> The signature is wrong.
Thanks for remark. Of course proper signature would be:
def jin(a: Iterable[Optional[str]], sep=“ “):
# …
> Why do you (ab)use compress for that?
Well, it seems that it is subjective. To me “[None, x, y, z]” -> “[x, y, z]”
looks like “compression”. But if community agrees with your side, then, well,
it’s OK.
As another argument to use “compress” was similar case I found on stackoverflow
for numpy:
https://stackoverflow.com/questions/5927180/how-do-i-remove-all-zero-elements-from-a-numpy-array
So extending “compress” would be useful for math cases as well.
Alternatively indeed we can use:
2. Use "filter(None, a)”
3. (x for x in a if x)
Why not to use #3?
Only having #2 or #3, I would vote for “filter”. It is a builtin, and used to
be implemented as intrinsic. In cpython it has a separate “if” branch for case
when first argument is “None” (see “filter_next” function in “bltinmodule.c”)
There is also a good chance to work with optimized “compress” one day.
#3 semantically is more complicated and it seems that there are no
optimizations at least in cpython (but perhaps I’m wrong?). So, it looks like
#3 is slower while parsing and while executing.
#3 is bad choice for code maintenance. It is always better to pass variable
once. “(x for x in a if x)” contains micro code dups. Here, you put “x” three
times, and then if you decide to use something else you have to edit it in
three places. So #3 defeats if you want to reuse or just maintain such code.
Paul confirmed my worries about “jin”, so it seems that it is not an option
either.
And yet, I still have a little hope about original proposal. I proposed to add
default value for second argument of “compress”.
So thanks for you attention anyways, and let me know if it is still has a
chance to be accepted.
Thanks!
Stepan Dyatkovskiy.
> On Sep 14, 2021, at 2:18 PM, Steven D'Aprano <st...@pearwood.info> wrote:
>
> On Tue, Sep 14, 2021 at 11:31:43AM +0400, m...@dyatkovskiy.com wrote:
>
>> Thus I have collection of options and some of them are empty or None.
>> In order to get rendered command line options string I use “compress”
>> in conjunction with “join":
>>
>>>>> opts = " ".join(compress(flags, flags))
>
> Why do you (ab)use compress for that?
>
> I understand that `compress(flags, flags)` has the effect of filtering
> for non-empty flags. But that's an obfuscated way to write it. Either of
> these would be more understandable:
>
> * `filter(None, flags)` # could also use bool instead of None
>
> * `(flag for flag in flags if flag)`
>
> especially the last, although heavy users of functional languages may
> prefer filter. But using compress with the same argument twice is just
> weird.
>
> And also fragile. You can't use an iterator for the flags.
>
>>>> jin(iter(['a', 'b', '', 'c', 'd', 'e', 'f', '', 'g']))
> 'a d'
>
>
>> I usually introduce alias for this:
>>
>>>>> def jin(a: str, sep=“ “):
>>>>> return sep.join(compress(a, a))
>>
>> And I found that I use it quite frequently.
>
> The signature is wrong. `flags` is a list of string options. If you pass
> an actual string, you expand it with spaces:
>
>
>>>> jin('abc def')
> 'a b c d e f'
>
>
> --
> Steve
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