From 974a0d47550cb0a96f1b98daba39868b03a15bc3 Mon Sep 17 00:00:00 2001
From: Guido van Rossum <guido@python.org>
Date: Tue, 4 Oct 2016 16:42:58 -0700
Subject: [PATCH 1/2] Add a (somewhat simple-minded) cache to the Python 2
 version too.

---
 python2/typing.py | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/python2/typing.py b/python2/typing.py
index f6a73d706..8a1d18ee4 100644
--- a/python2/typing.py
+++ b/python2/typing.py
@@ -563,6 +563,28 @@ def __subclasscheck__(self, cls):
 AnyStr = TypeVar('AnyStr', bytes, unicode)
 
 
+def _tp_cache(func, maxsize=128):
+    cache = {}
+
+    @functools.wraps(func)
+    def inner(*args):
+        key = args
+        try:
+            return cache[key]
+        except TypeError:
+            # Assume it's an unhashable argument.
+            return func(*args)
+        except KeyError:
+            value = func(*args)
+            if len(cache) >= maxsize:
+                # If the cache grows too much, just start over.
+                cache.clear()
+            cache[key] = value
+            return value
+
+    return inner
+
+
 class UnionMeta(TypingMeta):
     """Metaclass for Union."""
 
@@ -686,6 +708,7 @@ def __repr__(self):
                                      for t in self.__union_params__))
         return r
 
+    @_tp_cache
     def __getitem__(self, parameters):
         if self.__union_params__ is not None:
             raise TypeError(
@@ -731,6 +754,7 @@ class _Optional(_FinalTypingBase):
     __metaclass__ = OptionalMeta
     __slots__ = ()
 
+    @_tp_cache
     def __getitem__(self, arg):
         arg = _type_check(arg, "Optional[t] requires a single type.")
         return Union[arg, type(None)]
@@ -791,6 +815,7 @@ def __repr__(self):
                 ', '.join(params))
         return r
 
+    @_tp_cache
     def __getitem__(self, parameters):
         if self.__tuple_params__ is not None:
             raise TypeError("Cannot re-parameterize %r" % (self,))
@@ -1109,6 +1134,7 @@ def __eq__(self, other):
     def __hash__(self):
         return hash((self.__name__, self.__parameters__))
 
+    @_tp_cache
     def __getitem__(self, params):
         if not isinstance(params, tuple):
             params = (params,)

From 658671e7801aae365c5491a47c318340de021391 Mon Sep 17 00:00:00 2001
From: Guido van Rossum <guido@python.org>
Date: Wed, 5 Oct 2016 08:16:34 -0700
Subject: [PATCH 2/2] Make maxsize a local (it's useless as an arg anyway)

---
 python2/typing.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/python2/typing.py b/python2/typing.py
index 8a1d18ee4..6cd51c6b7 100644
--- a/python2/typing.py
+++ b/python2/typing.py
@@ -563,7 +563,8 @@ def __subclasscheck__(self, cls):
 AnyStr = TypeVar('AnyStr', bytes, unicode)
 
 
-def _tp_cache(func, maxsize=128):
+def _tp_cache(func):
+    maxsize = 128
     cache = {}
 
     @functools.wraps(func)