Change warnings to avoid importing re module during startup.

Add API function simplefilter() that does not create or install
regular expressions to match message or module.  Extend the filters
data structure to store None as an alternative to re.compile("").

Move the _test() function to test_warnings and add some code to try
and avoid disturbing the global state of the warnings module.

Lib/test/output/test_warnings

+test_warnings
+('ignore', False, 'FutureWarning', False, 0)
+('ignore', True, 'OverflowWarning', True, 0)
+('ignore', True, 'PendingDeprecationWarning', True, 0)
+Lib/test/test_warnings.py:31: UserWarning: hello world
+Lib/test/test_warnings.py:32: UserWarning: hello world
+Lib/test/test_warnings.py:33: DeprecationWarning: hello world
+Lib/test/test_warnings.py:35: UserWarning: hello world
+Caught UserWarning: hello world
+Caught AssertionError: invalid action: 'booh'

Lib/test/test_warnings.py

+import warnings
+
+# The warnings module isn't easily tested, because it relies on module
+# globals to store configuration information.  We need to extract the
+# current settings to avoid bashing them while running tests.
+
+_filters = []
+_showwarning = None
+
+def showwarning(message, category, filename, lineno, file=None):
+    i = filename.find("Lib/")
+    filename = filename[i:]
+    print "%s:%s: %s: %s" % (filename, lineno, category.__name__, message)
+
+def monkey():
+    global _filters, _showwarning
+    _filters = warnings.filters[:]
+    _showwarning = warnings.showwarning
+    warnings.showwarning = showwarning
+
+def unmonkey():
+    warnings.filters = _filters[:]
+    warnings.showwarning = _showwarning
+
+def test():
+    for item in warnings.filters:
+        print (item[0], item[1] is None, item[2].__name__, item[3] is None,
+               item[4])
+    hello = "hello world"
+    for i in range(4):
+        warnings.warn(hello)
+    warnings.warn(hello, UserWarning)
+    warnings.warn(hello, DeprecationWarning)
+    for i in range(3):
+        warnings.warn(hello)
+    warnings.filterwarnings("error", "", Warning, "", 0)
+    try:
+        warnings.warn(hello)
+    except Exception, msg:
+        print "Caught", msg.__class__.__name__ + ":", msg
+    else:
+        print "No exception"
+    warnings.resetwarnings()
+    try:
+        warnings.filterwarnings("booh", "", Warning, "", 0)
+    except Exception, msg:
+        print "Caught", msg.__class__.__name__ + ":", msg
+    else:
+        print "No exception"
+
+monkey()
+test()
+unmonkey()

Lib/warnings.py

@@ -9,8 +9,16 @@ import linecache
 __all__ = ["warn", "showwarning", "formatwarning", "filterwarnings",
            "resetwarnings"]
 
-defaultaction = "default"
+# filters contains a sequence of filter 5-tuples
+# The components of the 5-tuple are:
+# - an action: error, ignore, always, default, module, or once
+# - a compiled regex that must match the warning message
+# - a class representing the warning category
+# - a compiled regex that must match the module that is being warned
+# - a line number for the line being warning, or 0 to mean any line
+# If either if the compiled regexs are None, match anything.
 filters = []
+defaultaction = "default"
 onceregistry = {}
 
 def warn(message, category=None, stacklevel=1):
@@ -69,9 +77,9 @@ def warn_explicit(message, category, filename, lineno,
     # Search the filters
     for item in filters:
         action, msg, cat, mod, ln = item
-        if (msg.match(text) and
+        if ((msg is None or msg.match(text)) and
             issubclass(category, cat) and
-            mod.match(module) and
+            (msg is None or mod.match(module)) and
             (ln == 0 or lineno == ln)):
             break
     else:
@@ -145,6 +153,21 @@ def filterwarnings(action, message="", category=Warning, module="", lineno=0,
     else:
         filters.insert(0, item)
 
+def simplefilter(action, category=Warning, lineno=0, append=0):
+    """Insert a simple entry into the list of warnings filters (at the front).
+
+    A simple filter matches all modules and messages.
+    """
+    assert action in ("error", "ignore", "always", "default", "module",
+                      "once"), "invalid action: %s" % `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:
+        filters.insert(0, item)
+
 def resetwarnings():
     """Clear the list of warning filters, so that no filters are active."""
     filters[:] = []
@@ -225,44 +248,6 @@ def _getcategory(category):
         raise _OptionError("invalid warning category: %s" % `category`)
     return cat
 
-# Self-test
-def _test():
-    import getopt
-    testoptions = []
-    try:
-        opts, args = getopt.getopt(sys.argv[1:], "W:")
-    except getopt.error, msg:
-        print >>sys.stderr, msg
-        return
-    for o, a in opts:
-        testoptions.append(a)
-    try:
-        _processoptions(testoptions)
-    except _OptionError, msg:
-        print >>sys.stderr, msg
-        return
-    for item in filters: print item
-    hello = "hello world"
-    warn(hello); warn(hello); warn(hello); warn(hello)
-    warn(hello, UserWarning)
-    warn(hello, DeprecationWarning)
-    for i in range(3):
-        warn(hello)
-    filterwarnings("error", "", Warning, "", 0)
-    try:
-        warn(hello)
-    except Exception, msg:
-        print "Caught", msg.__class__.__name__ + ":", msg
-    else:
-        print "No exception"
-    resetwarnings()
-    try:
-        filterwarnings("booh", "", Warning, "", 0)
-    except Exception, msg:
-        print "Caught", msg.__class__.__name__ + ":", msg
-    else:
-        print "No exception"
-
 # Module initialization
 if __name__ == "__main__":
     import __main__
@@ -270,5 +255,5 @@ if __name__ == "__main__":
     _test()
 else:
     _processoptions(sys.warnoptions)
-    filterwarnings("ignore", category=OverflowWarning, append=1)
-    filterwarnings("ignore", category=PendingDeprecationWarning, append=1)
+    simplefilter("ignore", category=OverflowWarning, append=1)
+    simplefilter("ignore", category=PendingDeprecationWarning, append=1)