[Python-Dev] integer subclass range behavior

[Guido van Rossum]

Can you submit a bug at bugs.python.org?

The minimal example I found:

>>> class a(int): pass
...
>>> for i in range(0, a(5)): pass
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: Objects/longobject.c:400: bad argument to internal function
>>>


On Dec 19, 2007 5:38 PM, Joseph Armbruster <josepharmbruster at gmail.com> wrote:
> All,
>
> I posted this up to comp.lang.python earlier today and asked a few questions
> around IRC.  The general consensus appeared to be that this was a bug.  Before
> opening up an issue on it, I wanted to run it by this list first (just in case)
>   Here is a copy / paste from comp.lang.python:
>
> URL:
>
> http://groups.google.com/group/comp.lang.python/browse_frm/thread/801f227fceff4066#e0305608a5931af1
>
> Post:
>
> I was wondering what would happen, so I tried this out for the heck of it with:
> Python 3.0a2 (py3k:59572M, Dec 19 2007, 15:54:07) [MSC v.1500 32 bit (Intel)]
> on win32
>
> class a(int):
>    def __new__(cls,number):
>      return int.__new__(cls,number)
>
> for x in range(0,a(5)):
>    print(x)
>
> Which resulted in a:
>
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
>    File "a.py", line 5, in <module>
>      for x in range(0,a(5)):
> SystemError: ..\Objects\longobject.c:400: bad argument to internal
> function
> [41030 refs]
>
> It looks like the rangeobject performs a FitsInLong test on each of
> the parameters to range, which uses the function
> _PyLong_FitsInLong(PyObject *vv) within longobject.c.  In tern, this
> performs a typecheck:  #define PyLong_CheckExact(op) (Py_TYPE(op) ==
> &PyLong_Type) that fails.
>
> Interesting!
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--Guido van Rossum (home page: http://www.python.org/~guido/)