1 files changed, 54 insertions, 19 deletions

diff --git a/Lib/warnings.py b/Lib/warnings.py
index 70d087e6d9..c6631fcbf4 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -21,9 +21,15 @@ def showwarning(message, category, filename, lineno, file=None, line=None):
 
 def formatwarning(message, category, filename, lineno, line=None):
     """Function to format a warning the standard way."""
-    import linecache
     s =  "%s:%s: %s: %s\n" % (filename, lineno, category.__name__, message)
-    line = linecache.getline(filename, lineno) if line is None else line
+    if line is None:
+        try:
+            import linecache
+            line = linecache.getline(filename, lineno)
+        except Exception:
+            # When a warning is logged during Python shutdown, linecache
+            # and the import machinery don't work anymore
+            line = None
     if line:
         line = line.strip()
         s += "  %s\n" % line
@@ -50,13 +56,8 @@ 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"
-    item = (action, re.compile(message, re.I), category,
-            re.compile(module), lineno)
-    if append:
-        filters.append(item)
-    else:
-        filters.insert(0, item)
-    _filters_mutated()
+    _add_filter(action, re.compile(message, re.I), category,
+            re.compile(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).
@@ -72,11 +73,20 @@ def simplefilter(action, category=Warning, lineno=0, append=False):
                       "once"), "invalid action: %r" % (action,)
     assert isinstance(lineno, int) and lineno >= 0, \
            "lineno must be an int >= 0"
-    item = (action, None, category, None, lineno)
-    if append:
-        filters.append(item)
-    else:
+    _add_filter(action, None, category, None, lineno, append=append)
+
+def _add_filter(*item, append):
+    # Remove possible duplicate filters, so new one will be placed
+    # in correct place. If append=True and duplicate exists, do nothing.
+    if not append:
+        try:
+            filters.remove(item)
+        except ValueError:
+            pass
         filters.insert(0, item)
+    else:
+        if item not in filters:
+            filters.append(item)
     _filters_mutated()
 
 def resetwarnings():
@@ -160,6 +170,20 @@ def _getcategory(category):
     return cat
 
 
+def _is_internal_frame(frame):
+    """Signal whether the frame is an internal CPython implementation detail."""
+    filename = frame.f_code.co_filename
+    return 'importlib' in filename and '_bootstrap' in filename
+
+
+def _next_external_frame(frame):
+    """Find the next frame that doesn't involve CPython internals."""
+    frame = frame.f_back
+    while frame is not None and _is_internal_frame(frame):
+        frame = frame.f_back
+    return frame
+
+
 # Code typically replaced by _warnings
 def warn(message, category=None, stacklevel=1):
     """Issue a warning, or maybe ignore it or raise an exception."""
@@ -169,16 +193,28 @@ def warn(message, category=None, stacklevel=1):
     # Check category argument
     if category is None:
         category = UserWarning
-    assert issubclass(category, Warning)
+    if not (isinstance(category, type) and issubclass(category, Warning)):
+        raise TypeError("category must be a Warning subclass, "
+                        "not '{:s}'".format(type(category).__name__))
     # Get context information
     try:
-        caller = sys._getframe(stacklevel)
+        if stacklevel <= 1 or _is_internal_frame(sys._getframe(1)):
+            # If frame is too small to care or if the warning originated in
+            # internal code, then do not try to hide any frames.
+            frame = sys._getframe(stacklevel)
+        else:
+            frame = sys._getframe(1)
+            # Look for one frame less since the above line starts us off.
+            for x in range(stacklevel-1):
+                frame = _next_external_frame(frame)
+                if frame is None:
+                    raise ValueError
     except ValueError:
         globals = sys.__dict__
         lineno = 1
     else:
-        globals = caller.f_globals
-        lineno = caller.f_lineno
+        globals = frame.f_globals
+        lineno = frame.f_lineno
     if '__name__' in globals:
         module = globals['__name__']
     else:
@@ -186,7 +222,7 @@ def warn(message, category=None, stacklevel=1):
     filename = globals.get('__file__')
     if filename:
         fnl = filename.lower()
-        if fnl.endswith((".pyc", ".pyo")):
+        if fnl.endswith(".pyc"):
             filename = filename[:-1]
     else:
         if module == "__main__":
@@ -372,7 +408,6 @@ try:
     defaultaction = _defaultaction
     onceregistry = _onceregistry
     _warnings_defaults = True
-
 except ImportError:
     filters = []
     defaultaction = "default"