Use dict instead of OrderedDict on Python 3.7

OrderedDict is quite a bit heavier than just a dict.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/_pytest/compat.py b/src/_pytest/compat.py
index ba225eb8f..6a0614f01 100644
--- a/src/_pytest/compat.py
+++ b/src/_pytest/compat.py
@@ -381,3 +381,15 @@ else:
                 return self
             value = instance.__dict__[self.func.__name__] = self.func(instance)
             return value
+
+
+# Sometimes an algorithm needs a dict which yields items in the order in which
+# they were inserted when iterated. Since Python 3.7, `dict` preserves
+# insertion order. Since `dict` is faster and uses less memory than
+# `OrderedDict`, prefer to use it if possible.
+if sys.version_info >= (3, 7):
+    order_preserving_dict = dict
+else:
+    from collections import OrderedDict
+
+    order_preserving_dict = OrderedDict