# -*- 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}.
"""
from __future__ import division, absolute_import, print_function
# System Imports
import sys
import linecache
import inspect
import opcode
from inspect import getmro
from twisted.python import reflect
from twisted.python.compat import _PY3, NativeStringIO as StringIO
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(BaseException):
"""
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.
# on PY3, b'a'[0] == 97 while in py2 b'a'[0] == b'a' opcodes
# are stored in bytes so we need to properly account for this
# difference.
if _PY3:
_yieldOpcode = opcode.opmap["YIELD_VALUE"]
else:
_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 L{None} are allowed.
If L{None} is supplied for C{exc_value}, the value of C{exc_tb} is
ignored, otherwise if C{exc_tb} is L{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
if isinstance(exc_value, str) and exc_type is None:
raise TypeError("Strings are not supported by Failure")
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
elif getattr(self.value, "__traceback__", None):
# Python 3
tb = self.value.__traceback__
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 = list(localz.items())
globalz = list(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 = list(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. In Python 2 the Failure will be
raised; in Python 3 the underlying exception will be re-raised.
@type errorTypes: L{Exception}
"""
error = self.check(*errorTypes)
if not error:
self.raiseException()
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
# It would be nice to use twisted.python.compat.reraise, but that breaks
# the stack exploration in _findFailure; possibly this can be fixed in
# #5931.
if getattr(BaseException, "with_traceback", None):
# Python 3
def raiseException(self):
raise self.value.with_traceback(self.tb)
else:
exec("""def raiseException(self):
raise self.type, self.value, self.tb""")
raiseException.__doc__ = (
"""
raise the original exception, preserving traceback
information if available.
""")
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.
"""
# Note that the actual magic to find the traceback information
# is done in _findFailure.
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.__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.__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.__code__:
return frame.f_locals.get('self')
_findFailure = classmethod(_findFailure)
def __repr__(self):
return "<%s %s: %s>" % (reflect.qual(self.__class__),
reflect.qual(self.type),
self.getErrorMessage())
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.
On Python 3, this will also set the C{__traceback__} attribute of the
exception instance to L{None}.
"""
self.__dict__ = self.__getstate__()
if getattr(self.value, "__traceback__", None):
# Python 3
self.value.__traceback__ = None
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:
from twisted.python import log
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':
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__):
"""
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