Issue #3602

Lib/warnings.py

 """Python part of the warnings subsystem."""
 
 # Note: function level imports should *not* be used
 # in this module as it may cause import lock deadlock.
 # See bug 683658.
 import linecache
 import sys
 import types
 
 __all__ = ["warn", "showwarning", "formatwarning", "filterwarnings",
@@ skipping 248 matching lines @@
         registry[key] = 1
     else:
         # Unrecognized actions are errors
         raise RuntimeError(
               "Unrecognized action (%r) in warnings.filters:\n %s" %
               (action, item))
     # Warn if showwarning() does not support the 'line' argument.
     # Don't use 'inspect' as it relies on an extension module, which break the
     # build thanks to 'warnings' being imported by setup.py.
     fxn_code = None
     if hasattr(showwarning, 'func_code'):

[Benjamin, 2008/08/23 01:46:36]

This stuff is pretty nasty. Can you use inspect?

         fxn_code = showwarning.func_code
     elif hasattr(showwarning, '__func__'):
         fxn_code = showwarning.__func__.func_code
     if fxn_code:
         args = fxn_code.co_varnames[:fxn_code.co_argcount]
-        if 'line' not in args:
+        CO_VARARGS = 0x4
+        if 'line' not in args and not fxn_code.co_flags & CO_VARARGS:
             showwarning_msg = ("functions overriding warnings.showwarning() "
                                 "must support the 'line' argument")
             if message == showwarning_msg:
                 _show_warning(message, category, filename, lineno)
             else:
                 warn(showwarning_msg, DeprecationWarning)
     # Print message and context
     showwarning(message, category, filename, lineno)
+
+
+class WarningMessage(object):

[Benjamin, 2008/08/23 01:46:36]

What happened to the idea of making this a namedtuple?

[brett.cannon, 2008/08/23 02:19:54]

On 2008/08/23 01:46:36, Benjamin wrote:
> What happened to the idea of making this a namedtuple?

Can't import _collections in a svn checkout since 'warnings' is imported before
site.

+
+    """Holds the result of a single showwarning() call."""
+
+    _WARNING_DETAILS = ("message", "category", "filename", "lineno", "file",
+                        "line")
+
+    def __init__(self, message, category, filename, lineno, file=None,
+                    line=None):
+        local_values = locals()
+        for attr in self._WARNING_DETAILS:
+            setattr(self, attr, local_values[attr])
+        self._category_name = category.__name__ if category else None
+
+    def __str__(self):
+        return ("{message : %r, category : %r, filename : %r, lineno : %s, "
+                    "line : %r}" % (self.message, self._category_name,
+                                    self.filename, self.lineno, self.line))
+
+
+class WarningsRecorder(list):
+
+    """Record the result of various showwarning() calls."""
+
+    # Explicitly stated arguments so as to not trigger DeprecationWarning
+    # about adding 'line'.
+    def showwarning(self, *args, **kwargs):
+        self.append(WarningMessage(*args, **kwargs))
+
+    def __getattr__(self, attr):
+        return getattr(self[-1], attr)
+
+    def reset(self):
+        while True:

[Benjamin, 2008/08/23 01:46:36]

Can't this be "del self[:]"?

[brett.cannon, 2008/08/23 02:19:54]

On 2008/08/23 01:46:36, Benjamin wrote:
> Can't this be "del self[:]"?

Yep.

+            try:
+                self.pop()
+            except IndexError:
+                break
+
+
+class catch_warnings(object):

[Benjamin, 2008/08/23 01:46:36]

Shouldn't this be called "catchwarnings"?

[Benjamin, 2008/08/23 01:46:36]

Can't this be a simple generator contextmanager?

[brett.cannon, 2008/08/23 02:19:54]

On 2008/08/23 01:46:36, Benjamin wrote:
> Shouldn't this be called "catchwarnings"?

It's a toss-up thanks to warn_explicit(). I prefer underscores, so I just stuck
with it.

[brett.cannon, 2008/08/23 02:19:54]

On 2008/08/23 01:46:36, Benjamin wrote:
> Can't this be a simple generator contextmanager?

No because _collections can't be imported.

+
+    """Guard the warnings filter from being permanently changed and optionally
+    record the details of any warnings that are issued.
+
+    Context manager returns an instance of warnings.WarningRecorder which is a
+    list of WarningMessage instances. Attributes on WarningRecorder are
+    redirected to the last created WarningMessage instance.
+
+    """
+
+    def __init__(self, record=False, module=None):
+        """Specify whether to record warnings and if an alternative module
+        should be used other than sys.modules['warnings'].
+       
+        For compatibility with Python 3.0, please consider all arguments to be
+        keyword-only.
+        
+        """
+        self._recorder = WarningsRecorder() if record else None
+        self._module = sys.modules['warnings'] if module is None else module
+
+    def __enter__(self):
+        self._filters = self._module.filters
+        self._module.filters = self._filters[:]
+        self._showwarning = self._module.showwarning
+        if self._recorder is not None:
+            self._recorder.reset()  # In case the instance is being reused.
+            self._module.showwarning = self._recorder.showwarning
+        return self._recorder
+
+    def __exit__(self, *exc_info):
+        self._module.filters = self._filters
+        self._module.showwarning = self._showwarning
 
 
 # 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.
@@ skipping 17 matching lines @@
     simplefilter("ignore", category=ImportWarning, append=1)
     bytes_warning = sys.flags.bytes_warning
     if bytes_warning > 1:
         bytes_action = "error"
     elif bytes_warning:
         bytes_action = "default"
     else:
         bytes_action = "ignore"
     simplefilter(bytes_action, category=BytesWarning, append=1)
 del _warnings_defaults