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", "warn_explicit", "showwarning",
           "formatwarning", "filterwarnings", "simplefilter",
           "resetwarnings", "catch_warnings"]


def warnpy3k(message, category=None, stacklevel=1):
    """Issue a deprecation warning for Python 3.x related changes.

    Warnings are omitted unless Python is started with the -3 option.
    """
    if sys.py3kwarning:
        if category is None:
            category = DeprecationWarning
        warn(message, category, stacklevel+1)

def _show_warning(message, category, filename, lineno, file=None, line=None):
    """Hook to write a warning to a file; replace if you like."""
    if file is None:
        file = sys.stderr
        if file is None:
            # sys.stderr is None - warnings get lost
            return
    try:
        file.write(formatwarning(message, category, filename, lineno, line))
    except IOError:
        pass # the file (probably stderr) is invalid - this warning gets lost.
# Keep a working version around in case the deprecation of the old API is
# triggered.
showwarning = _show_warning

def formatwarning(message, category, filename, lineno, line=None):
    """Function to format a warning the standard way."""
    s =  "%s:%s: %s: %s\n" % (filename, lineno, category.__name__, message)
    line = linecache.getline(filename, lineno) if line is None else line
    if line:
        line = line.strip()
        s += "  %s\n" % line
    return s

def filterwarnings(action, message="", category=Warning, module="", lineno=0,
                   append=0):
    """Insert an entry into the list of warnings filters (at the front).

    'action' -- one of "error", "ignore", "always", "default", "module",
                or "once"
    'message' -- a regex that the warning message must match
    'category' -- a class that the warning must be a subclass of
    'module' -- a regex that the module name must match
    'lineno' -- an integer line number, 0 matches all warnings
    'append' -- if true, append to the list of filters
    """
    import re
    assert action in ("error", "ignore", "always", "default", "module",
                      "once"), "invalid action: %r" % (action,)
    assert isinstance(message, basestring), "message must be a string"
    assert isinstance(category, (type, types.ClassType)), \
           "category must be a class"
    assert issubclass(category, Warning), "category must be a Warning subclass"
    assert isinstance(module, basestring), "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)

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.
    'action' -- one of "error", "ignore", "always", "default", "module",
                or "once"
    'category' -- a class that the warning must be a subclass of
    'lineno' -- an integer line number, 0 matches all warnings
    'append' -- if true, append to the list of filters
    """
    assert action in ("error", "ignore", "always", "default", "module",
                      "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:
        filters.insert(0, item)

def resetwarnings():
    """Clear the list of warning filters, so that no filters are active."""
    filters[:] = []

class _OptionError(Exception):
    """Exception used by option processing helpers."""
    pass

# Helper to process -W options passed via sys.warnoptions
def _processoptions(args):
    for arg in args:
        try:
            _setoption(arg)
        except _OptionError, msg:
            print >>sys.stderr, "Invalid -W option ignored:", msg

# Helper for _processoptions()
def _setoption(arg):
    import re
    parts = arg.split(':')
    if len(parts) > 5:
        raise _OptionError("too many fields (max 5): %r" % (arg,))
    while len(parts) < 5:
        parts.append('')
    action, message, category, module, lineno = [s.strip()
                                                 for s in parts]
    action = _getaction(action)
    message = re.escape(message)
    category = _getcategory(category)
    module = re.escape(module)
    if module:
        module = module + '$'
    if lineno:
        try:
            lineno = int(lineno)
            if lineno < 0:
                raise ValueError
        except (ValueError, OverflowError):
            raise _OptionError("invalid lineno %r" % (lineno,))
    else:
        lineno = 0
    filterwarnings(action, message, category, module, lineno)

# Helper for _setoption()
def _getaction(action):
    if not action:
        return "default"
    if action == "all": return "always" # Alias
    for a in ('default', 'always', 'ignore', 'module', 'once', 'error'):
        if a.startswith(action):
            return a
    raise _OptionError("invalid action: %r" % (action,))

# Helper for _setoption()
def _getcategory(category):
    import re
    if not category:
        return Warning
    if re.match("^[a-zA-Z0-9_]+$", category):
        try:
            cat = eval(category)
        except NameError:
            raise _OptionError("unknown warning category: %r" % (category,))
    else:
        i = category.rfind(".")
        module = category[:i]
        klass = category[i+1:]
        try:
            m = __import__(module, None, None, [klass])
        except ImportError:
            raise _OptionError("invalid module name: %r" % (module,))
        try:
            cat = getattr(m, klass)
        except AttributeError:
            raise _OptionError("unknown warning category: %r" % (category,))
    if not issubclass(cat, Warning):
        raise _OptionError("invalid warning category: %r" % (category,))
    return cat


# Code typically replaced by _warnings
def warn(message, category=None, stacklevel=1):
    """Issue a warning, or maybe ignore it or raise an exception."""
    # Check if message is already a Warning object
    if isinstance(message, Warning):
        category = message.__class__
    # Check category argument
    if category is None:
        category = UserWarning
    assert issubclass(category, Warning)
    # Get context information
    try:
        caller = sys._getframe(stacklevel)
    except ValueError:
        globals = sys.__dict__
        lineno = 1
    else:
        globals = caller.f_globals
        lineno = caller.f_lineno
    if '__name__' in globals:
        module = globals['__name__']
    else:
        module = "<string>"
    filename = globals.get('__file__')
    if filename:
        fnl = filename.lower()
        if fnl.endswith((".pyc", ".pyo")):
            filename = filename[:-1]
    else:
        if module == "__main__":
            try:
                filename = sys.argv[0]
            except AttributeError:
                # embedded interpreters don't have sys.argv, see bug #839151
                filename = '__main__'
        if not filename:
            filename = module
    registry = globals.setdefault("__warningregistry__", {})
    warn_explicit(message, category, filename, lineno, module, registry,
                  globals)

def warn_explicit(message, category, filename, lineno,
                  module=None, registry=None, module_globals=None):
    lineno = int(lineno)
    if module is None:
        module = filename or "<unknown>"
        if module[-3:].lower() == ".py":
            module = module[:-3] # XXX What about leading pathname?
    if registry is None:
        registry = {}
    if isinstance(message, Warning):
        text = str(message)
        category = message.__class__
    else:
        text = message
        message = category(message)
    key = (text, category, lineno)
    # Quick test for common case
    if registry.get(key):
        return
    # Search the filters
    for item in filters:
        action, msg, cat, mod, ln = item
        if ((msg is None or msg.match(text)) and
            issubclass(category, cat) and
            (mod is None or mod.match(module)) and
            (ln == 0 or lineno == ln)):
            break
    else:
        action = defaultaction
    # Early exit actions
    if action == "ignore":
        registry[key] = 1
        return

    # Prime the linecache for formatting, in case the
    # "file" is actually in a zipfile or something.
    linecache.getlines(filename, module_globals)

    if action == "error":
        raise message
    # Other actions
    if action == "once":
        registry[key] = 1
        oncekey = (text, category)
        if onceregistry.get(oncekey):
            return
        onceregistry[oncekey] = 1
    elif action == "always":
        pass
    elif action == "module":
        registry[key] = 1
        altkey = (text, category, 0)
        if registry.get(altkey):
            return
        registry[altkey] = 1
    elif action == "default":
        registry[key] = 1
    else:
        # Unrecognized actions are errors
        raise RuntimeError(
              "Unrecognized action (%r) in warnings.filters:\n %s" %
              (action, item))
    # Print message and context
    showwarning(message, category, filename, lineno)


class WarningMessage(object):

    """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 catch_warnings(object):

    """A context manager that copies and restores the warnings filter upon
    exiting the context.

    The 'record' argument specifies whether warnings should be captured by a
    custom implementation of warnings.showwarning() and be appended to a list
    returned by the context manager. Otherwise None is returned by the context
    manager. The objects appended to the list are arguments whose attributes
    mirror the arguments to showwarning().

    The 'module' argument is to specify an alternative module to the module
    named 'warnings' and imported under that name. This argument is only useful
    when testing the warnings module itself.

    """

    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._record = record
        self._module = sys.modules['warnings'] if module is None else module
        self._entered = False

    def __repr__(self):
        args = []
        if self._record:
            args.append("record=True")
        if self._module is not sys.modules['warnings']:
            args.append("module=%r" % self._module)
        name = type(self).__name__
        return "%s(%s)" % (name, ", ".join(args))

    def __enter__(self):
        if self._entered:
            raise RuntimeError("Cannot enter %r twice" % self)
        self._entered = True
        self._filters = self._module.filters
        self._module.filters = self._filters[:]
        self._showwarning = self._module.showwarning
        if self._record:
            log = []
            def showwarning(*args, **kwargs):
                log.append(WarningMessage(*args, **kwargs))
            self._module.showwarning = showwarning
            return log
        else:
            return None

    def __exit__(self, *exc_info):
        if not self._entered:
            raise RuntimeError("Cannot exit %r without entering first" % self)
        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.
_warnings_defaults = False
try:
    from _warnings import (filters, default_action, once_registry,
                            warn, warn_explicit)
    defaultaction = default_action
    onceregistry = once_registry
    _warnings_defaults = True
except ImportError:
    filters = []
    defaultaction = "default"
    onceregistry = {}


# Module initialization
_processoptions(sys.warnoptions)
if not _warnings_defaults:
    silence = [ImportWarning, PendingDeprecationWarning]
    # Don't silence DeprecationWarning if -3 or -Q was used.
    if not sys.py3kwarning and not sys.flags.division_warning:
        silence.append(DeprecationWarning)
    for cls in silence:
        simplefilter("ignore", category=cls)
    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