Add rjiang suggestion for counting setup.py files

src/python/pants/backend/python/targets/python_distribution.py

@@ -54,12 +54,12 @@ def __init__(self,
     super(PythonDistribution, self).__init__(address=address, payload=payload, **kwargs)
     self.add_labels('python')
 
-    sources_basenames = [os.path.basename(source) for source in sources]
-    if not 'setup.py' in sources_basenames:
+    count_of_setup_py = [os.path.basename(s) for s in sources].count('setup.py')
+    if count_of_setup_py == 0:
       raise TargetDefinitionException(self,
         'A setup.py is required to create a python_dist. '
         'You must include a setup.py file in your sources field.')
-    if len(filter(lambda x: x == 'setup.py', sources_basenames)) > 1:
+    if count_of_setup_py > 1:
       raise TargetDefinitionException(self,
         'Multiple setup.py files detected. You can only specify one '
         'setup.py in a python_dist target.')