability instead of string types, letting the duck type work for string parameters. Fixes #179.

Author: jaraco

setuptools_scm/version.py

@@ -22,13 +22,14 @@ def _warn_if_setuptools_outdated():
 
 def callable_or_entrypoint(group, callable_or_name):
     trace('ep', (group, callable_or_name))
-    if isinstance(callable_or_name, str):
-        for ep in iter_entry_points(group, callable_or_name):
-            trace("ep found:", ep.name)
-            return ep.load()
-    else:
+
+    if callable(callable_or_name):
         return callable_or_name
 
+    for ep in iter_entry_points(group, callable_or_name):
+        trace("ep found:", ep.name)
+        return ep.load()
+
 
 def tag_to_version(tag):
     trace('tag', tag)