New issue 2034: PyPy Regression with Python on Iterable expansions https://bitbucket.org/pypy/pypy/issue/2034/pypy-regression-with-python-on-iterable
Pedro Rodriguez: I am the main developer on github.com/EntilZha/ScalaFunctional and in working on it I found a regression with Python. I don't know if it is an intended regression, but it caused some unexpected behavior which I was able to narrow down. If you want the full explanation, it is on the issue on the project here: https://github.com/EntilZha/ScalaFunctional/issues/25 Below is a minimal code example showing the regression between pypy and python. The primary problem is how `pypy` is doing expansions of iterables (`list()`, `set()`, `dict()`, ...). When those are expanded `pypy` will call `__iter__`, then `__len__`. Python will only call `__iter__`. ``` #!python from collections import Iterable class A(object): def __init__(self, seq): self.l = seq def __getitem__(self, item): print "DEBUG:getitem called" return self.l[item] def __iter__(self): print "DEBUG:iter called" return iter(self.l) def __len__(self): print "DEBUG:len called" if isinstance(self.l, Iterable): self.l = list(self.l) return len(self.l) class B(object): def __init__(self, seq): self.l = seq def __iter__(self): print "DEBUG:iter called" return iter(self.l) # set interchangable with list/dict print "Calling set(A([1, 2]))" a = A([1, 2]) print set(a) print "Calling set(B([1, 2]))" b = B([1, 2]) print set(b) print "Calling union" s = set([1, 2, 3]).union([4, 5]) c = A(iter(s)) print set(c) ``` ``` #!python $ python iterable.py Calling set(A([1, 2])) DEBUG:iter called set([1, 2]) Calling set(B([1, 2])) DEBUG:iter called set([1, 2]) Calling union DEBUG:iter called set([1, 2, 3, 4, 5]) $ pypy iterable.py Calling set(A([1, 2])) DEBUG:len called DEBUG:iter called [1, 2] Calling set(B([1, 2])) DEBUG:iter called set([1, 2]) Calling union DEBUG:iter called DEBUG:len called set([]) ``` In my code, the solution would be fairly easy to do type checking and not rewrap the iterator within another iterator. Regardless, since I am unfamiliar with `pypy` I don't know if the regression is intended or unintended. _______________________________________________ pypy-issue mailing list pypy-issue@python.org https://mail.python.org/mailman/listinfo/pypy-issue
