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/ >> >
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