On Thu, 5 Sep 2019 at 11:19, <r...@hwyl.org> wrote:
> I find a common requirement I have is to include one or more entries in a
> dict only if some condition is met. Currently, the usual way of doing that is
> to add one or more if statements.
>
> Simple (but hopefully relatable-to-real-world-code) example.
[...]
> This is a fairly common (tedious) pattern in my code, but I feel it could be
> avoided. In my view it would be better if it was possible to conditionally
> add the entry in the dict declaration.
>
> My proposal is that there should be a special value defined that results in a
> dict entry not being added to the dict if either the key or the value equals
> this value. There may be several ways to achieve this, but here's one way it
> could work.
This is pretty easy to write as a helper function:
>>> def dct(**kw):
... return {k:v for k, v in kw.items() if v is not dct.skip}
...
>>> dct.skip = object()
>>>
>>> dct(a=12, b=None, c=dct.skip, d="Hello", e=dct.skip)
{'a': 12, 'b': None, 'd': 'Hello'}
Given this, I'm not sure it's a sufficiently useful improvement to be
worth adding to the builtin dictionary (although thanks for the
suggestion, I wouldn't have ever thought about writing a helper to
avoid the boilerplate without this posting to prompt me!)
Paul
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