[WIP] bpo-27535: Optimize warnings

Lib/test/test_warnings/__init__.py

@@ -125,6 +125,8 @@ def test_ignore(self):
             self.module.filterwarnings("ignore", category=UserWarning)
             self.module.warn("FilterTests.test_ignore", UserWarning)
             self.assertEqual(len(w), 0)
+            self.assertEqual(list(__warningregistry__.keys()),
+                             ['version'])
 
     def test_ignore_after_default(self):
         with original_warnings.catch_warnings(record=True,
@@ -705,6 +707,7 @@ def test_default_action(self):
                 self.module.defaultaction = "ignore"
                 __warningregistry__ = {}
                 registry = {}
+                self.module._filters_mutated()
                 self.module.warn_explicit(message, UserWarning, "<test>", 44,
                                             registry=registry)
                 self.assertEqual(len(w), 0)
@@ -847,13 +850,14 @@ def test_issue31416(self):
         # bad warnings.filters or warnings.defaultaction.
         wmod = self.module
         with original_warnings.catch_warnings(module=wmod):
-            wmod.filters = [(None, None, Warning, None, 0)]
             with self.assertRaises(TypeError):
+                wmod._add_filter(None, None, Warning, None, 0)
                 wmod.warn_explicit('foo', Warning, 'bar', 1)
 
-            wmod.filters = []
+        with original_warnings.catch_warnings(module=wmod):
             with support.swap_attr(wmod, 'defaultaction', None), \
                  self.assertRaises(TypeError):
+                wmod.resetwarnings()
                 wmod.warn_explicit('foo', Warning, 'bar', 1)
 
     @support.cpython_only
@@ -1011,14 +1015,14 @@ def test_catch_warnings_defaults(self):
         with wmod.catch_warnings(module=wmod) as w:
             self.assertIsNone(w)
             self.assertIs(wmod.showwarning, orig_showwarning)
-            self.assertIsNot(wmod.filters, orig_filters)
+            self.assertIs(wmod.filters, orig_filters)
         self.assertIs(wmod.filters, orig_filters)
         if wmod is sys.modules['warnings']:
             # Ensure the default module is this one
             with wmod.catch_warnings() as w:
                 self.assertIsNone(w)
                 self.assertIs(wmod.showwarning, orig_showwarning)
-                self.assertIsNot(wmod.filters, orig_filters)
+                self.assertIs(wmod.filters, orig_filters)
             self.assertIs(wmod.filters, orig_filters)
 
     def test_record_override_showwarning_before(self):

Lib/warnings.py

@@ -137,8 +137,16 @@ def filterwarnings(action, message="", category=Warning, module="", lineno=0,
     assert isinstance(module, str), "module must be a string"
     assert isinstance(lineno, int) and lineno >= 0, \
            "lineno must be an int >= 0"
-    _add_filter(action, re.compile(message, re.I), category,
-            re.compile(module), lineno, append=append)
+
+    if message:
+        regex = re.compile(message, re.I)
+    else:
+        regex = None
+    if module:
+        module = re.compile(module)
+    else:
+        module = None
+    _add_filter(action, regex, category, module, lineno, append=append)
 
 def simplefilter(action, category=Warning, lineno=0, append=False):
     """Insert a simple entry into the list of warnings filters (at the front).
@@ -157,22 +165,26 @@ def simplefilter(action, category=Warning, lineno=0, append=False):
     _add_filter(action, None, category, None, lineno, append=append)
 
 def _add_filter(*item, append):
+    global filters
     # Remove possible duplicate filters, so new one will be placed
     # in correct place. If append=True and duplicate exists, do nothing.
+    filters_list = list(filters)
     if not append:
         try:
-            filters.remove(item)
+            filters_list.remove(item)
         except ValueError:
             pass
-        filters.insert(0, item)
+        filters_list.insert(0, item)
     else:
-        if item not in filters:
-            filters.append(item)
+        if item not in filters_list:
+            filters_list.append(item)
+    filters = tuple(filters_list)
     _filters_mutated()
 
 def resetwarnings():
     """Clear the list of warning filters, so that no filters are active."""
-    filters[:] = []
+    global filters
+    filters = ()
     _filters_mutated()
 
 class _OptionError(Exception):
@@ -353,7 +365,6 @@ def warn_explicit(message, category, filename, lineno,
         action = defaultaction
     # Early exit actions
     if action == "ignore":
-        registry[key] = 1
         return
 
     # Prime the linecache for formatting, in case the
@@ -455,7 +466,7 @@ def __enter__(self):
             raise RuntimeError("Cannot enter %r twice" % self)
         self._entered = True
         self._filters = self._module.filters
-        self._module.filters = self._filters[:]
+        self._module.filters = tuple(self._filters)
         self._module._filters_mutated()
         self._showwarning = self._module.showwarning
         self._showwarnmsg_impl = self._module._showwarnmsg_impl
@@ -492,8 +503,9 @@ def __exit__(self, *exc_info):
     defaultaction = _defaultaction
     onceregistry = _onceregistry
     _warnings_defaults = True
+    filters = tuple(filters)
 except ImportError:
-    filters = []
+    filters = ()
     defaultaction = "default"
     onceregistry = {}
 

Misc/NEWS.d/next/Library/2017-11-21-16-05-35.bpo-27535.JLhcNz.rst

@@ -0,0 +1,4 @@
+The warnings module doesn't leak memory anymore in the hidden warnings
+registry for the "ignore" action of warnings filters. warn_explicit()
+function doesn't add the warning key to the registry anymore for the
+"ignore" action.