New submission from Elvis Pranskevichus <elpr...@gmail.com>: Consider the following:
>>> class Test: ... def __init__(self): ... self.items = [] ... def __len__(self): ... if not self.items: ... self.items = list(self.calc_items()) ... return len(self.items) ... def __iter__(self): ... return iter(self.items) ... def calc_items(self, number): ... return range(1, number) ... >>> l = list(Test()) >>> print(l) [] >>> t = tuple(Test()) >>> print(t) () In the above example calc_items() method is called with a missing argument, which raises TypeError. That TypeError is being wrongly interpreted as "object of type 'Test' has no len()" and is swallowed by _PyObject_LengthHint(). The result is entirely unpredictable as the bug is masked, which is especially annoying for objects that can have a complex call graph under __len__(). Possible solution would be to adjust _PyObject_LengthHint() to rely on some other exception rather than straight TypeError. Swallowing a generic exception like that is bad. ---------- components: Interpreter Core messages: 132150 nosy: Elvis.Pranskevichus priority: normal severity: normal status: open title: list(obj), tuple(obj) swallow TypeError (in _PyObject_LengthHint) type: behavior versions: Python 2.5, Python 2.6, Python 2.7, Python 3.1, Python 3.2, Python 3.3 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue11674> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
