I had a similar solution with a decorator using inspect.getfullargspec but it is pretty fiddly and it is pretty easy to miss some of the edge cases. Having a standard implementation would definitely take care of this. And I imagine static analysis tools would be able to cope with it, they do a good job with all of the current language features!
On Mon, 4 May 2020, 22:11 Steele Farnsworth, <swfarnswo...@gmail.com> wrote: > I agree that dataclasses are for a slightly different use case. > > It looks like this could be implemented as a decorator using the > functionality afforded by `inspect.signature`, though what I've come up > with so far is a bit clunky because you have to account for parameters that > could be positional or keyword and assigning default values for missing > arguments. > > If this were added, I assume that static analysis tools would need to be > updated to account for the assumption that each instance has attributes > with the same names that appear in the `__init__` signature, and I have no > idea what that would entail. It would probably pose a similar issue for > automated refactoring. > > On Mon, May 4, 2020 at 4:48 PM Lewis Ball <lrjb...@gmail.com> wrote: > >> I did think about data classes and although I haven't really used them >> much they do seem to be for a different use case, for example they don't >> support keyword-only args or positional-only args. I'm not sure if there >> are any other differences. Maybe a data class which supported kW-only args >> and pos-only args would suit my use case. >> >> On Mon, 4 May 2020, 21:19 Henk-Jaap Wagenaar, <wagenaarhenkj...@gmail.com> >> wrote: >> >>> You are not the first to have this idea. Unless I am mistaken you might >>> find what you are looking for in dataclasses which were added in Python 3.7: >>> >>> https://docs.python.org/3/library/dataclasses.html >>> >>> On Mon, 4 May 2020 at 19:06, Lewis Ball <lrjb...@gmail.com> wrote: >>> >>>> Hi All, >>>> >>>> First of all, if this is something which has been discussed in the past >>>> the please point me in the right direction. >>>> >>>> *Problem:* >>>> >>>> When creating classes in Python, I find myself writing the __init__ >>>> method in a very similar way a lot of the time, that is: >>>> ``` >>>> def __init__(self, argument_1, argument_2, argument_3=None): >>>> self.argument_1 = argument_1 >>>> self.argument_2 = argument_2 >>>> self.argument_3 = argument_3 >>>> # then maybe some other attribute setting and logic follows >>>> ``` >>>> >>>> Every argument of __init__ gets a corresponding attribute with the same >>>> name. This means that each `argument_i` has been typed 3 times, which seems >>>> overly-verbose as well as being easy to mistype. This pattern is easy to >>>> find in various popular python libraries, and in some it is actually >>>> enforced. For example, I do quite a bit of work with classifiers using the >>>> sklearn estimator API, and for various reasons sklearn enforce this pattern >>>> for an __init__ (see here >>>> <https://scikit-learn.org/stable/developers/develop.html#instantiation> >>>> if interested). >>>> >>>> Here is an example of this pattern from the standard library (from >>>> textwrap.TextWrapper): >>>> ``` >>>> def __init__(self, >>>> width=70, >>>> initial_indent="", >>>> subsequent_indent="", >>>> expand_tabs=True, >>>> replace_whitespace=True, >>>> fix_sentence_endings=False, >>>> break_long_words=True, >>>> drop_whitespace=True, >>>> break_on_hyphens=True, >>>> tabsize=8, >>>> *, >>>> max_lines=None, >>>> placeholder=' [...]'): >>>> self.width = width >>>> self.initial_indent = initial_indent >>>> self.subsequent_indent = subsequent_indent >>>> self.expand_tabs = expand_tabs >>>> self.replace_whitespace = replace_whitespace >>>> self.fix_sentence_endings = fix_sentence_endings >>>> self.break_long_words = break_long_words >>>> self.drop_whitespace = drop_whitespace >>>> self.break_on_hyphens = break_on_hyphens >>>> self.tabsize = tabsize >>>> self.max_lines = max_lines >>>> self.placeholder = placeholder >>>> ``` >>>> >>>> With a quick scan of the top 50 or so most used python packages, *1 in >>>> 4* __init__ methods that takes arguments has the line `self.argument_i >>>> = argument_i` for every single argument, with several of them having 10+ >>>> arguments. >>>> >>>> *Suggestion:* >>>> >>>> A new built-in called something like `assign()` which would assign >>>> every single __init__ arg to a corresponding attribute. e.g. the snippet >>>> from above could be rewritten to: >>>> ``` >>>> def __init__(self, argument_1, argument_2, argument_3=None): >>>> assign() >>>> # other init logic goes here >>>> ``` >>>> >>>> This could alternatively be implemented as a decorator, like so >>>> ``` >>>> @assign >>>> def __init__(self, argument_1, argument_2, argument_3=None): >>>> # other init logic goes here >>>> ``` >>>> but then this requires a `pass` if no other logic is needed inside the >>>> __init__. There may also be some other syntax for this which would be even >>>> easier to use. >>>> >>>> Is this something that others would find useful? >>>> >>>> Thanks, >>>> >>>> Lewis >>>> _______________________________________________ >>>> Python-ideas mailing list -- python-ideas@python.org >>>> To unsubscribe send an email to python-ideas-le...@python.org >>>> https://mail.python.org/mailman3/lists/python-ideas.python.org/ >>>> Message archived at >>>> https://mail.python.org/archives/list/python-ideas@python.org/message/VLI3DOFA5VWMGJMJGRDC7JZTRKEPPZNU/ >>>> Code of Conduct: http://python.org/psf/codeofconduct/ >>>> >>> _______________________________________________ >> Python-ideas mailing list -- python-ideas@python.org >> To unsubscribe send an email to python-ideas-le...@python.org >> https://mail.python.org/mailman3/lists/python-ideas.python.org/ >> Message archived at >> https://mail.python.org/archives/list/python-ideas@python.org/message/SCTXSEKOWDRDGVXXOEB7JUC6WE7XKGMO/ >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/3QY6NIT7Y37PHKCYGJXJAONS35E3YZWH/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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