Source code for boltons.tbutils

# -*- coding: utf-8 -*-
"""One of the oft-cited tenets of Python is that it is better to ask
forgiveness than permission. That is, there are many cases where it is
more inclusive and correct to handle exceptions than spend extra lines
and execution time checking for conditions. This philosophy makes good
exception handling features all the more important. Unfortunately
Python's :mod:`traceback` module is woefully behind the times.

The ``tbutils`` module provides two disparate but complementary featuresets:

  1. With :class:`ExceptionInfo` and :class:`TracebackInfo`, the
     ability to extract, construct, manipulate, format, and serialize
     exceptions, tracebacks, and callstacks.
  2. With :class:`ParsedException`, the ability to find and parse tracebacks
     from captured output such as logs and stdout.

There is also the :class:`ContextualTracebackInfo` variant of
:class:`TracebackInfo`, which includes much more information from each
frame of the callstack, including values of locals and neighboring
lines of code.

from __future__ import print_function

import re
import sys
import linecache

    text = unicode  # Python 2
except NameError:
    text = str      # Python 3

# TODO: chaining primitives?  what are real use cases where these help?

# TODO: print_* for backwards compatibility
# __all__ = ['extract_stack', 'extract_tb', 'format_exception',
#            'format_exception_only', 'format_list', 'format_stack',
#            'format_tb', 'print_exc', 'format_exc', 'print_exception',
#            'print_last', 'print_stack', 'print_tb']

__all__ = ['ExceptionInfo', 'TracebackInfo', 'Callpoint',
           'ContextualExceptionInfo', 'ContextualTracebackInfo',
           'ContextualCallpoint', 'print_exception', 'ParsedException']

[docs]class Callpoint(object): """The Callpoint is a lightweight object used to represent a single entry in the code of a call stack. It stores the code-related metadata of a given frame. Available attributes are the same as the parameters below. Args: func_name (str): the function name lineno (int): the line number module_name (str): the module name module_path (str): the filesystem path of the module lasti (int): the index of bytecode execution line (str): the single-line code content (if available) """ __slots__ = ('func_name', 'lineno', 'module_name', 'module_path', 'lasti', 'line') def __init__(self, module_name, module_path, func_name, lineno, lasti, line=None): self.func_name = func_name self.lineno = lineno self.module_name = module_name self.module_path = module_path self.lasti = lasti self.line = line
[docs] def to_dict(self): "Get a :class:`dict` copy of the Callpoint. Useful for serialization." ret = {} for slot in self.__slots__: try: val = getattr(self, slot) except AttributeError: pass else: ret[slot] = str(val) if isinstance(val, _DeferredLine) else val return ret
[docs] @classmethod def from_current(cls, level=1): "Creates a Callpoint from the location of the calling function." frame = sys._getframe(level) return cls.from_frame(frame)
[docs] @classmethod def from_frame(cls, frame): "Create a Callpoint object from data extracted from the given frame." func_name = frame.f_code.co_name lineno = frame.f_lineno module_name = frame.f_globals.get('__name__', '') module_path = frame.f_code.co_filename lasti = frame.f_lasti line = _DeferredLine(module_path, lineno, frame.f_globals) return cls(module_name, module_path, func_name, lineno, lasti, line=line)
[docs] @classmethod def from_tb(cls, tb): """Create a Callpoint from the traceback of the current exception. Main difference with :meth:`from_frame` is that ``lineno`` and ``lasti`` come from the traceback, which is to say the line that failed in the try block, not the line currently being executed (in the except block). """ func_name = tb.tb_frame.f_code.co_name lineno = tb.tb_lineno lasti = tb.tb_lasti module_name = tb.tb_frame.f_globals.get('__name__', '') module_path = tb.tb_frame.f_code.co_filename line = _DeferredLine(module_path, lineno, tb.tb_frame.f_globals) return cls(module_name, module_path, func_name, lineno, lasti, line=line)
def __repr__(self): cn = self.__class__.__name__ args = [getattr(self, s, None) for s in self.__slots__] if not any(args): return super(Callpoint, self).__repr__() else: return '%s(%s)' % (cn, ', '.join([repr(a) for a in args]))
[docs] def tb_frame_str(self): """Render the Callpoint as it would appear in a standard printed Python traceback. Returns a string with filename, line number, function name, and the actual code line of the error on up to two lines. """ ret = ' File "%s", line %s, in %s\n' % (self.module_path, self.lineno, self.func_name) if self.line: ret += ' %s\n' % (str(self.line).strip(),) return ret
class _DeferredLine(object): """The _DeferredLine type allows Callpoints and TracebackInfos to be constructed without potentially hitting the filesystem, as is the normal behavior of the standard Python :mod:`traceback` and :mod:`linecache` modules. Calling :func:`str` fetches and caches the line. Args: filename (str): the path of the file containing the line lineno (int): the number of the line in question module_globals (dict): an optional dict of module globals, used to handle advanced use cases using custom module loaders. """ __slots__ = ('filename', 'lineno', '_line', '_mod_name', '_mod_loader') def __init__(self, filename, lineno, module_globals=None): self.filename = filename self.lineno = lineno # TODO: this is going away when we fix linecache # TODO: (mark) read about loader if module_globals is None: self._mod_name = None self._mod_loader = None else: self._mod_name = module_globals.get('__name__') self._mod_loader = module_globals.get('__loader__') def __eq__(self, other): return (self.lineno, self.filename) == (other.lineno, other.filename) def __ne__(self, other): return not self == other def __str__(self): ret = getattr(self, '_line', None) if ret is not None: return ret try: linecache.checkcache(self.filename) mod_globals = {'__name__': self._mod_name, '__loader__': self._mod_loader} line = linecache.getline(self.filename, self.lineno, mod_globals) line = line.rstrip() except KeyError: line = '' self._line = line return line def __repr__(self): return repr(str(self)) def __len__(self): return len(str(self)) # TODO: dedup frames, look at __eq__ on _DeferredLine
[docs]class TracebackInfo(object): """The TracebackInfo class provides a basic representation of a stack trace, be it from an exception being handled or just part of normal execution. It is basically a wrapper around a list of :class:`Callpoint` objects representing frames. Args: frames (list): A list of frame objects in the stack. .. note :: ``TracebackInfo`` can represent both exception tracebacks and non-exception tracebacks (aka stack traces). As a result, there is no ``TracebackInfo.from_current()``, as that would be ambiguous. Instead, call :meth:`TracebackInfo.from_frame` without the *frame* argument for a stack trace, or :meth:`TracebackInfo.from_traceback` without the *tb* argument for an exception traceback. """ callpoint_type = Callpoint def __init__(self, frames): self.frames = frames
[docs] @classmethod def from_frame(cls, frame=None, level=1, limit=None): """Create a new TracebackInfo *frame* by recurring up in the stack a max of *limit* times. If *frame* is unset, get the frame from :func:`sys._getframe` using *level*. Args: frame (types.FrameType): frame object from :func:`sys._getframe` or elsewhere. Defaults to result of :func:`sys.get_frame`. level (int): If *frame* is unset, the desired frame is this many levels up the stack from the invocation of this method. Default ``1`` (i.e., caller of this method). limit (int): max number of parent frames to extract (defaults to :data:`sys.tracebacklimit`) """ ret = [] if frame is None: frame = sys._getframe(1) if limit is None: limit = getattr(sys, 'tracebacklimit', 1000) n = 0 while frame is not None and n < limit: item = cls.callpoint_type.from_frame(frame) ret.append(item) frame = frame.f_back n += 1 ret.reverse() return cls(ret)
[docs] @classmethod def from_traceback(cls, tb=None, limit=None): """Create a new TracebackInfo from the traceback *tb* by recurring up in the stack a max of *limit* times. If *tb* is unset, get the traceback from the currently handled exception. If no exception is being handled, raise a :exc:`ValueError`. Args: frame (types.TracebackType): traceback object from :func:`sys.exc_info` or elsewhere. If absent or set to ``None``, defaults to ``sys.exc_info()[2]``, and raises a :exc:`ValueError` if no exception is currently being handled. limit (int): max number of parent frames to extract (defaults to :data:`sys.tracebacklimit`) """ ret = [] if tb is None: tb = sys.exc_info()[2] if tb is None: raise ValueError('no tb set and no exception being handled') if limit is None: limit = getattr(sys, 'tracebacklimit', 1000) n = 0 while tb is not None and n < limit: item = cls.callpoint_type.from_tb(tb) ret.append(item) tb = tb.tb_next n += 1 return cls(ret)
[docs] @classmethod def from_dict(cls, d): "Complements :meth:`TracebackInfo.to_dict`." # TODO: check this. return cls(d['frames'])
[docs] def to_dict(self): """Returns a dict with a list of :class:`Callpoint` frames converted to dicts. """ return {'frames': [f.to_dict() for f in self.frames]}
def __len__(self): return len(self.frames) def __iter__(self): return iter(self.frames) def __repr__(self): cn = self.__class__.__name__ if self.frames: frame_part = ' last=%r' % (self.frames[-1],) else: frame_part = '' return '<%s frames=%s%s>' % (cn, len(self.frames), frame_part) def __str__(self): return self.get_formatted()
[docs] def get_formatted(self): """Returns a string as formatted in the traditional Python built-in style observable when an exception is not caught. In other words, mimics :func:`traceback.format_tb` and :func:`traceback.format_stack`. """ ret = 'Traceback (most recent call last):\n' ret += ''.join([f.tb_frame_str() for f in self.frames]) return ret
[docs]class ExceptionInfo(object): """An ExceptionInfo object ties together three main fields suitable for representing an instance of an exception: The exception type name, a string representation of the exception itself (the exception message), and information about the traceback (stored as a :class:`TracebackInfo` object). These fields line up with :func:`sys.exc_info`, but unlike the values returned by that function, ExceptionInfo does not hold any references to the real exception or traceback. This property makes it suitable for serialization or long-term retention, without worrying about formatting pitfalls, circular references, or leaking memory. Args: exc_type (str): The exception type name. exc_msg (str): String representation of the exception value. tb_info (TracebackInfo): Information about the stack trace of the exception. Like the :class:`TracebackInfo`, ExceptionInfo is most commonly instantiated from one of its classmethods: :meth:`from_exc_info` or :meth:`from_current`. """ #: Override this in inherited types to control the TracebackInfo type used tb_info_type = TracebackInfo def __init__(self, exc_type, exc_msg, tb_info): # TODO: additional fields for SyntaxErrors self.exc_type = exc_type self.exc_msg = exc_msg self.tb_info = tb_info
[docs] @classmethod def from_exc_info(cls, exc_type, exc_value, traceback): """Create an :class:`ExceptionInfo` object from the exception's type, value, and traceback, as returned by :func:`sys.exc_info`. See also :meth:`from_current`. """ type_str = exc_type.__name__ type_mod = exc_type.__module__ if type_mod not in ("__main__", "__builtin__", "exceptions", "builtins"): type_str = '%s.%s' % (type_mod, type_str) val_str = _some_str(exc_value) tb_info = cls.tb_info_type.from_traceback(traceback) return cls(type_str, val_str, tb_info)
[docs] @classmethod def from_current(cls): """Create an :class:`ExceptionInfo` object from the current exception being handled, by way of :func:`sys.exc_info`. Will raise an exception if no exception is currently being handled. """ return cls.from_exc_info(*sys.exc_info())
[docs] def to_dict(self): """Get a :class:`dict` representation of the ExceptionInfo, suitable for JSON serialization. """ return {'exc_type': self.exc_type, 'exc_msg': self.exc_msg, 'exc_tb': self.tb_info.to_dict()}
def __repr__(self): cn = self.__class__.__name__ try: len_frames = len(self.tb_info.frames) last_frame = ', last=%r' % (self.tb_info.frames[-1],) except Exception: len_frames = 0 last_frame = '' args = (cn, self.exc_type, self.exc_msg, len_frames, last_frame) return '<%s [%s: %s] (%s frames%s)>' % args
[docs] def get_formatted(self): """Returns a string formatted in the traditional Python built-in style observable when an exception is not caught. In other words, mimics :func:`traceback.format_exception`. """ # TODO: add SyntaxError formatting tb_str = self.tb_info.get_formatted() return ''.join([tb_str, '%s: %s' % (self.exc_type, self.exc_msg)])
def get_formatted_exception_only(self): return '%s: %s' % (self.exc_type, self.exc_msg)
[docs]class ContextualCallpoint(Callpoint): """The ContextualCallpoint is a :class:`Callpoint` subtype with the exact same API and storing two additional values: 1. :func:`repr` outputs for local variables from the Callpoint's scope 2. A number of lines before and after the Callpoint's line of code The ContextualCallpoint is used by the :class:`ContextualTracebackInfo`. """ def __init__(self, *a, **kw): self.local_reprs = kw.pop('local_reprs', {}) self.pre_lines = kw.pop('pre_lines', []) self.post_lines = kw.pop('post_lines', []) super(ContextualCallpoint, self).__init__(*a, **kw)
[docs] @classmethod def from_frame(cls, frame): "Identical to :meth:`Callpoint.from_frame`" ret = super(ContextualCallpoint, cls).from_frame(frame) ret._populate_local_reprs(frame.f_locals) ret._populate_context_lines() return ret
[docs] @classmethod def from_tb(cls, tb): "Identical to :meth:`Callpoint.from_tb`" ret = super(ContextualCallpoint, cls).from_tb(tb) ret._populate_local_reprs(tb.tb_frame.f_locals) ret._populate_context_lines() return ret
def _populate_context_lines(self, pivot=8): DL, lineno = _DeferredLine, self.lineno try: module_globals = self.line.module_globals except Exception: module_globals = None start_line = max(0, lineno - pivot) pre_lines = [DL(self.module_path, ln, module_globals) for ln in range(start_line, lineno)] self.pre_lines[:] = pre_lines post_lines = [DL(self.module_path, ln, module_globals) for ln in range(lineno + 1, lineno + 1 + pivot)] self.post_lines[:] = post_lines return def _populate_local_reprs(self, f_locals): local_reprs = self.local_reprs for k, v in f_locals.items(): try: local_reprs[k] = repr(v) except Exception: surrogate = '<unprintable %s object>' % type(v).__name__ local_reprs[k] = surrogate return
[docs] def to_dict(self): """ Same principle as :meth:`Callpoint.to_dict`, but with the added contextual values. With ``ContextualCallpoint.to_dict()``, each frame will now be represented like:: {'func_name': 'print_example', 'lineno': 0, 'module_name': 'example_module', 'module_path': '/home/example/example_module.pyc', 'lasti': 0, 'line': 'print "example"', 'locals': {'variable': '"value"'}, 'pre_lines': ['variable = "value"'], 'post_lines': []} The locals dictionary and line lists are copies and can be mutated freely. """ ret = super(ContextualCallpoint, self).to_dict() ret['locals'] = dict(self.local_reprs) # get the line numbers and textual lines # without assuming DeferredLines start_line = self.lineno - len(self.pre_lines) pre_lines = [{'lineno': start_line + i, 'line': str(l)} for i, l in enumerate(self.pre_lines)] # trim off leading empty lines for i, item in enumerate(pre_lines): if item['line']: break if i: pre_lines = pre_lines[i:] ret['pre_lines'] = pre_lines # now post_lines post_lines = [{'lineno': self.lineno + i, 'line': str(l)} for i, l in enumerate(self.post_lines)] _last = 0 for i, item in enumerate(post_lines): if item['line']: _last = i post_lines = post_lines[:_last + 1] ret['post_lines'] = post_lines return ret
[docs]class ContextualTracebackInfo(TracebackInfo): """The ContextualTracebackInfo type is a :class:`TracebackInfo` subtype that is used by :class:`ContextualExceptionInfo` and uses the :class:`ContextualCallpoint` as its frame-representing primitive. """ callpoint_type = ContextualCallpoint
[docs]class ContextualExceptionInfo(ExceptionInfo): """The ContextualTracebackInfo type is a :class:`TracebackInfo` subtype that uses the :class:`ContextualCallpoint` as its frame-representing primitive. It carries with it most of the exception information required to recreate the widely recognizable "500" page for debugging Django applications. """ tb_info_type = ContextualTracebackInfo
# TODO: clean up & reimplement -- specifically for syntax errors def format_exception_only(etype, value): """Format the exception part of a traceback. The arguments are the exception type and value such as given by sys.last_type and sys.last_value. The return value is a list of strings, each ending in a newline. Normally, the list contains a single string; however, for SyntaxError exceptions, it contains several lines that (when printed) display detailed information about where the syntax error occurred. The message indicating which exception occurred is always the last string in the list. """ # Gracefully handle (the way Python 2.4 and earlier did) the case of # being called with (None, None). if etype is None: return [_format_final_exc_line(etype, value)] stype = etype.__name__ smod = etype.__module__ if smod not in ("__main__", "builtins", "exceptions"): stype = smod + '.' + stype if not issubclass(etype, SyntaxError): return [_format_final_exc_line(stype, value)] # It was a syntax error; show exactly where the problem was found. lines = [] filename = value.filename or "<string>" lineno = str(value.lineno) or '?' lines.append(' File "%s", line %s\n' % (filename, lineno)) badline = value.text offset = value.offset if badline is not None: lines.append(' %s\n' % badline.strip()) if offset is not None: caretspace = badline.rstrip('\n')[:offset].lstrip() # non-space whitespace (likes tabs) must be kept for alignment caretspace = ((c.isspace() and c or ' ') for c in caretspace) # only three spaces to account for offset1 == pos 0 lines.append(' %s^\n' % ''.join(caretspace)) msg = value.msg or "<no detail available>" lines.append("%s: %s\n" % (stype, msg)) return lines # TODO: use asciify, improved if necessary def _some_str(value): try: return str(value) except Exception: pass try: value = text(value) return value.encode("ascii", "backslashreplace") except Exception: pass return '<unprintable %s object>' % type(value).__name__ def _format_final_exc_line(etype, value): valuestr = _some_str(value) if value is None or not valuestr: line = "%s\n" % etype else: line = "%s: %s\n" % (etype, valuestr) return line def fix_print_exception(): """ Sets the default exception hook :func:`sys.excepthook` to the :func:`tbutils.print_exception` that uses all the ``tbutils`` facilities to provide slightly more correct output behavior. """ sys.excepthook = print_exception _frame_re = re.compile(r'^File "(?P<filepath>.+)", line (?P<lineno>\d+)' r', in (?P<funcname>.+)$') _se_frame_re = re.compile(r'^File "(?P<filepath>.+)", line (?P<lineno>\d+)') # TODO: ParsedException generator over large bodies of text
[docs]class ParsedException(object): """Stores a parsed traceback and exception as would be typically output by :func:`sys.excepthook` or :func:`traceback.print_exception`. .. note: Does not currently store SyntaxError details such as column. """ def __init__(self, exc_type_name, exc_msg, frames=None): self.exc_type = exc_type_name self.exc_msg = exc_msg self.frames = list(frames or []) @property def source_file(self): """ The file path of module containing the function that raised the exception, or None if not available. """ try: return self.frames[-1]['filepath'] except IndexError: return None
[docs] def to_dict(self): "Get a copy as a JSON-serializable :class:`dict`." return {'exc_type': self.exc_type, 'exc_msg': self.exc_msg, 'frames': list(self.frames)}
def __repr__(self): cn = self.__class__.__name__ return ('%s(%r, %r, frames=%r)' % (cn, self.exc_type, self.exc_msg, self.frames))
[docs] def to_string(self): """Formats the exception and its traceback into the standard format, as returned by the traceback module. ``ParsedException.from_string(text).to_string()`` should yield ``text``. """ lines = [u'Traceback (most recent call last):'] for frame in self.frames: lines.append(u' File "%s", line %s, in %s' % (frame['filepath'], frame['lineno'], frame['funcname'])) source_line = frame.get('source_line') if source_line: lines.append(u' %s' % (source_line,)) if self.exc_msg: lines.append(u'%s: %s' % (self.exc_type, self.exc_msg)) else: lines.append(u'%s' % (self.exc_type,)) return u'\n'.join(lines)
[docs] @classmethod def from_string(cls, tb_str): """Parse a traceback and exception from the text *tb_str*. This text is expected to have been decoded, otherwise it will be interpreted as UTF-8. This method does not search a larger body of text for tracebacks. If the first line of the text passed does not match one of the known patterns, a :exc:`ValueError` will be raised. This method will ignore trailing text after the end of the first traceback. Args: tb_str (str): The traceback text (:class:`unicode` or UTF-8 bytes) """ if not isinstance(tb_str, text): tb_str = tb_str.decode('utf-8') tb_lines = tb_str.lstrip().splitlines() # First off, handle some ignored exceptions. These can be the # result of exceptions raised by __del__ during garbage # collection while tb_lines: cl = tb_lines[-1] if cl.startswith('Exception ') and cl.endswith('ignored'): tb_lines.pop() else: break if tb_lines and tb_lines[0].strip() == 'Traceback (most recent call last):': start_line = 1 frame_re = _frame_re elif len(tb_lines) > 1 and tb_lines[-2].lstrip().startswith('^'): # This is to handle the slight formatting difference # associated with SyntaxErrors, which also don't really # have tracebacks start_line = 0 frame_re = _se_frame_re else: raise ValueError('unrecognized traceback string format') frames = [] line_no = start_line while True: frame_line = tb_lines[line_no].strip() frame_match = frame_re.match(frame_line) if frame_match: frame_dict = frame_match.groupdict() try: next_line = tb_lines[line_no + 1] except IndexError: # We read what we could next_line = '' next_line_stripped = next_line.strip() if ( frame_re.match(next_line_stripped) or # The exception message will not be indented # This check is to avoid overrunning on eval-like # tracebacks where the last frame doesn't have source # code in the traceback not next_line.startswith(' ') ): frame_dict['source_line'] = '' else: frame_dict['source_line'] = next_line_stripped line_no += 1 else: break line_no += 1 frames.append(frame_dict) try: exc_line = '\n'.join(tb_lines[line_no:]) exc_type, _, exc_msg = exc_line.partition(': ') except Exception: exc_type, exc_msg = '', '' return cls(exc_type, exc_msg, frames)
ParsedTB = ParsedException # legacy alias