MAINT: Add python 3.6 support to suppress_warnings

Python 3.6 has two methods for showing warnings, so we have to support
both ways (strictly speaking, on python 3.6 itself only the new would
probably be needed).

Also adds the _filters_mutated() call to replace manual registry
clearing. This is basically the fix that newer python versions have
to avoid the issue making the manual clearing unnecessary.

Closes gh-8176

1 files changed, 26 insertions, 3 deletions

diff --git a/numpy/testing/utils.py b/numpy/testing/utils.py
index b01de173d..d17e7e404 100644
--- a/numpy/testing/utils.py
+++ b/numpy/testing/utils.py
@@ -2027,6 +2027,11 @@ class suppress_warnings(object):
         self._forwarding_rule = forwarding_rule
 
     def _clear_registries(self):
+        if hasattr(warnings, "_filters_mutated"):
+            # clearing the registry should not be necessary on new pythons,
+            # instead the filters should be mutated.
+            warnings._filters_mutated()
+            return
         # Simply clear the registry, this should normally be harmless,
         # note that on new pythons it would be invalidated anyway.
         for module in self._tmp_modules:
@@ -2116,6 +2121,8 @@ class suppress_warnings(object):
             raise RuntimeError("cannot enter suppress_warnings twice.")
 
         self._orig_show = warnings.showwarning
+        if hasattr(warnings, "_showwarnmsg"):
+            self._orig_showmsg = warnings._showwarnmsg
         self._filters = warnings.filters
         warnings.filters = self._filters[:]
 
@@ -2139,20 +2146,29 @@ class suppress_warnings(object):
                     module=module_regex)
                 self._tmp_modules.add(mod)
         warnings.showwarning = self._showwarning
+        if hasattr(warnings, "_showwarnmsg"):
+            warnings._showwarnmsg = self._showwarnmsg
         self._clear_registries()
 
         return self
 
     def __exit__(self, *exc_info):
         warnings.showwarning = self._orig_show
+        if hasattr(warnings, "_showwarnmsg"):
+            warnings._showwarnmsg = self._orig_showmsg
         warnings.filters = self._filters
         self._clear_registries()
         self._entered = False
         del self._orig_show
         del self._filters
 
+    def _showwarnmsg(self, msg):
+        self._showwarning(msg.message, msg.category, msg.filename, msg.lineno,
+                          msg.file, msg.line, use_warnmsg=msg)
+
     def _showwarning(self, message, category, filename, lineno,
                      *args, **kwargs):
+        use_warnmsg = kwargs.pop("use_warnmsg", None)
         for cat, _, pattern, mod, rec in (
                 self._suppressions + self._tmp_suppressions)[::-1]:
             if (issubclass(category, cat) and
@@ -2179,8 +2195,11 @@ class suppress_warnings(object):
         # There is no filter in place, so pass to the outside handler
         # unless we should only pass it once
         if self._forwarding_rule == "always":
-            self._orig_show(message, category, filename, lineno,
-                            *args, **kwargs)
+            if use_warnmsg is None:
+                self._orig_show(message, category, filename, lineno,
+                                *args, **kwargs)
+            else:
+                self._orig_showmsg(use_warnmsg)
             return
 
         if self._forwarding_rule == "once":
@@ -2193,7 +2212,11 @@ class suppress_warnings(object):
         if signature in self._forwarded:
             return
         self._forwarded.add(signature)
-        self._orig_show(message, category, filename, lineno, *args, **kwargs)
+        if use_warnmsg is None:
+            self._orig_show(message, category, filename, lineno, *args,
+                            **kwargs)
+        else:
+            self._orig_showmsg(use_warnmsg)
 
     def __call__(self, func):
         """