[issue19145] Inconsistent behaviour in itertools.repeat when using negative times

[Larry Hastings]

Larry Hastings added the comment:

For what it's worth: I figured out how this happened.  Maybe it's obvious to you, but this behavior baffled me until I went back and looked at the revision history.

In revision e260d6daf784, the argument parsing for itertools.repeat looks like this:

    Py_ssize_t cnt = -1;

    if (type == &repeat_type && !_PyArg_NoKeywords("repeat()", kwds))
        return NULL;

    if (!PyArg_ParseTuple(args, "O|n:repeat", &element, &cnt))
        return NULL;

    if (PyTuple_Size(args) == 2 && cnt < 0)
        cnt = 0;

In the subsequent revision, 3dbdbc5e6d85, it was changed to this:

    Py_ssize_t cnt = -1;

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|n:repeat", kwargs,
                                     &element, &cnt))
        return NULL;

    if (PyTuple_Size(args) == 2 && cnt < 0)
        cnt = 0;

The original intent is now clear: only allow "cnt" to be -1 if it wasn't specified as an argument.  The author simply forgot that "times" could now be passed in as a keyword argument too.

What the author *probably* wanted was something like this:

    PyObject *times_keyword;

    ...

    times_keyword = PyDict_GetItemString(kwargs, "times");
    Py_XDECREF(times_keyword);
    if ((PyTuple_Size(args) == 2 || times_keyword) && cnt < 0)
        cnt = 0;

But I suggest it's far too late to change it to that now.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue19145>
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