[issue14611] inspect.getargs fails on some anonymous tuples

[Stefano Taschini]

New submission from Stefano Taschini <taschini at ieee.org>:

How to reproduce
----------------

Take the following two functions:

    >>> def f(l, (x, y)):
    ...    sup = max(u*x + v*y for u, v in l)
    ...    return ((u, v) for u, v in l if u*x + v*y == sup)

    >>> def g((x, y)):
    ...    def h():
    ...        return x + y
    ...    return h

Inspect.getargs will throw an exception on the former and return a wrong
result on the latter::

    >>> import inspect
    >>> inspect.getargs(f.__code__)
    Traceback (most recent call last):
    ...
    IndexError: list index out of range

    >>> inspect.getargs(g.__code__)
    Arguments(args=['h'], varargs=None, keywords=None)

    # h is most definitely not an argument of g!

Analysis
--------

If you disassemble the two functions, you'll see that in both cases
the anonymous tuples are unpacked using STORE_DEREF::

    >>> import dis
    >>> dis.disassemble(f.__code__)
      1           0 LOAD_FAST                1 (.1)
                  3 UNPACK_SEQUENCE          2
                  6 STORE_DEREF              0 (x)
                  9 STORE_DEREF              2 (y)
    <BLANKLINE>
      2          12 LOAD_GLOBAL              0 (max)
    ...

    >>> dis.disassemble(g.__code__)
      1           0 LOAD_FAST                0 (.0)
                  3 UNPACK_SEQUENCE          2
                  6 STORE_DEREF              0 (x)
                  9 STORE_DEREF              1 (y)
    <BLANKLINE>
      2          12 LOAD_CLOSURE             1 (y)
                 15 LOAD_CLOSURE             0 (x)
                 18 BUILD_TUPLE              2
                 21 LOAD_CONST               1 (<code object h ...>)
                 24 MAKE_CLOSURE             0
                 27 STORE_FAST               3 (h)
    <BLANKLINE>
      4          30 LOAD_FAST                3 (h)
                 33 RETURN_VALUE        \


However, the implementation of inspect.getargs only looks for
UNPACK_TUPLE, UNPACK_SEQUENCE, STORE_FAST.

Notes
-----

The version of Python used is::

    >>> import sys
    >>> sys.version_info[:3]
    (2, 7, 3)

----------
components: Library (Lib)
messages: 158599
nosy: taschini
priority: normal
severity: normal
status: open
title: inspect.getargs fails on some anonymous tuples
type: behavior
versions: Python 2.7

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue14611>
_______________________________________