[Patches] [ python-Patches-1660179 ] functools.compose to chain functions together

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Thu Feb 15 13:47:11 CET 2007


Patches item #1660179, was opened at 2007-02-15 10:17
Message generated for change (Comment added) made by ncoghlan
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Category: Library (Lib)
Group: Python 2.6
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Chris AtLee (catlee)
Assigned to: Martin v. Löwis (loewis)
Summary: functools.compose to chain functions together

Initial Comment:
The motivation for this patch was to be able to chain together operator.itemgetter objects so that I could sort a list of items that have the form ((a,b), c) by the 'a' or 'b' part of the item.

Sorting by 'b' can be accomplished with:
l.sort(key=compose(itemgetter(1), itemgetter(0)))

compose(itemgetter(1), itemgetter(0)) is equivalent to

def c(v):
    return itemgetter(1)(itemgetter(0)(v))

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>Comment By: Nick Coghlan (ncoghlan)
Date: 2007-02-15 22:47

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Patch quality also looks good to me.

However, my main concerns would be whether or not the use case comes up
often enough to justify inclusion in the standard library, and at what
point it makes more sense to just use a lambda expression. For example, I
think most people would find this easier to understand than the compose
based version:

    l.sort(key=(lambda k: k[0][1]))


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Comment By: Georg Brandl (gbrandl)
Date: 2007-02-15 20:25

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The patch looks good, is complete (one nit, "Returns" should be "Return"
in the doc) and the functionality belongs into functools.
What do you think, Martin?

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