Empty list as a default param - the problem, and my suggested solution
Martin Di Paola
martinp.dipaola at gmail.com
Sat Aug 14 19:40:07 EDT 2021
I don't know if it is useful but it is an interesting
metaprogramming/reflection challenge.
You used `inspect` but you didn't take its full potential. Try to see if
you can simplify your code and see if you can come with a decorator
that does not require special parameters.
>>> from new import NEW
>>> @NEW
... def new_func(a=[]):
... a.append('new appended')
... return a
...
>>> new_func()
['new appended']
>>> new_func()
['new appended']
Spoiler - My solution is at
https://book-of-gehn.github.io/articles/2021/08/14/Fresh-Python-Defaults.html
On Fri, Aug 13, 2021 at 03:44:20PM -0700, guruyaya wrote:
>I am fairly sure all of us know about this python quirk:
>>>> def no_new_func(a=[]):
>... a.append('new')
>... return a
>
>>>> no_new_func()
>['new']
>>>> no_new_func()
>['new', 'new']
>>>>
>
>For some time I was bothered about that there's no elegant way to use empty list or dict as a default parameter. While this can be solved like this:
>>>> def no_new_func(a=None):
>... if a == None:
> a = []
>... a.append('new')
>... return a
>
>I have to say I find this solution very far from the spirit of python. Kinda ugly, and not explicit. So I've decided to try and create a new module, that will try and make, what I think, is a more beautiful and explicit:
>
>>>> from new import NEW
>>>> @NEW.parse
>... def new_func(a=NEW.new([])):
>... a.append('new appended')
>... return a
>...
>>>> new_func()
>['new appended']
>>>> new_func()
>['new appended']
>
>I'd like to hear your thoughts on my solution and code. You can find and give your feedback in this project
>https://github.com/guruyaya/new
>If I see that people like this, I will upload it to pip. I'm not fully sure about the name I choose (I thought about the "new" keyword used in JAVA, not sure it applies here as well)
>
>Thanks in advance for your feedback
>Yair
>--
>https://mail.python.org/mailman/listinfo/python-list
More information about the Python-list
mailing list