On Sat, Aug 29, 2020 at 07:22:52PM +0100, Paul Moore wrote: > > Item assignment (ie __setitem__) is the one thing that a function call > > can't do. If we want keywords in our __getitem__ and so on commands, then > > one route for item assignment is to allow > > >>> d[1, 2, a=3, b=4] = 5 > > as valid syntax. > > Again, obvious. But you still haven't given any reason why we would > want to do that.
See the PEP: https://www.python.org/dev/peps/pep-0472/ although I think we can eliminate a couple of the use-cases from contention, such as changes to built-in dicts and lists. For example, consider the case where we might have named axes (I think it is Todd who wants this for xarray). We want to be able to use the same notation for getters, setters and deleters. I don't know the axis names xarray uses, so I'm going to make them up: If you can use subscripting to get an axis: obj[7:87:3, axis='widdershins'] then you ought to be able to use subscripting to set or delete an axis: obj[15::9, axis='hubwise'] del obj[2:5, axis='turnwise'] (Users of xarray may be able to suggest some more realist examples.) I expect pandas could use this too. I would love to be able to do this in a matrix: # standard element access notation matrix[2, 3] = 2.5 # delete an entire column del matrix[column=4] # and replace an entire row matrix[row=3] = [1.5, 2.5, 3.5, 4.5, 6.5] Of course we could use named getter, setter and deleter methods for this, but subscript syntax is a succinct notation which comes very close to the standard notation used in the relevant domains. The bottom line here is that if your operations come in sets of three, for getting, setting and deleting a specific sub-element (a row, a column, item, key, etc.) then subscript syntax is a more natural notation than separate getter/setter/deleter methods. Even if your object is immutable and so only the getter is defined, it's still more natural to use subscript notation. -- Steve _______________________________________________ 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/ZWS3OUX7DPMYG2YK2MACDRCA777CWCIM/ Code of Conduct: http://python.org/psf/codeofconduct/
