Implement get_file

pip/commands/configuration.py

@@ -180,6 +180,11 @@ class ConfigurationCommand(Command):
             return ERROR
 
         file = self.configuration.get_file()
+        if file is None:
+            logger.error(
+                "Could not determine appropriate file."
+            )
+            return ERROR
 
         try:
             subprocess.check_call([options.editor, file])

pip/configuration.py

@@ -89,6 +89,14 @@ class Configuration(object):
         if not self.isolated:
             self._load_environment_vars()
 
+    def get_file(self):
+        """Returns the file with highest priority in configuration
+        """
+        try:
+            return self._get_parser_to_modify()[0]
+        except IndexError:
+            return None
+
     def items(self):
         """Returns key-value pairs like dict.items() representing the loaded
         configuration