[issue21771] name of 2nd parameter to itertools.groupby()

[Raymond Hettinger]

Raymond Hettinger added the comment:

There is a bit an inconsistency but it is more helpful than harmful most of the 
time.  The glossary defines a key-function which is used in a number of places 
such such as sorted(), min(), nsmallest() and others.  In all those cases, the 
parameter for the key-function is *key*.

It might feel "more consistent" to call it "key" everywhere, but that leaves 
out the explanation that *key* represents a key-function.

The other issue is that groupby() returns a (key, sub-iterator) pair where 
"key" is the result of key-function, not the key itself.

What we have now is imperfect but it does a reasonably good job helping people 
understand what the function does.  IMO, changing it to be "key" would make the 
docs less intelligible.

Thank you for the patch, but I'm going to pass on it.

--
resolution:  -> rejected
status: open -> closed

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[issue21771] name of 2nd parameter to itertools.groupby()

[Ned Deily]

Changes by Ned Deily :


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nosy: +rhettinger

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[issue21771] name of 2nd parameter to itertools.groupby()

[Uwe Kleine-König]

New submission from Uwe Kleine-König:

The name of the 2nd parameter to itertools.groupby() is documented 
inconsitently. Sometimes it's "key", sometimes "keyfunc". The code actually 
uses "key", so I adapted all occurences I found to "key".

>>> from itertools import groupby
>>> groupby.__doc__
'groupby(iterable[, keyfunc]) -> create an iterator which returns\n(key, 
sub-iterator) grouped by each value of key(value).\n'

>>> groupby([], keyfunc=lambda x: x)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: 'keyfunc' is an invalid keyword argument for this function

>>> groupby([], key=lambda x: x)


--
assignee: docs@python
components: Documentation
files: groupby-keyfunc.patch
keywords: patch
messages: 220639
nosy: docs@python, ukl
priority: normal
severity: normal
status: open
title: name of 2nd parameter to itertools.groupby()
type: enhancement
versions: Python 2.7, Python 3.3, Python 3.4, Python 3.5
Added file: http://bugs.python.org/file35645/groupby-keyfunc.patch

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