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In itertools.chain.from_iterable() there is no cls argument #62501Description
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GitHub fields:
assignee = 'https://github.com/rhettinger'
closed_at = <Date 2013-09-09.06:57:17.906>
created_at = <Date 2013-06-25.18:58:43.184>
labels = ['type-feature', 'docs']
title = 'In itertools.chain.from_iterable() there is no cls argument'
updated_at = <Date 2013-09-09.06:57:17.905>
user = 'https://github.com/py-user' bugs.python.org fields:
activity = <Date 2013-09-09.06:57:17.905>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2013-09-09.06:57:17.906>
closer = 'rhettinger'
components = ['Documentation']
creation = <Date 2013-06-25.18:58:43.184>
creator = 'py.user'
dependencies = []
files = ['30702']
hgrepos = []
issue_num = 18301
keywords = ['patch']
message_count = 11.0
messages = ['191874', '191875', '191884', '192009', '192015', '194535', '194668', '194701', '194712', '195291', '197352']
nosy_count = 8.0
nosy_names = ['rhettinger', 'terry.reedy', 'ezio.melotti', 'r.david.murray', 'docs@python', 'py.user', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'commit review'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue18301'
versions = ['Python 3.3', 'Python 3.4'] Activitypy-user commented on Jun 25, 2013 MannequinAuthor More actions http://docs.python.org/2/library/itertools.html#itertools.chain.from_iterable
>>> class A:
... @classmethod
... def from_iterable(iterables):
... for it in iterables:
... for element in it:
... yield element
...
>>> A.from_iterable(['ABC', 'DEF'])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: from_iterable() takes 1 positional argument but 2 were given
>>> py-user commented on Jun 25, 2013 MannequinAuthor More actions bitdancer commented on Jun 25, 2013 It is implemented as a classmethod, but the "equivalent" code doesn't need to be part of the class all. I'm not sure what should be done here (say @staticmethod? Leave the decorator off?). We should probably see what Raymond thinks. I lean toward the latter, that's the way it is in the python2 docs, and it doesn't seem to have caused any confusion. terryjreedy commented on Jun 28, 2013 The 2.7 doc says 'Roughly equivalent to' rather than 'Equivalent to'.
The undecorated Python version of from_iterable actually works as an attribute of the Python version of chain: chain.from_iterable = from_iterable. I would just remove the decorator. The entire itertools doc exploits that fact that generator functions are analogous to classes, but it does not work to mix the two in the way that the 3.x chain entry does. serhiy-storchaka commented on Jun 28, 2013 Perhaps it should be staticmethod, not classmethod. serhiy-storchaka commented on Aug 6, 2013 It should be a classmethod.
>>> import itertools
>>> class C(itertools.chain): pass
...
>>> type(C.from_iterable(['ab', 'cd']))
<class '__main__.C'> The patch LGTM. ezio-melotti commented on Aug 8, 2013
I would just remove the decorator.
+1 py-user commented on Aug 8, 2013 MannequinAuthor More actions >>> import itertools
>>>
>>> class A(itertools.chain):
... def from_iter(arg):
... return A(iter(arg))
...
>>> class B(A):
... pass
...
>>> B('a', 'b')
<__main__.B object at 0x7f40116d7730>
>>> B.from_iter(['a', 'b'])
<__main__.A object at 0x7f40116d7780>
>>>it should be B py-user commented on Aug 9, 2013 MannequinAuthor More actions changed iter(arg) to *arg
>>> import itertools
>>>
>>> class A(itertools.chain):
... @classmethod
... def from_iter(cls, arg):
... return cls(*arg)
...
>>> class B(A):
... pass
...
>>> B('ab', 'cd')
<__main__.B object at 0x7fc280e93cd0>
>>> b = B.from_iter(['ab', 'cd'])
>>> b
<__main__.B object at 0x7fc280e93d20>
>>> next(b)
'a'
>>> next(b)
'b'
>>> next(b)
'c'
>>> next(b)
'd'
>>> next(b)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
>>>terryjreedy commented on Aug 15, 2013 My counter proposal bpo-18752 is that chain.from_iterable become a deprecated alias for a new function, chain_iterable. With '@classmethod' removed, the current Python equivalent would work for chain_iterable. python-dev commented on Sep 9, 2013
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