path: root/lib/python2.7/site-packages/Twisted-12.2.0-py2.7-linux-x86_64.egg/twisted/python/failure.py

# -*- test-case-name: twisted.test.test_failure -*-
# See also test suite twisted.test.test_pbfailure

# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.


"""
Asynchronous-friendly error mechanism.

See L{Failure}.
"""

# System Imports
import sys
import linecache
import inspect
import opcode
from cStringIO import StringIO
from inspect import getmro

from twisted.python import reflect

count = 0
traceupLength = 4

class DefaultException(Exception):
    pass

def format_frames(frames, write, detail="default"):
    """Format and write frames.

    @param frames: is a list of frames as used by Failure.frames, with
        each frame being a list of
        (funcName, fileName, lineNumber, locals.items(), globals.items())
    @type frames: list
    @param write: this will be called with formatted strings.
    @type write: callable
    @param detail: Four detail levels are available:
        default, brief, verbose, and verbose-vars-not-captured.
        C{Failure.printDetailedTraceback} uses the latter when the caller asks
        for verbose, but no vars were captured, so that an explicit warning
        about the missing data is shown.
    @type detail: string
    """
    if detail not in ('default', 'brief', 'verbose',
                      'verbose-vars-not-captured'):
        raise ValueError(
            "Detail must be default, brief, verbose, or "
            "verbose-vars-not-captured. (not %r)" % (detail,))
    w = write
    if detail == "brief":
        for method, filename, lineno, localVars, globalVars in frames:
            w('%s:%s:%s\n' % (filename, lineno, method))
    elif detail == "default":
        for method, filename, lineno, localVars, globalVars in frames:
            w( '  File "%s", line %s, in %s\n' % (filename, lineno, method))
            w( '    %s\n' % linecache.getline(filename, lineno).strip())
    elif detail == "verbose-vars-not-captured":
        for method, filename, lineno, localVars, globalVars in frames:
            w("%s:%d: %s(...)\n" % (filename, lineno, method))
        w(' [Capture of Locals and Globals disabled (use captureVars=True)]\n')
    elif detail == "verbose":
        for method, filename, lineno, localVars, globalVars in frames:
            w("%s:%d: %s(...)\n" % (filename, lineno, method))
            w(' [ Locals ]\n')
            # Note: the repr(val) was (self.pickled and val) or repr(val)))
            for name, val in localVars:
                w("  %s : %s\n" %  (name, repr(val)))
            w(' ( Globals )\n')
            for name, val in globalVars:
                w("  %s : %s\n" %  (name, repr(val)))

# slyphon: i have a need to check for this value in trial
#          so I made it a module-level constant
EXCEPTION_CAUGHT_HERE = "--- <exception caught here> ---"



class NoCurrentExceptionError(Exception):
    """
    Raised when trying to create a Failure from the current interpreter
    exception state and there is no current exception state.
    """


class _Traceback(object):
    """
    Fake traceback object which can be passed to functions in the standard
    library L{traceback} module.
    """

    def __init__(self, frames):
        """
        Construct a fake traceback object using a list of frames. Note that
        although frames generally include locals and globals, this information
        is not kept by this object, since locals and globals are not used in
        standard tracebacks.

        @param frames: [(methodname, filename, lineno, locals, globals), ...]
        """
        assert len(frames) > 0, "Must pass some frames"
        head, frames = frames[0], frames[1:]
        name, filename, lineno, localz, globalz = head
        self.tb_frame = _Frame(name, filename)
        self.tb_lineno = lineno
        if len(frames) == 0:
            self.tb_next = None
        else:
            self.tb_next = _Traceback(frames)


class _Frame(object):
    """
    A fake frame object, used by L{_Traceback}.

    @ivar f_code: fake L{code<types.CodeType>} object
    @ivar f_globals: fake f_globals dictionary (usually empty)
    @ivar f_locals: fake f_locals dictionary (usually empty)
    """

    def __init__(self, name, filename):
        """
        @param name: method/function name for this frame.
        @type name: C{str}
        @param filename: filename for this frame.
        @type name: C{str}
        """
        self.f_code = _Code(name, filename)
        self.f_globals = {}
        self.f_locals = {}


class _Code(object):
    """
    A fake code object, used by L{_Traceback} via L{_Frame}.
    """
    def __init__(self, name, filename):
        self.co_name = name
        self.co_filename = filename


class Failure:
    """
    A basic abstraction for an error that has occurred.

    This is necessary because Python's built-in error mechanisms are
    inconvenient for asynchronous communication.

    The C{stack} and C{frame} attributes contain frames.  Each frame is a tuple
    of (funcName, fileName, lineNumber, localsItems, globalsItems), where
    localsItems and globalsItems are the contents of
    C{locals().items()}/C{globals().items()} for that frame, or an empty tuple
    if those details were not captured.

    @ivar value: The exception instance responsible for this failure.
    @ivar type: The exception's class.
    @ivar stack: list of frames, innermost last, excluding C{Failure.__init__}.
    @ivar frames: list of frames, innermost first.
    """

    pickled = 0
    stack = None

    # The opcode of "yield" in Python bytecode. We need this in _findFailure in
    # order to identify whether an exception was thrown by a
    # throwExceptionIntoGenerator.
    _yieldOpcode = chr(opcode.opmap["YIELD_VALUE"])

    def __init__(self, exc_value=None, exc_type=None, exc_tb=None,
                 captureVars=False):
        """
        Initialize me with an explanation of the error.

        By default, this will use the current C{exception}
        (L{sys.exc_info}()).  However, if you want to specify a
        particular kind of failure, you can pass an exception as an
        argument.

        If no C{exc_value} is passed, then an "original" C{Failure} will
        be searched for. If the current exception handler that this
        C{Failure} is being constructed in is handling an exception
        raised by L{raiseException}, then this C{Failure} will act like
        the original C{Failure}.

        For C{exc_tb} only L{traceback} instances or C{None} are allowed.
        If C{None} is supplied for C{exc_value}, the value of C{exc_tb} is
        ignored, otherwise if C{exc_tb} is C{None}, it will be found from
        execution context (ie, L{sys.exc_info}).

        @param captureVars: if set, capture locals and globals of stack
            frames.  This is pretty slow, and makes no difference unless you
            are going to use L{printDetailedTraceback}.
        """
        global count
        count = count + 1
        self.count = count
        self.type = self.value = tb = None
        self.captureVars = captureVars

        #strings Exceptions/Failures are bad, mmkay?
        if isinstance(exc_value, (str, unicode)) and exc_type is None:
            import warnings
            warnings.warn(
                "Don't pass strings (like %r) to failure.Failure (replacing with a DefaultException)." %
                exc_value, DeprecationWarning, stacklevel=2)
            exc_value = DefaultException(exc_value)

        stackOffset = 0

        if exc_value is None:
            exc_value = self._findFailure()

        if exc_value is None:
            self.type, self.value, tb = sys.exc_info()
            if self.type is None:
                raise NoCurrentExceptionError()
            stackOffset = 1
        elif exc_type is None:
            if isinstance(exc_value, Exception):
                self.type = exc_value.__class__
            else: #allow arbitrary objects.
                self.type = type(exc_value)
            self.value = exc_value
        else:
            self.type = exc_type
            self.value = exc_value
        if isinstance(self.value, Failure):
            self.__dict__ = self.value.__dict__
            return
        if tb is None:
            if exc_tb:
                tb = exc_tb
#             else:
#                 log.msg("Erf, %r created with no traceback, %s %s." % (
#                     repr(self), repr(exc_value), repr(exc_type)))
#                 for s in traceback.format_stack():
#                     log.msg(s)

        frames = self.frames = []
        stack = self.stack = []

        # added 2003-06-23 by Chris Armstrong. Yes, I actually have a
        # use case where I need this traceback object, and I've made
        # sure that it'll be cleaned up.
        self.tb = tb

        if tb:
            f = tb.tb_frame
        elif not isinstance(self.value, Failure):
            # we don't do frame introspection since it's expensive,
            # and if we were passed a plain exception with no
            # traceback, it's not useful anyway
            f = stackOffset = None

        while stackOffset and f:
            # This excludes this Failure.__init__ frame from the
            # stack, leaving it to start with our caller instead.
            f = f.f_back
            stackOffset -= 1

        # Keeps the *full* stack.  Formerly in spread.pb.print_excFullStack:
        #
        #   The need for this function arises from the fact that several
        #   PB classes have the peculiar habit of discarding exceptions
        #   with bareword "except:"s.  This premature exception
        #   catching means tracebacks generated here don't tend to show
        #   what called upon the PB object.

        while f:
            if captureVars:
                localz = f.f_locals.copy()
                if f.f_locals is f.f_globals:
                    globalz = {}
                else:
                    globalz = f.f_globals.copy()
                for d in globalz, localz:
                    if "__builtins__" in d:
                        del d["__builtins__"]
                localz = localz.items()
                globalz = globalz.items()
            else:
                localz = globalz = ()
            stack.insert(0, (
                f.f_code.co_name,
                f.f_code.co_filename,
                f.f_lineno,
                localz,
                globalz,
                ))
            f = f.f_back

        while tb is not None:
            f = tb.tb_frame
            if captureVars:
                localz = f.f_locals.copy()
                if f.f_locals is f.f_globals:
                    globalz = {}
                else:
                    globalz = f.f_globals.copy()
                for d in globalz, localz:
                    if "__builtins__" in d:
                        del d["__builtins__"]
                localz = localz.items()
                globalz = globalz.items()
            else:
                localz = globalz = ()
            frames.append((
                f.f_code.co_name,
                f.f_code.co_filename,
                tb.tb_lineno,
                localz,
                globalz,
                ))
            tb = tb.tb_next
        if inspect.isclass(self.type) and issubclass(self.type, Exception):
            parentCs = getmro(self.type)
            self.parents = map(reflect.qual, parentCs)
        else:
            self.parents = [self.type]

    def trap(self, *errorTypes):
        """Trap this failure if its type is in a predetermined list.

        This allows you to trap a Failure in an error callback.  It will be
        automatically re-raised if it is not a type that you expect.

        The reason for having this particular API is because it's very useful
        in Deferred errback chains::

            def _ebFoo(self, failure):
                r = failure.trap(Spam, Eggs)
                print 'The Failure is due to either Spam or Eggs!'
                if r == Spam:
                    print 'Spam did it!'
                elif r == Eggs:
                    print 'Eggs did it!'

        If the failure is not a Spam or an Eggs, then the Failure
        will be 'passed on' to the next errback.

        @type errorTypes: L{Exception}
        """
        error = self.check(*errorTypes)
        if not error:
            raise self
        return error

    def check(self, *errorTypes):
        """Check if this failure's type is in a predetermined list.

        @type errorTypes: list of L{Exception} classes or
                          fully-qualified class names.
        @returns: the matching L{Exception} type, or None if no match.
        """
        for error in errorTypes:
            err = error
            if inspect.isclass(error) and issubclass(error, Exception):
                err = reflect.qual(error)
            if err in self.parents:
                return error
        return None


    def raiseException(self):
        """
        raise the original exception, preserving traceback
        information if available.
        """
        raise self.type, self.value, self.tb


    def throwExceptionIntoGenerator(self, g):
        """
        Throw the original exception into the given generator,
        preserving traceback information if available.

        @return: The next value yielded from the generator.
        @raise StopIteration: If there are no more values in the generator.
        @raise anything else: Anything that the generator raises.
        """
        return g.throw(self.type, self.value, self.tb)


    def _findFailure(cls):
        """
        Find the failure that represents the exception currently in context.
        """
        tb = sys.exc_info()[-1]
        if not tb:
            return

        secondLastTb = None
        lastTb = tb
        while lastTb.tb_next:
            secondLastTb = lastTb
            lastTb = lastTb.tb_next

        lastFrame = lastTb.tb_frame

        # NOTE: f_locals.get('self') is used rather than
        # f_locals['self'] because psyco frames do not contain
        # anything in their locals() dicts.  psyco makes debugging
        # difficult anyhow, so losing the Failure objects (and thus
        # the tracebacks) here when it is used is not that big a deal.

        # handle raiseException-originated exceptions
        if lastFrame.f_code is cls.raiseException.func_code:
            return lastFrame.f_locals.get('self')

        # handle throwExceptionIntoGenerator-originated exceptions
        # this is tricky, and differs if the exception was caught
        # inside the generator, or above it:

        # it is only really originating from
        # throwExceptionIntoGenerator if the bottom of the traceback
        # is a yield.
        # Pyrex and Cython extensions create traceback frames
        # with no co_code, but they can't yield so we know it's okay to just return here.
        if ((not lastFrame.f_code.co_code) or
            lastFrame.f_code.co_code[lastTb.tb_lasti] != cls._yieldOpcode):
            return

        # if the exception was caught above the generator.throw
        # (outside the generator), it will appear in the tb (as the
        # second last item):
        if secondLastTb:
            frame = secondLastTb.tb_frame
            if frame.f_code is cls.throwExceptionIntoGenerator.func_code:
                return frame.f_locals.get('self')

        # if the exception was caught below the generator.throw
        # (inside the generator), it will appear in the frames' linked
        # list, above the top-level traceback item (which must be the
        # generator frame itself, thus its caller is
        # throwExceptionIntoGenerator).
        frame = tb.tb_frame.f_back
        if frame and frame.f_code is cls.throwExceptionIntoGenerator.func_code:
            return frame.f_locals.get('self')

    _findFailure = classmethod(_findFailure)

    def __repr__(self):
        return "<%s %s>" % (self.__class__, self.type)

    def __str__(self):
        return "[Failure instance: %s]" % self.getBriefTraceback()

    def __getstate__(self):
        """Avoid pickling objects in the traceback.
        """
        if self.pickled:
            return self.__dict__
        c = self.__dict__.copy()

        c['frames'] = [
            [
                v[0], v[1], v[2],
                _safeReprVars(v[3]),
                _safeReprVars(v[4]),
            ] for v in self.frames
        ]

        # added 2003-06-23. See comment above in __init__
        c['tb'] = None

        if self.stack is not None:
            # XXX: This is a band-aid.  I can't figure out where these
            # (failure.stack is None) instances are coming from.
            c['stack'] = [
                [
                    v[0], v[1], v[2],
                    _safeReprVars(v[3]),
                    _safeReprVars(v[4]),
                ] for v in self.stack
            ]

        c['pickled'] = 1
        return c

    def cleanFailure(self):
        """Remove references to other objects, replacing them with strings.
        """
        self.__dict__ = self.__getstate__()

    def getTracebackObject(self):
        """
        Get an object that represents this Failure's stack that can be passed
        to traceback.extract_tb.

        If the original traceback object is still present, return that. If this
        traceback object has been lost but we still have the information,
        return a fake traceback object (see L{_Traceback}). If there is no
        traceback information at all, return None.
        """
        if self.tb is not None:
            return self.tb
        elif len(self.frames) > 0:
            return _Traceback(self.frames)
        else:
            return None

    def getErrorMessage(self):
        """Get a string of the exception which caused this Failure."""
        if isinstance(self.value, Failure):
            return self.value.getErrorMessage()
        return reflect.safe_str(self.value)

    def getBriefTraceback(self):
        io = StringIO()
        self.printBriefTraceback(file=io)
        return io.getvalue()

    def getTraceback(self, elideFrameworkCode=0, detail='default'):
        io = StringIO()
        self.printTraceback(file=io, elideFrameworkCode=elideFrameworkCode, detail=detail)
        return io.getvalue()


    def printTraceback(self, file=None, elideFrameworkCode=False, detail='default'):
        """
        Emulate Python's standard error reporting mechanism.

        @param file: If specified, a file-like object to which to write the
            traceback.

        @param elideFrameworkCode: A flag indicating whether to attempt to
            remove uninteresting frames from within Twisted itself from the
            output.

        @param detail: A string indicating how much information to include
            in the traceback.  Must be one of C{'brief'}, C{'default'}, or
            C{'verbose'}.
        """
        if file is None:
            file = log.logerr
        w = file.write

        if detail == 'verbose' and not self.captureVars:
            # We don't have any locals or globals, so rather than show them as
            # empty make the output explicitly say that we don't have them at
            # all.
            formatDetail = 'verbose-vars-not-captured'
        else:
            formatDetail = detail

        # Preamble
        if detail == 'verbose':
            w( '*--- Failure #%d%s---\n' %
               (self.count,
                (self.pickled and ' (pickled) ') or ' '))
        elif detail == 'brief':
            if self.frames:
                hasFrames = 'Traceback'
            else:
                hasFrames = 'Traceback (failure with no frames)'
            w("%s: %s: %s\n" % (
                    hasFrames,
                    reflect.safe_str(self.type),
                    reflect.safe_str(self.value)))
        else:
            w( 'Traceback (most recent call last):\n')

        # Frames, formatted in appropriate style
        if self.frames:
            if not elideFrameworkCode:
                format_frames(self.stack[-traceupLength:], w, formatDetail)
                w("%s\n" % (EXCEPTION_CAUGHT_HERE,))
            format_frames(self.frames, w, formatDetail)
        elif not detail == 'brief':
            # Yeah, it's not really a traceback, despite looking like one...
            w("Failure: ")

        # postamble, if any
        if not detail == 'brief':
            # Unfortunately, self.type will not be a class object if this
            # Failure was created implicitly from a string exception.
            # qual() doesn't make any sense on a string, so check for this
            # case here and just write out the string if that's what we
            # have.
            if isinstance(self.type, (str, unicode)):
                w(self.type + "\n")
            else:
                w("%s: %s\n" % (reflect.qual(self.type),
                                reflect.safe_str(self.value)))
        # chaining
        if isinstance(self.value, Failure):
            # TODO: indentation for chained failures?
            file.write(" (chained Failure)\n")
            self.value.printTraceback(file, elideFrameworkCode, detail)
        if detail == 'verbose':
            w('*--- End of Failure #%d ---\n' % self.count)


    def printBriefTraceback(self, file=None, elideFrameworkCode=0):
        """Print a traceback as densely as possible.
        """
        self.printTraceback(file, elideFrameworkCode, detail='brief')

    def printDetailedTraceback(self, file=None, elideFrameworkCode=0):
        """Print a traceback with detailed locals and globals information.
        """
        self.printTraceback(file, elideFrameworkCode, detail='verbose')


def _safeReprVars(varsDictItems):
    """
    Convert a list of (name, object) pairs into (name, repr) pairs.

    L{twisted.python.reflect.safe_repr} is used to generate the repr, so no
    exceptions will be raised by faulty C{__repr__} methods.

    @param varsDictItems: a sequence of (name, value) pairs as returned by e.g.
        C{locals().items()}.
    @returns: a sequence of (name, repr) pairs.
    """
    return [(name, reflect.safe_repr(obj)) for (name, obj) in varsDictItems]


# slyphon: make post-morteming exceptions tweakable

DO_POST_MORTEM = True

def _debuginit(self, exc_value=None, exc_type=None, exc_tb=None,
               captureVars=False,
               Failure__init__=Failure.__init__.im_func):
    """
    Initialize failure object, possibly spawning pdb.
    """
    if (exc_value, exc_type, exc_tb) == (None, None, None):
        exc = sys.exc_info()
        if not exc[0] == self.__class__ and DO_POST_MORTEM:
            try:
                strrepr = str(exc[1])
            except:
                strrepr = "broken str"
            print "Jumping into debugger for post-mortem of exception '%s':" % (strrepr,)
            import pdb
            pdb.post_mortem(exc[2])
    Failure__init__(self, exc_value, exc_type, exc_tb, captureVars)


def startDebugMode():
    """Enable debug hooks for Failures."""
    Failure.__init__ = _debuginit


# Sibling imports - at the bottom and unqualified to avoid unresolvable
# circularity
import log