Merge pull request #4227 from blueyed/_getconftest_pathlist-lru

Use functools.lru_cache with _getconftest_pathlist

src/_pytest/config/__init__.py

@@ -1,6 +1,7 @@
 """ command line options, ini-file and conftest.py processing. """
 from __future__ import absolute_import, division, print_function
 import argparse
+import functools
 import inspect
 import shlex
 import types
@@ -907,6 +908,10 @@ class Config(object):
             values.append(relroot)
         return values
 
+    if six.PY3:
+        # once we drop Python 2, please change this to use the normal decorator syntax (#4227)
+        _getconftest_pathlist = functools.lru_cache(maxsize=None)(_getconftest_pathlist)
+
     def _get_override_ini_value(self, name):
         value = None
         # override_ini is a list of "ini=value" options