cpython/Lib/traceback.py at 3.5 · python/cpython · GitHub

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"""Extract, format and print information about Python stack traces."""

import collections

import itertools

import linecache

import sys

__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', 'clear_frames',

'FrameSummary', 'StackSummary', 'TracebackException',

'walk_stack', 'walk_tb']

# Formatting and printing lists of traceback lines.

def print_list(extracted_list, file=None):

"""Print the list of tuples as returned by extract_tb() or

extract_stack() as a formatted stack trace to the given file."""

if file is None:

file = sys.stderr

for item in StackSummary.from_list(extracted_list).format():

print(item, file=file, end="")

def format_list(extracted_list):

"""Format a list of traceback entry tuples for printing.

Given a list of tuples as returned by extract_tb() or

extract_stack(), return a list of strings ready for printing.

Each string in the resulting list corresponds to the item with the

same index in the argument list. Each string ends in a newline;

the strings may contain internal newlines as well, for those items

whose source text line is not None.

"""

return StackSummary.from_list(extracted_list).format()

# Printing and Extracting Tracebacks.

def print_tb(tb, limit=None, file=None):

"""Print up to 'limit' stack trace entries from the traceback 'tb'.

If 'limit' is omitted or None, all entries are printed. If 'file'

is omitted or None, the output goes to sys.stderr; otherwise

'file' should be an open file or file-like object with a write()

method.

"""

print_list(extract_tb(tb, limit=limit), file=file)

def format_tb(tb, limit=None):

"""A shorthand for 'format_list(extract_tb(tb, limit))'."""

return extract_tb(tb, limit=limit).format()

def extract_tb(tb, limit=None):

"""Return list of up to limit pre-processed entries from traceback.

This is useful for alternate formatting of stack traces. If

'limit' is omitted or None, all entries are extracted. A

pre-processed stack trace entry is a quadruple (filename, line

number, function name, text) representing the information that is

usually printed for a stack trace. The text is a string with

leading and trailing whitespace stripped; if the source is not

available it is None.

"""

return StackSummary.extract(walk_tb(tb), limit=limit)

# Exception formatting and output.

_cause_message = (

"\nThe above exception was the direct cause "

"of the following exception:\n\n")

_context_message = (

"\nDuring handling of the above exception, "

"another exception occurred:\n\n")

def print_exception(etype, value, tb, limit=None, file=None, chain=True):

"""Print exception up to 'limit' stack trace entries from 'tb' to 'file'.

This differs from print_tb() in the following ways: (1) if

traceback is not None, it prints a header "Traceback (most recent

call last):"; (2) it prints the exception type and value after the

stack trace; (3) if type is SyntaxError and value has the

appropriate format, it prints the line where the syntax error

occurred with a caret on the next line indicating the approximate

position of the error.

"""

# format_exception has ignored etype for some time, and code such as cgitb

# passes in bogus values as a result. For compatibility with such code we

# ignore it here (rather than in the new TracebackException API).

if file is None:

file = sys.stderr

for line in TracebackException(

type(value), value, tb, limit=limit).format(chain=chain):

print(line, file=file, end="")

def format_exception(etype, value, tb, limit=None, chain=True):

"""Format a stack trace and the exception information.

The arguments have the same meaning as the corresponding arguments

to print_exception(). The return value is a list of strings, each

ending in a newline and some containing internal newlines. When

these lines are concatenated and printed, exactly the same text is

printed as does print_exception().

"""

# format_exception has ignored etype for some time, and code such as cgitb

# passes in bogus values as a result. For compatibility with such code we

# ignore it here (rather than in the new TracebackException API).

return list(TracebackException(

type(value), value, tb, limit=limit).format(chain=chain))

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.

"""

return list(TracebackException(etype, value, None).format_exception_only())

# -- not official API but folk probably use these two functions.

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 _some_str(value):

try:

return str(value)

except:

return '<unprintable %s object>' % type(value).__name__

# --

def print_exc(limit=None, file=None, chain=True):

"""Shorthand for 'print_exception(*sys.exc_info(), limit, file)'."""

print_exception(*sys.exc_info(), limit=limit, file=file, chain=chain)

def format_exc(limit=None, chain=True):

"""Like print_exc() but return a string."""

return "".join(format_exception(*sys.exc_info(), limit=limit, chain=chain))

def print_last(limit=None, file=None, chain=True):

"""This is a shorthand for 'print_exception(sys.last_type,

sys.last_value, sys.last_traceback, limit, file)'."""

if not hasattr(sys, "last_type"):

raise ValueError("no last exception")

print_exception(sys.last_type, sys.last_value, sys.last_traceback,

limit, file, chain)

# Printing and Extracting Stacks.

def print_stack(f=None, limit=None, file=None):

"""Print a stack trace from its invocation point.

The optional 'f' argument can be used to specify an alternate

stack frame at which to start. The optional 'limit' and 'file'

arguments have the same meaning as for print_exception().

"""

if f is None:

f = sys._getframe().f_back

print_list(extract_stack(f, limit=limit), file=file)

def format_stack(f=None, limit=None):

"""Shorthand for 'format_list(extract_stack(f, limit))'."""

if f is None:

f = sys._getframe().f_back

return format_list(extract_stack(f, limit=limit))

def extract_stack(f=None, limit=None):

"""Extract the raw traceback from the current stack frame.

The return value has the same format as for extract_tb(). The

optional 'f' and 'limit' arguments have the same meaning as for

print_stack(). Each item in the list is a quadruple (filename,

line number, function name, text), and the entries are in order

from oldest to newest stack frame.

"""

if f is None:

f = sys._getframe().f_back

stack = StackSummary.extract(walk_stack(f), limit=limit)

stack.reverse()

return stack

def clear_frames(tb):

"Clear all references to local variables in the frames of a traceback."

while tb is not None:

try:

tb.tb_frame.clear()

except RuntimeError:

# Ignore the exception raised if the frame is still executing.

pass

tb = tb.tb_next

class FrameSummary:

"""A single frame from a traceback.

- :attr:`filename` The filename for the frame.

- :attr:`lineno` The line within filename for the frame that was

active when the frame was captured.

- :attr:`name` The name of the function or method that was executing

when the frame was captured.

- :attr:`line` The text from the linecache module for the

of code that was running when the frame was captured.

- :attr:`locals` Either None if locals were not supplied, or a dict

mapping the name to the repr() of the variable.

"""

__slots__ = ('filename', 'lineno', 'name', '_line', 'locals')

def __init__(self, filename, lineno, name, *, lookup_line=True,

locals=None, line=None):

"""Construct a FrameSummary.

:param lookup_line: If True, `linecache` is consulted for the source

code line. Otherwise, the line will be looked up when first needed.

:param locals: If supplied the frame locals, which will be captured as

object representations.

:param line: If provided, use this instead of looking up the line in

the linecache.

"""

self.filename = filename

self.lineno = lineno

self.name = name

self._line = line

if lookup_line:

self.line

self.locals = \

dict((k, repr(v)) for k, v in locals.items()) if locals else None

def __eq__(self, other):

if isinstance(other, FrameSummary):

return (self.filename == other.filename and

self.lineno == other.lineno and

self.name == other.name and

self.locals == other.locals)

if isinstance(other, tuple):

return (self.filename, self.lineno, self.name, self.line) == other

return NotImplemented

def __getitem__(self, pos):

return (self.filename, self.lineno, self.name, self.line)[pos]

def __iter__(self):

return iter([self.filename, self.lineno, self.name, self.line])

def __repr__(self):

return "<FrameSummary file {filename}, line {lineno} in {name}>".format(

filename=self.filename, lineno=self.lineno, name=self.name)

@property

def line(self):

if self._line is None:

self._line = linecache.getline(self.filename, self.lineno).strip()

return self._line

def walk_stack(f):

"""Walk a stack yielding the frame and line number for each frame.

This will follow f.f_back from the given frame. If no frame is given, the

current stack is used. Usually used with StackSummary.extract.

"""

if f is None:

f = sys._getframe().f_back.f_back

while f is not None:

yield f, f.f_lineno

f = f.f_back

def walk_tb(tb):

"""Walk a traceback yielding the frame and line number for each frame.

This will follow tb.tb_next (and thus is in the opposite order to

walk_stack). Usually used with StackSummary.extract.

"""

while tb is not None:

yield tb.tb_frame, tb.tb_lineno

tb = tb.tb_next

class StackSummary(list):

"""A stack of frames."""

@classmethod

def extract(klass, frame_gen, *, limit=None, lookup_lines=True,

capture_locals=False):

"""Create a StackSummary from a traceback or stack object.

:param frame_gen: A generator that yields (frame, lineno) tuples to

include in the stack.

:param limit: None to include all frames or the number of frames to

include.

:param lookup_lines: If True, lookup lines for each frame immediately,

otherwise lookup is deferred until the frame is rendered.

:param capture_locals: If True, the local variables from each frame will

be captured as object representations into the FrameSummary.

"""

if limit is None:

limit = getattr(sys, 'tracebacklimit', None)

if limit is not None and limit < 0:

limit = 0

if limit is not None:

if limit >= 0:

frame_gen = itertools.islice(frame_gen, limit)

else:

frame_gen = collections.deque(frame_gen, maxlen=-limit)

result = klass()

fnames = set()

for f, lineno in frame_gen:

co = f.f_code

filename = co.co_filename

name = co.co_name

fnames.add(filename)

linecache.lazycache(filename, f.f_globals)

# Must defer line lookups until we have called checkcache.

if capture_locals:

f_locals = f.f_locals

else:

f_locals = None

result.append(FrameSummary(

filename, lineno, name, lookup_line=False, locals=f_locals))

for filename in fnames:

linecache.checkcache(filename)

# If immediate lookup was desired, trigger lookups now.

if lookup_lines:

for f in result:

f.line

return result

@classmethod

def from_list(klass, a_list):

"""Create a StackSummary from a simple list of tuples.

This method supports the older Python API. Each tuple should be a

4-tuple with (filename, lineno, name, line) elements.

"""

# While doing a fast-path check for isinstance(a_list, StackSummary) is

# appealing, idlelib.run.cleanup_traceback and other similar code may

# break this by making arbitrary frames plain tuples, so we need to

# check on a frame by frame basis.

result = StackSummary()

for frame in a_list:

if isinstance(frame, FrameSummary):

result.append(frame)

else:

filename, lineno, name, line = frame

result.append(FrameSummary(filename, lineno, name, line=line))

return result

def format(self):

"""Format the stack ready for printing.

Returns a list of strings ready for printing. Each string in the

resulting list corresponds to a single frame from the stack.

Each string ends in a newline; the strings may contain internal

newlines as well, for those items with source text lines.

"""

result = []

for frame in self:

row = []

row.append(' File "{}", line {}, in {}\n'.format(

frame.filename, frame.lineno, frame.name))

if frame.line:

row.append(' {}\n'.format(frame.line.strip()))

if frame.locals:

for name, value in sorted(frame.locals.items()):

row.append(' {name} = {value}\n'.format(name=name, value=value))

result.append(''.join(row))

return result

class TracebackException:

"""An exception ready for rendering.

The traceback module captures enough attributes from the original exception

to this intermediary form to ensure that no references are held, while

still being able to fully print or format it.

Use `from_exception` to create TracebackException instances from exception

objects, or the constructor to create TracebackException instances from

individual components.

- :attr:`__cause__` A TracebackException of the original *__cause__*.

- :attr:`__context__` A TracebackException of the original *__context__*.

- :attr:`__suppress_context__` The *__suppress_context__* value from the

original exception.

- :attr:`stack` A `StackSummary` representing the traceback.

- :attr:`exc_type` The class of the original traceback.

- :attr:`filename` For syntax errors - the filename where the error

occurred.

- :attr:`lineno` For syntax errors - the linenumber where the error

occurred.

- :attr:`text` For syntax errors - the text where the error

occurred.

- :attr:`offset` For syntax errors - the offset into the text where the

error occurred.

- :attr:`msg` For syntax errors - the compiler error message.

"""

def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,

lookup_lines=True, capture_locals=False, _seen=None):

# NB: we need to accept exc_traceback, exc_value, exc_traceback to

# permit backwards compat with the existing API, otherwise we

# need stub thunk objects just to glue it together.

# Handle loops in __cause__ or __context__.

if _seen is None:

_seen = set()

_seen.add(exc_value)

# Gracefully handle (the way Python 2.4 and earlier did) the case of

# being called with no type or value (None, None, None).

if (exc_value and exc_value.__cause__ is not None

and exc_value.__cause__ not in _seen):

cause = TracebackException(

type(exc_value.__cause__),

exc_value.__cause__,

exc_value.__cause__.__traceback__,

limit=limit,

lookup_lines=False,

capture_locals=capture_locals,

_seen=_seen)

else:

cause = None

if (exc_value and exc_value.__context__ is not None

and exc_value.__context__ not in _seen):

context = TracebackException(

type(exc_value.__context__),

exc_value.__context__,

exc_value.__context__.__traceback__,

limit=limit,

lookup_lines=False,

capture_locals=capture_locals,

_seen=_seen)

else:

context = None

self.exc_traceback = exc_traceback

self.__cause__ = cause

self.__context__ = context

self.__suppress_context__ = \

exc_value.__suppress_context__ if exc_value else False

# TODO: locals.

self.stack = StackSummary.extract(

walk_tb(exc_traceback), limit=limit, lookup_lines=lookup_lines,

capture_locals=capture_locals)

self.exc_type = exc_type

# Capture now to permit freeing resources: only complication is in the

# unofficial API _format_final_exc_line

self._str = _some_str(exc_value)

if exc_type and issubclass(exc_type, SyntaxError):

# Handle SyntaxError's specially

self.filename = exc_value.filename

self.lineno = str(exc_value.lineno)

self.text = exc_value.text

self.offset = exc_value.offset

self.msg = exc_value.msg

if lookup_lines:

self._load_lines()

@classmethod

def from_exception(self, exc, *args, **kwargs):

"""Create a TracebackException from an exception."""

return TracebackException(

type(exc), exc, exc.__traceback__, *args, **kwargs)

def _load_lines(self):

"""Private API. force all lines in the stack to be loaded."""

for frame in self.stack:

frame.line

if self.__context__:

self.__context__._load_lines()

if self.__cause__:

self.__cause__._load_lines()

def __eq__(self, other):

return self.__dict__ == other.__dict__

def __str__(self):

return self._str

def format_exception_only(self):

"""Format the exception part of the traceback.

The return value is a generator of strings, each ending in a newline.

Normally, the generator emits a single string; however, for

SyntaxError exceptions, it emites 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 output.

"""

if self.exc_type is None:

yield _format_final_exc_line(None, self._str)

return

stype = self.exc_type.__qualname__

smod = self.exc_type.__module__

if smod not in ("__main__", "builtins"):

stype = smod + '.' + stype

if not issubclass(self.exc_type, SyntaxError):

yield _format_final_exc_line(stype, self._str)

return

# It was a syntax error; show exactly where the problem was found.

filename = self.filename or "<string>"

lineno = str(self.lineno) or '?'

yield ' File "{}", line {}\n'.format(filename, lineno)

badline = self.text

offset = self.offset

if badline is not None:

yield ' {}\n'.format(badline.strip())

if offset is not None:

caretspace = badline.rstrip('\n')

offset = min(len(caretspace), offset) - 1

caretspace = caretspace[:offset].lstrip()

# non-space whitespace (likes tabs) must be kept for alignment

caretspace = ((c.isspace() and c or ' ') for c in caretspace)

yield ' {}^\n'.format(''.join(caretspace))

msg = self.msg or "<no detail available>"

yield "{}: {}\n".format(stype, msg)

def format(self, *, chain=True):

"""Format the exception.

If chain is not *True*, *__cause__* and *__context__* will not be formatted.

The return value is a generator of strings, each ending in a newline and

some containing internal newlines. `print_exception` is a wrapper around

this method which just prints the lines to a file.

The message indicating which exception occurred is always the last

string in the output.

"""

if chain:

if self.__cause__ is not None:

yield from self.__cause__.format(chain=chain)

yield _cause_message

elif (self.__context__ is not None and

not self.__suppress_context__):

yield from self.__context__.format(chain=chain)

yield _context_message

if self.exc_traceback is not None:

yield 'Traceback (most recent call last):\n'

yield from self.stack.format()

yield from self.format_exception_only()

cpython/Lib/traceback.py at 3.5 · python/cpython · GitHub

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