In itertools.chain.from_iterable() there is no cls argument #62501

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1. py-user commented on Jun 25, 2013

   

   py-usermannequin

   on Jun 25, 2013

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   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
   >>>
2. py-user

   assigned

   docspython

   on Jun 25, 2013
3. py-user

   added

   docsDocumentation in the Doc dirDocumentation in the Doc dir

   type-featureA feature request or enhancementA feature request or enhancement

   on Jun 25, 2013
4. py-user commented on Jun 25, 2013

   

   py-usermannequin

   on Jun 25, 2013

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   http://docs.python.org/3/library/itertools.html#itertools.chain.from_iterable
5. bitdancer commented on Jun 25, 2013

   

   bitdancer

   on Jun 25, 2013

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   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.
6. terryjreedy commented on Jun 28, 2013

   

   terryjreedy

   on Jun 28, 2013

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   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.
7. serhiy-storchaka commented on Jun 28, 2013

   

   serhiy-storchaka

   on Jun 28, 2013

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   Perhaps it should be staticmethod, not classmethod.
8. serhiy-storchaka commented on Aug 6, 2013

   

   serhiy-storchaka

   on Aug 6, 2013

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   It should be a classmethod.

   >>> import itertools
   >>> class C(itertools.chain): pass
   ... 
   >>> type(C.from_iterable(['ab', 'cd']))
   <class '__main__.C'>

   The patch LGTM.
9. serhiy-storchaka

   assigned

   serhiy-storchaka

   and

   rhettinger

   and unassigned

   docspython

   and

   serhiy-storchaka

   on Aug 6, 2013
10. ezio-melotti commented on Aug 8, 2013

    

    ezio-melotti

    on Aug 8, 2013

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    I would just remove the decorator.

    +1
11. py-user commented on Aug 8, 2013

    

    py-usermannequin

    on Aug 8, 2013

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    >>> 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
12. py-user commented on Aug 9, 2013

    

    py-usermannequin

    on Aug 9, 2013

    MannequinAuthor

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    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
    >>>
13. terryjreedy commented on Aug 15, 2013

    

    terryjreedy

    on Aug 15, 2013

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    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.
14. python-dev commented on Sep 9, 2013

    

    python-devmannequin

    on Sep 9, 2013

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    New changeset 29fa1f418796 by Raymond Hettinger in branch '3.3':
    bpo-18301: The classmethod decorator didn't fit well with the rough-equivalent example code.
    http://hg.python.org/cpython/rev/29fa1f418796
15. rhettinger

    closed this as completedon Sep 9, 2013
16. ezio-melotti

    transferred this issue fromon Apr 10, 2022