New submission from Tim Hatch <[email protected]>:
inspect.findsource() can trigger IndexError when co_firstlineno is larger than
len(linecache.getlines()).
If you have a situation where the file that linecache finds doesn't match the
imported module, then you're not guaranteed that co_firstlineno on the code
objects makes any sense. We hit this in a special kind of par file, but it
could be triggered by shortening the file, like doing a git checkout of an
older version while it's running.
a.py (3 lines):
# line 1
# line 2
def foo(): pass # co_firstlineno=3
a.py.v2 (1 line):
def foo(): pass
repro:
import a
# modification happens, cp a.py.v2 a.py
inspect.getsource(a.foo)
Although linecache.getline() does bounds checking, `inspect.findsource()`
(which is used by various other functions, including `inspect.stack()`) grabs
all the lines and loops through them. The bug is in this section of
`inspect.py`:
if iscode(object):
if not hasattr(object, 'co_firstlineno'):
raise OSError('could not find function definition')
lnum = object.co_firstlineno - 1
pat =
re.compile(r'^(\s*def\s)|(\s*async\s+def\s)|(.*(?<!\w)lambda(:|\s))|^(\s*@)')
while lnum > 0:
if pat.match(lines[lnum]): break
lnum = lnum - 1
return lines, lnum
raise OSError('could not find code object')
Found through future.utils.raise_from which actually doesn't need to be using
`inspect.stack()`, it can switch to `sys._getframe(2)` or so. We should have a
PR ready shortly, but wondering if this can be backported to at least 3.6?
----------
components: Library (Lib)
messages: 344761
nosy: lisroach, thatch, vstinner
priority: normal
severity: normal
status: open
title: inspect.findsource doesn't handle shortened files gracefully
versions: Python 3.6, Python 3.7, Python 3.8
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Python tracker <[email protected]>
<https://bugs.python.org/issue37166>
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