Ned Batchelder wrote: > On 3/15/18 9:57 AM, Vlastimil Brom wrote: >> 2018-03-15 12:54 GMT+01:00 Arkadiusz Bulski <arek.bul...@gmail.com>: >>> I have a custom class (a lazy list-like container) that needs to support >>> slicing. The __getitem__ checks if index is of slice type, and does a >>> list comprehension over individual integer indexes. The code works fine >>> on Python 3 but fails on 2.7, both CPython and PyPy. The print inside >>> __getitem__ doesnt even get executed when its a slice. Does 2.7 have >>> different object model, where slices are handled by a different method >>> than __getitem__? >>> >>> The implementation and error log >>> https://github.com/construct/construct/blob/8839aac2b68c9e8240e9d9c041a196b0a7aa7d9b/construct/core.py#L4785-L4796 >>> https://github.com/construct/construct/blob/8839aac2b68c9e8240e9d9c041a196b0a7aa7d9b/tests/test_core.py#L1148 >>> https://travis-ci.org/construct/construct/jobs/353782126#L887 >>> >>> -- >>> ~ Arkadiusz Bulski >>> -- >>> https://mail.python.org/mailman/listinfo/python-list >> Hi, >> it looks like, the older method __getslice__ is still used in python 2.7 >> cf.: >> https://docs.python.org/2/reference/datamodel.html#object.__getslice__ >> >> You might need to implement this method in your class as well for >> compatibility with python 2. >> >> > > Python 2 will use __getitem__ for slices: > > $ python2.7 > Python 2.7.10 (default, May 30 2015, 12:06:13) > [GCC 4.2.1 Compatible Apple LLVM 6.1.0 (clang-602.0.53)] on darwin > Type "help", "copyright", "credits" or "license" for more information. > >>> class Sliceable(object): > ... def __getitem__(self, thing): > ... print type(thing) > ... print thing > ... > >>> Sliceable()[1:5] > <type 'slice'> > slice(1, 5, None) > >>> Sliceable()[:] > <type 'slice'> > slice(None, None, None) > >>>
__getslice__() takes precedence, and the OP subclasses list: $ python Python 2.7.6 (default, Nov 23 2017, 15:49:48) [GCC 4.8.4] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> class A(list): ... def __getitem__(self, index): return index ... >>> a = A() >>> a[:] [] >>> a[::] slice(None, None, None) >>> A.__getslice__ = lambda self, *args: args >>> a[:] (0, 9223372036854775807) -- https://mail.python.org/mailman/listinfo/python-list
