warnings.py

"""Python part of the warnings subsystem."""

import sys

__all__ = ["warn", "warn_explicit", "showwarning",
           "formatwarning", "filterwarnings", "simplefilter",
           "resetwarnings", "catch_warnings"]


def showwarning(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 when run with pythonw.exe - warnings get lost
            return
    try:
        file.write(formatwarning(message, category, filename, lineno, line))
    except OSError:
        pass # the file (probably stderr) is invalid - this warning gets lost.

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)
    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
    return s

def filterwarnings(action, message="", category=Warning, module="", lineno=0,
                   append=False):
    """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, str), "message must be a string"
    assert isinstance(category, type), "category must be a class"
    assert issubclass(category, Warning), "category must be a Warning subclass"
    assert isinstance(module, str), "module must be a string"
    assert isinstance(lineno, int) and lineno >= 0, \
           "lineno must be an int >= 0"
    _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).

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

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 as msg:
            print("Invalid -W option ignored:", msg, file=sys.stderr)

# 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


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."""
    # Check if message is already a Warning object
    if isinstance(message, Warning):
        category = message.__class__
    # Check category argument
    if category is None:
        category = UserWarning
    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:
        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 = frame.f_globals
        lineno = frame.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"):
            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 registry.get('version', 0) != _filters_version:
        registry.clear()
        registry['version'] = _filters_version
    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.
    import linecache
    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))
    if not callable(showwarning):
        raise TypeError("warnings.showwarning() must be set to a "
                        "function or method")
    # 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._module._filters_mutated()
        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._filters_mutated()
        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, _defaultaction, _onceregistry,
                           warn, warn_explicit, _filters_mutated)
    defaultaction = _defaultaction
    onceregistry = _onceregistry
    _warnings_defaults = True
except ImportError:
    filters = []
    defaultaction = "default"
    onceregistry = {}

    _filters_version = 1

    def _filters_mutated():
        global _filters_version
        _filters_version += 1


# Module initialization
_processoptions(sys.warnoptions)
if not _warnings_defaults:
    silence = [ImportWarning, PendingDeprecationWarning]
    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)
    # resource usage warnings are enabled by default in pydebug mode
    if hasattr(sys, 'gettotalrefcount'):
        resource_action = "always"
    else:
        resource_action = "ignore"
    simplefilter(resource_action, category=ResourceWarning, append=1)

del _warnings_defaults