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 <lrjball@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-leave@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/VLI3DO... Code of Conduct: http://python.org/psf/codeofconduct/