Le dim. 3 oct. 2021 à 16:21, <python-ideas-request@python.org> a écrit :
Date: Mon, 4 Oct 2021 01:03:34 +1100
From: Steven D'Aprano <steve@pearwood.info>
Subject: [Python-ideas] Re: Feature request enumerate_with_rest or
enumerate with skip or filter callback
To: python-ideas@python.org
Message-ID: <20211003140333.GR16229@ando.pearwood.info>
Content-Type: text/plain; charset=us-ascii
Hi Laurent,
Hello Steve,
It is not clear to me what you mean by "filter by indices".
On Sat, Oct 02, 2021 at 10:25:05PM +0200, Laurent Lyaudet wrote:
The idea is to filter a list by indices :
[...]
Since filter() returns an iterator instead of a list, it could do what
is needed... if the callback had access to the index like the
Javascript array filter function.
Do you mean this?
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Obj...
Yes exactly,
You shouldn't assume we are all experts on Javascript :-)
No problem, I'll give more links next time :)
If that is what you want, it is easy to get access to the index. We can
just do:
filter(function, enumerate(items))
That's exactly what I proposed. Except for the fact that I incorrectly
permuted the two arguments of filter.
I quote my second email :
Le sam. 2 oct. 2021 à 22:35, <python-ideas-request@python.org> a écrit :
Date: Sat, 2 Oct 2021 22:25:05 +0200
From: Laurent Lyaudet <laurent.lyaudet@gmail.com>
...
Currently, the following solution is available :
filter(enumerate(my_list), lambda x: x[0] != i)
But it is slightly ugly and unefficient to have two function calls for
such a simple task I think.
I feel uncomfortable because it is often the case that I write
explicitly something,
and I get an answer as if the person answered without reading all my
email or reading another version.
If you want something else, I'm afraid you will have to explain in more
detail what you want, sorry.
What would be your prefered way of doing this ?
enumerate(my_list, filter_callback=(lambda x: x != i))
filter_by_index(my_list, lambda x: x != i)
# à la JS
filter(my_list, lambda _, x: x != i)
filter_by_index(lambda x: x != i, my_list)
could be defined as follow (I permuted args to have similar order to
Again for my second email, I would like one of these 3 options.
python's filter()):
def filter_by_index(function, my_list):
for i, item in enumerate(my_list)
if function(i):
yield item
like filter is just (without the case function=None)
filter(function, my_list):
for i, item in enumerate(my_list)
if function(item):
yield item
The problem is not that it is hard to code in Python.
The problem is that it is a basic building block for an iterators
tools library like itertools.
enumerate(my_list, filter_callback=(lambda x: x != i))
could be defined in a similar way but there are two variants.
It just needs to return one of the two indices of the item:
- either the index of the item in the original sequence,
- or the index of the item in the filtered sequence (new counter).
For my use case, I do not need the index so I have no argument in
favor of either one of the two indices.
# à la JS
filter(my_list, lambda _, x: x != i)
You provided the link from MDN and an helper function for that.
The lambda takes 2 or 3 parameters: item, index, array/list/sequence
and returns true for item that must be output.
I see nothing more to say.
Best regards,
Laurent Lyaudet
Laurent Lyaudet