Issue #17911: traceback module overhaul

Provide a way to seed the linecache for a PEP-302 module without actually
loading the code.

Provide a new object API for traceback, including the ability to not lookup
lines at all until the traceback is actually rendered, without any trace of the
original objects being kept alive.
This commit is contained in:
Robert Collins 2015-03-05 12:07:57 +13:00
parent 0bfd0a4048
commit 6bc2c1e7eb
7 changed files with 791 additions and 154 deletions

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@ -43,6 +43,14 @@ The :mod:`linecache` module defines the following functions:
changed on disk, and you require the updated version. If *filename* is omitted,
it will check all the entries in the cache.
.. function:: lazycache(filename, module_globals)
Capture enough detail about a non-file based module to permit getting its
lines later via :func:`getline` even if *module_globals* is None in the later
call. This avoids doing I/O until a line is actually needed, without having
to carry the module globals around indefinitely.
.. versionadded:: 3.5
Example::

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@ -136,6 +136,130 @@ The module defines the following functions:
.. versionadded:: 3.4
.. function:: walk_stack(f)
Walk a stack following f.f_back from the given frame, yielding the frame and
line number for each frame. If f is None, the current stack is used.
This helper is used with *Stack.extract*.
.. versionadded:: 3.5
.. function:: walk_tb(tb)
Walk a traceback following tb_next yielding the frame and line number for
each frame. This helper is used with *Stack.extract*.
.. versionadded:: 3.5
The module also defines the following classes:
:class:`TracebackException` Objects
-----------------------------------
:class:`.TracebackException` objects are created from actual exceptions to
capture data for later printing in a lightweight fashion.
.. class:: TracebackException(exc_type, exc_value, exc_traceback, limit=None, lookup_lines=True)
Capture an exception for later rendering. limit, lookup_lines are as for
the :class:`.StackSummary` class.
.. versionadded:: 3.5
.. classmethod:: `.from_exception`(exc, limit=None, lookup_lines=True)
Capture an exception for later rendering. limit and lookup_lines
are as for the :class:`.StackSummary` class.
.. versionadded:: 3.5
.. attribute:: `.__cause__` A TracebackException of the original *__cause__*.
.. attribute:: `.__context__` A TracebackException of the original *__context__*.
.. attribute:: `.__suppress_context__` The *__suppress_context__* value from the
original exception.
.. attribute:: `.stack` A `StackSummary` representing the traceback.
.. attribute:: `.exc_type` The class of the original traceback.
.. attribute:: `.filename` For syntax errors - the filename where the error
occured.
.. attribute:: `.lineno` For syntax errors - the linenumber where the error
occured.
.. attribute:: `.text` For syntax errors - the text where the error
occured.
.. attribute:: `.offset` For syntax errors - the offset into the text where the
error occured.
.. attribute:: `.msg` For syntax errors - the compiler error message.
.. method:: TracebackException.format(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.
.. versionadded:: 3.5
.. method:: TracebackException.format_exception_only()
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.
.. versionadded:: 3.5
:class:`StackSummary` Objects
-----------------------------
:class:`.StackSummary` objects represent a call stack ready for formatting.
.. classmethod:: StackSummary.extract(frame_gen, limit=None, lookup_lines=True)
Construct a StackSummary object from a frame generator (such as is returned by
`walk_stack` or `walk_tb`.
If limit is supplied, only this many frames are taken from frame_gen.
If lookup_lines is False, the returned FrameSummary objects will not have read
their lines in yet, making the cost of creating the StackSummary cheaper (which
may be valuable if it may not actually get formatted).
.. versionadded:: 3.5
.. classmethod:: StackSummary.from_list(a_list)
Construct a StackSummary object from a supplied old-style list of tuples. Each
tuple should be a 4-tuple with filename, lineno, name, line as the elements.
.. versionadded:: 3.5
:class:`FrameSummary` Objects
-----------------------------
FrameSummary objects represent a single frame in a traceback.
.. class:: FrameSummary(filename, lineno, name, lookup_line=True, locals=None, line=None)
:noindex:
Represent a single frame in the traceback or stack that is being formatted
or printed. It may optionally have a stringified version of the frames
locals included in it. If *lookup_line* is False, the source code is not
looked up until the FrameSummary has the :attr:`line` attribute accessed (which
also happens when casting it to a tuple). Line may be directly provided, and
will prevent line lookups happening at all.
.. _traceback-example:

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@ -5,6 +5,7 @@ is not found, it will look down the module search path for a file by
that name.
"""
import functools
import sys
import os
import tokenize
@ -21,7 +22,9 @@ def getline(filename, lineno, module_globals=None):
# The cache
cache = {} # The cache
# The cache. Maps filenames to either a thunk which will provide source code,
# or a tuple (size, mtime, lines, fullname) once loaded.
cache = {}
def clearcache():
@ -36,6 +39,9 @@ def getlines(filename, module_globals=None):
Update the cache if it doesn't contain an entry for this file already."""
if filename in cache:
entry = cache[filename]
if len(entry) == 1:
return updatecache(filename, module_globals)
return cache[filename][2]
else:
return updatecache(filename, module_globals)
@ -54,7 +60,11 @@ def checkcache(filename=None):
return
for filename in filenames:
size, mtime, lines, fullname = cache[filename]
entry = cache[filename]
if len(entry) == 1:
# lazy cache entry, leave it lazy.
continue
size, mtime, lines, fullname = entry
if mtime is None:
continue # no-op for files loaded via a __loader__
try:
@ -72,7 +82,8 @@ def updatecache(filename, module_globals=None):
and return an empty list."""
if filename in cache:
del cache[filename]
if len(cache[filename]) != 1:
del cache[filename]
if not filename or (filename.startswith('<') and filename.endswith('>')):
return []
@ -82,27 +93,23 @@ def updatecache(filename, module_globals=None):
except OSError:
basename = filename
# Try for a __loader__, if available
if module_globals and '__loader__' in module_globals:
name = module_globals.get('__name__')
loader = module_globals['__loader__']
get_source = getattr(loader, 'get_source', None)
if name and get_source:
try:
data = get_source(name)
except (ImportError, OSError):
pass
else:
if data is None:
# No luck, the PEP302 loader cannot find the source
# for this module.
return []
cache[filename] = (
len(data), None,
[line+'\n' for line in data.splitlines()], fullname
)
return cache[filename][2]
# Realise a lazy loader based lookup if there is one
# otherwise try to lookup right now.
if lazycache(filename, module_globals):
try:
data = cache[filename][0]()
except (ImportError, OSError):
pass
else:
if data is None:
# No luck, the PEP302 loader cannot find the source
# for this module.
return []
cache[filename] = (
len(data), None,
[line+'\n' for line in data.splitlines()], fullname
)
return cache[filename][2]
# Try looking through the module search path, which is only useful
# when handling a relative filename.
@ -132,3 +139,36 @@ def updatecache(filename, module_globals=None):
size, mtime = stat.st_size, stat.st_mtime
cache[filename] = size, mtime, lines, fullname
return lines
def lazycache(filename, module_globals):
"""Seed the cache for filename with module_globals.
The module loader will be asked for the source only when getlines is
called, not immediately.
If there is an entry in the cache already, it is not altered.
:return: True if a lazy load is registered in the cache,
otherwise False. To register such a load a module loader with a
get_source method must be found, the filename must be a cachable
filename, and the filename must not be already cached.
"""
if filename in cache:
if len(cache[filename]) == 1:
return True
else:
return False
if not filename or (filename.startswith('<') and filename.endswith('>')):
return False
# Try for a __loader__, if available
if module_globals and '__loader__' in module_globals:
name = module_globals.get('__name__')
loader = module_globals['__loader__']
get_source = getattr(loader, 'get_source', None)
if name and get_source:
get_lines = functools.partial(get_source, name)
cache[filename] = (get_lines,)
return True
return False

View File

@ -7,6 +7,7 @@ from test import support
FILENAME = linecache.__file__
NONEXISTENT_FILENAME = FILENAME + '.missing'
INVALID_NAME = '!@$)(!@#_1'
EMPTY = ''
TESTS = 'inspect_fodder inspect_fodder2 mapping_tests'
@ -126,6 +127,49 @@ class LineCacheTests(unittest.TestCase):
self.assertEqual(line, getline(source_name, index + 1))
source_list.append(line)
def test_lazycache_no_globals(self):
lines = linecache.getlines(FILENAME)
linecache.clearcache()
self.assertEqual(False, linecache.lazycache(FILENAME, None))
self.assertEqual(lines, linecache.getlines(FILENAME))
def test_lazycache_smoke(self):
lines = linecache.getlines(NONEXISTENT_FILENAME, globals())
linecache.clearcache()
self.assertEqual(
True, linecache.lazycache(NONEXISTENT_FILENAME, globals()))
self.assertEqual(1, len(linecache.cache[NONEXISTENT_FILENAME]))
# Note here that we're looking up a non existant filename with no
# globals: this would error if the lazy value wasn't resolved.
self.assertEqual(lines, linecache.getlines(NONEXISTENT_FILENAME))
def test_lazycache_provide_after_failed_lookup(self):
linecache.clearcache()
lines = linecache.getlines(NONEXISTENT_FILENAME, globals())
linecache.clearcache()
linecache.getlines(NONEXISTENT_FILENAME)
linecache.lazycache(NONEXISTENT_FILENAME, globals())
self.assertEqual(lines, linecache.updatecache(NONEXISTENT_FILENAME))
def test_lazycache_check(self):
linecache.clearcache()
linecache.lazycache(NONEXISTENT_FILENAME, globals())
linecache.checkcache()
def test_lazycache_bad_filename(self):
linecache.clearcache()
self.assertEqual(False, linecache.lazycache('', globals()))
self.assertEqual(False, linecache.lazycache('<foo>', globals()))
def test_lazycache_already_cached(self):
linecache.clearcache()
lines = linecache.getlines(NONEXISTENT_FILENAME, globals())
self.assertEqual(
False,
linecache.lazycache(NONEXISTENT_FILENAME, globals()))
self.assertEqual(4, len(linecache.cache[NONEXISTENT_FILENAME]))
def test_main():
support.run_unittest(LineCacheTests)

View File

@ -1,6 +1,8 @@
"""Test cases for traceback module"""
from collections import namedtuple
from io import StringIO
import linecache
import sys
import unittest
import re
@ -12,6 +14,11 @@ import textwrap
import traceback
test_code = namedtuple('code', ['co_filename', 'co_name'])
test_frame = namedtuple('frame', ['f_code', 'f_globals'])
test_tb = namedtuple('tb', ['tb_frame', 'tb_lineno', 'tb_next'])
class SyntaxTracebackCases(unittest.TestCase):
# For now, a very minimal set of tests. I want to be sure that
# formatting of SyntaxErrors works based on changes for 2.1.
@ -477,6 +484,195 @@ class MiscTracebackCases(unittest.TestCase):
self.assertEqual(len(inner_frame.f_locals), 0)
class TestFrame(unittest.TestCase):
def test_basics(self):
linecache.clearcache()
linecache.lazycache("f", globals())
f = traceback.FrameSummary("f", 1, "dummy")
self.assertEqual(
("f", 1, "dummy", '"""Test cases for traceback module"""'),
tuple(f))
self.assertEqual(None, f.locals)
def test_lazy_lines(self):
linecache.clearcache()
f = traceback.FrameSummary("f", 1, "dummy", lookup_line=False)
self.assertEqual(None, f._line)
linecache.lazycache("f", globals())
self.assertEqual(
'"""Test cases for traceback module"""',
f.line)
def test_explicit_line(self):
f = traceback.FrameSummary("f", 1, "dummy", line="line")
self.assertEqual("line", f.line)
class TestStack(unittest.TestCase):
def test_walk_stack(self):
s = list(traceback.walk_stack(None))
self.assertGreater(len(s), 10)
def test_walk_tb(self):
try:
1/0
except Exception:
_, _, tb = sys.exc_info()
s = list(traceback.walk_tb(tb))
self.assertEqual(len(s), 1)
def test_extract_stack(self):
s = traceback.StackSummary.extract(traceback.walk_stack(None))
self.assertIsInstance(s, traceback.StackSummary)
def test_extract_stack_limit(self):
s = traceback.StackSummary.extract(traceback.walk_stack(None), limit=5)
self.assertEqual(len(s), 5)
def test_extract_stack_lookup_lines(self):
linecache.clearcache()
linecache.updatecache('/foo.py', globals())
c = test_code('/foo.py', 'method')
f = test_frame(c, None)
s = traceback.StackSummary.extract(iter([(f, 6)]), lookup_lines=True)
linecache.clearcache()
self.assertEqual(s[0].line, "import sys")
def test_extract_stackup_deferred_lookup_lines(self):
linecache.clearcache()
c = test_code('/foo.py', 'method')
f = test_frame(c, None)
s = traceback.StackSummary.extract(iter([(f, 6)]), lookup_lines=False)
self.assertEqual({}, linecache.cache)
linecache.updatecache('/foo.py', globals())
self.assertEqual(s[0].line, "import sys")
def test_from_list(self):
s = traceback.StackSummary([('foo.py', 1, 'fred', 'line')])
self.assertEqual(
[' File "foo.py", line 1, in fred\n line\n'],
s.format())
def test_format_smoke(self):
# For detailed tests see the format_list tests, which consume the same
# code.
s = traceback.StackSummary([('foo.py', 1, 'fred', 'line')])
self.assertEqual(
[' File "foo.py", line 1, in fred\n line\n'],
s.format())
class TestTracebackException(unittest.TestCase):
def test_smoke(self):
try:
1/0
except Exception:
exc_info = sys.exc_info()
exc = traceback.TracebackException(*exc_info)
expected_stack = traceback.StackSummary.extract(
traceback.walk_tb(exc_info[2]))
self.assertEqual(None, exc.__cause__)
self.assertEqual(None, exc.__context__)
self.assertEqual(False, exc.__suppress_context__)
self.assertEqual(expected_stack, exc.stack)
self.assertEqual(exc_info[0], exc.exc_type)
self.assertEqual(str(exc_info[1]), str(exc))
def test_from_exception(self):
# Check all the parameters are accepted.
def foo():
1/0
try:
foo()
except Exception as e:
exc_info = sys.exc_info()
self.expected_stack = traceback.StackSummary.extract(
traceback.walk_tb(exc_info[2]), limit=1, lookup_lines=False,
capture_locals=True)
self.exc = traceback.TracebackException.from_exception(
e, limit=1, lookup_lines=False, capture_locals=True)
expected_stack = self.expected_stack
exc = self.exc
self.assertEqual(None, exc.__cause__)
self.assertEqual(None, exc.__context__)
self.assertEqual(False, exc.__suppress_context__)
self.assertEqual(expected_stack, exc.stack)
self.assertEqual(exc_info[0], exc.exc_type)
self.assertEqual(str(exc_info[1]), str(exc))
def test_cause(self):
try:
try:
1/0
finally:
exc_info_context = sys.exc_info()
exc_context = traceback.TracebackException(*exc_info_context)
cause = Exception("cause")
raise Exception("uh oh") from cause
except Exception:
exc_info = sys.exc_info()
exc = traceback.TracebackException(*exc_info)
expected_stack = traceback.StackSummary.extract(
traceback.walk_tb(exc_info[2]))
exc_cause = traceback.TracebackException(Exception, cause, None)
self.assertEqual(exc_cause, exc.__cause__)
self.assertEqual(exc_context, exc.__context__)
self.assertEqual(True, exc.__suppress_context__)
self.assertEqual(expected_stack, exc.stack)
self.assertEqual(exc_info[0], exc.exc_type)
self.assertEqual(str(exc_info[1]), str(exc))
def test_context(self):
try:
try:
1/0
finally:
exc_info_context = sys.exc_info()
exc_context = traceback.TracebackException(*exc_info_context)
raise Exception("uh oh")
except Exception:
exc_info = sys.exc_info()
exc = traceback.TracebackException(*exc_info)
expected_stack = traceback.StackSummary.extract(
traceback.walk_tb(exc_info[2]))
self.assertEqual(None, exc.__cause__)
self.assertEqual(exc_context, exc.__context__)
self.assertEqual(False, exc.__suppress_context__)
self.assertEqual(expected_stack, exc.stack)
self.assertEqual(exc_info[0], exc.exc_type)
self.assertEqual(str(exc_info[1]), str(exc))
def test_limit(self):
def recurse(n):
if n:
recurse(n-1)
else:
1/0
try:
recurse(10)
except Exception:
exc_info = sys.exc_info()
exc = traceback.TracebackException(*exc_info, limit=5)
expected_stack = traceback.StackSummary.extract(
traceback.walk_tb(exc_info[2]), limit=5)
self.assertEqual(expected_stack, exc.stack)
def test_lookup_lines(self):
linecache.clearcache()
e = Exception("uh oh")
c = test_code('/foo.py', 'method')
f = test_frame(c, None)
tb = test_tb(f, 6, None)
exc = traceback.TracebackException(Exception, e, tb, lookup_lines=False)
self.assertEqual({}, linecache.cache)
linecache.updatecache('/foo.py', globals())
self.assertEqual(exc.stack[0].line, "import sys")
def test_main():
run_unittest(__name__)

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@ -14,19 +14,12 @@ __all__ = ['extract_stack', 'extract_tb', 'format_exception',
# Formatting and printing lists of traceback lines.
#
def _format_list_iter(extracted_list):
for filename, lineno, name, line in extracted_list:
item = ' File "{}", line {}, in {}\n'.format(filename, lineno, name)
if line:
item = item + ' {}\n'.format(line.strip())
yield item
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 _format_list_iter(extracted_list):
for item in StackSummary.from_list(extracted_list).format():
print(item, file=file, end="")
def format_list(extracted_list):
@ -39,45 +32,12 @@ def format_list(extracted_list):
the strings may contain internal newlines as well, for those items
whose source text line is not None.
"""
return list(_format_list_iter(extracted_list))
return StackSummary.from_list(extracted_list).format()
#
# Printing and Extracting Tracebacks.
#
# extractor takes curr and needs to return a tuple of:
# - Frame object
# - Line number
# - Next item (same type as curr)
# In practice, curr is either a traceback or a frame.
def _extract_tb_or_stack_iter(curr, limit, extractor):
if limit is None:
limit = getattr(sys, 'tracebacklimit', None)
n = 0
while curr is not None and (limit is None or n < limit):
f, lineno, next_item = extractor(curr)
co = f.f_code
filename = co.co_filename
name = co.co_name
linecache.checkcache(filename)
line = linecache.getline(filename, lineno, f.f_globals)
if line:
line = line.strip()
else:
line = None
yield (filename, lineno, name, line)
curr = next_item
n += 1
def _extract_tb_iter(tb, limit):
return _extract_tb_or_stack_iter(
tb, limit,
operator.attrgetter("tb_frame", "tb_lineno", "tb_next"))
def print_tb(tb, limit=None, file=None):
"""Print up to 'limit' stack trace entries from the traceback 'tb'.
@ -90,7 +50,7 @@ def print_tb(tb, limit=None, file=None):
def format_tb(tb, limit=None):
"""A shorthand for 'format_list(extract_tb(tb, limit))'."""
return format_list(extract_tb(tb, limit=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.
@ -103,7 +63,7 @@ def extract_tb(tb, limit=None):
leading and trailing whitespace stripped; if the source is not
available it is None.
"""
return list(_extract_tb_iter(tb, limit=limit))
return StackSummary.extract(walk_tb(tb), limit=limit)
#
# Exception formatting and output.
@ -111,47 +71,12 @@ def extract_tb(tb, limit=None):
_cause_message = (
"\nThe above exception was the direct cause "
"of the following exception:\n")
"of the following exception:\n\n")
_context_message = (
"\nDuring handling of the above exception, "
"another exception occurred:\n")
"another exception occurred:\n\n")
def _iter_chain(exc, custom_tb=None, seen=None):
if seen is None:
seen = set()
seen.add(exc)
its = []
context = exc.__context__
cause = exc.__cause__
if cause is not None and cause not in seen:
its.append(_iter_chain(cause, False, seen))
its.append([(_cause_message, None)])
elif (context is not None and
not exc.__suppress_context__ and
context not in seen):
its.append(_iter_chain(context, None, seen))
its.append([(_context_message, None)])
its.append([(exc, custom_tb or exc.__traceback__)])
# itertools.chain is in an extension module and may be unavailable
for it in its:
yield from it
def _format_exception_iter(etype, value, tb, limit, chain):
if chain:
values = _iter_chain(value, tb)
else:
values = [(value, tb)]
for value, tb in values:
if isinstance(value, str):
# This is a cause/context message line
yield value + '\n'
continue
if tb:
yield 'Traceback (most recent call last):\n'
yield from _format_list_iter(_extract_tb_iter(tb, limit=limit))
yield from _format_exception_only_iter(type(value), value)
def print_exception(etype, value, tb, limit=None, file=None, chain=True):
"""Print exception up to 'limit' stack trace entries from 'tb' to 'file'.
@ -166,9 +91,11 @@ def print_exception(etype, value, tb, limit=None, file=None, chain=True):
"""
if file is None:
file = sys.stderr
for line in _format_exception_iter(etype, value, tb, limit, chain):
for line in TracebackException(
etype, 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.
@ -178,7 +105,9 @@ def format_exception(etype, value, tb, limit=None, chain=True):
these lines are concatenated and printed, exactly the same text is
printed as does print_exception().
"""
return list(_format_exception_iter(etype, value, tb, limit, chain))
return list(TracebackException(
etype, value, tb, limit=limit).format(chain=chain))
def format_exception_only(etype, value):
"""Format the exception part of a traceback.
@ -196,46 +125,14 @@ def format_exception_only(etype, value):
string in the list.
"""
return list(_format_exception_only_iter(etype, value))
return list(TracebackException(etype, value, None).format_exception_only())
def _format_exception_only_iter(etype, value):
# Gracefully handle (the way Python 2.4 and earlier did) the case of
# being called with (None, None).
if etype is None:
yield _format_final_exc_line(etype, value)
return
stype = etype.__qualname__
smod = etype.__module__
if smod not in ("__main__", "builtins"):
stype = smod + '.' + stype
if not issubclass(etype, SyntaxError):
yield _format_final_exc_line(stype, value)
return
# It was a syntax error; show exactly where the problem was found.
filename = value.filename or "<string>"
lineno = str(value.lineno) or '?'
yield ' File "{}", line {}\n'.format(filename, lineno)
badline = value.text
offset = value.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 = value.msg or "<no detail available>"
yield "{}: {}\n".format(stype, msg)
# -- not offical 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:
if value == 'None' or value is None or not valuestr:
line = "%s\n" % etype
else:
line = "%s: %s\n" % (etype, valuestr)
@ -247,6 +144,8 @@ def _some_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)
@ -267,15 +166,6 @@ def print_last(limit=None, file=None, chain=True):
# Printing and Extracting Stacks.
#
def _extract_stack_iter(f, limit=None):
return _extract_tb_or_stack_iter(
f, limit, lambda f: (f, f.f_lineno, f.f_back))
def _get_stack(f):
if f is None:
f = sys._getframe().f_back.f_back
return f
def print_stack(f=None, limit=None, file=None):
"""Print a stack trace from its invocation point.
@ -283,11 +173,13 @@ def print_stack(f=None, limit=None, file=None):
stack frame at which to start. The optional 'limit' and 'file'
arguments have the same meaning as for print_exception().
"""
print_list(extract_stack(_get_stack(f), limit=limit), file=file)
print_list(extract_stack(f, limit=limit), file=file)
def format_stack(f=None, limit=None):
"""Shorthand for 'format_list(extract_stack(f, limit))'."""
return format_list(extract_stack(_get_stack(f), limit=limit))
return format_list(extract_stack(f, limit=limit))
def extract_stack(f=None, limit=None):
"""Extract the raw traceback from the current stack frame.
@ -298,10 +190,11 @@ def extract_stack(f=None, limit=None):
line number, function name, text), and the entries are in order
from oldest to newest stack frame.
"""
stack = list(_extract_stack_iter(_get_stack(f), limit=limit))
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:
@ -311,3 +204,328 @@ def clear_frames(tb):
# 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 str() 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
strings.
: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, str(v)) for k, v in locals.items()) if locals else None
def __eq__(self, other):
return (self.filename == other.filename and
self.lineno == other.lineno and
self.name == other.name and
self.locals == other.locals)
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):
"""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.
"""
if limit is None:
limit = getattr(sys, 'tracebacklimit', None)
result = klass()
fnames = set()
for pos, (f, lineno) in enumerate(frame_gen):
if limit is not None and pos >= limit:
break
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.
result.append(FrameSummary(filename, lineno, name, lookup_line=False))
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.
"""
if isinstance(a_list, StackSummary):
return StackSummary(a_list)
result = StackSummary()
for filename, lineno, name, line in a_list:
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 filename, lineno, name, line in self:
item = ' File "{}", line {}, in {}\n'.format(filename, lineno, name)
if line:
item = item + ' {}\n'.format(line.strip())
result.append(item)
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
occured.
- :attr:`lineno` For syntax errors - the linenumber where the error
occured.
- :attr:`text` For syntax errors - the text where the error
occured.
- :attr:`offset` For syntax errors - the offset into the text where the
error occured.
- :attr:`msg` For syntax errors - the compiler error message.
"""
def __init__(self, exc_type, exc_value, exc_traceback, limit=None,
lookup_lines=True, _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,
_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,
_seen=_seen)
else:
context = None
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)
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
yield 'Traceback (most recent call last):\n'
yield from self.stack.format()
yield from self.format_exception_only()

View File

@ -441,6 +441,13 @@ Library
now clears its internal reference to the selector mapping to break a
reference cycle. Initial patch written by Martin Richard.
- Issue #17911: Provide a way to seed the linecache for a PEP-302 module
without actually loading the code.
- Issue #17911: Provide a new object API for traceback, including the ability
to not lookup lines at all until the traceback is actually rendered, without
any trace of the original objects being kept alive.
- Issue #19777: Provide a home() classmethod on Path objects. Contributed
by Victor Salgado and Mayank Tripathi.