what about a dict.setdefaults (note the s) that takes in an iterable or a dict, and uses insert-or-ignore behaviour? (unfortunately a lot of iterables and all generators are hashable, and we can't break that.)
I could really use something like that tbh.
On 2020-04-16 9:47 a.m., Alex Hall wrote:
I just tried playing with this idea:
from collections import UserDict
class InsertOrIgnoreDict(UserDict): __setitem__ = UserDict.setdefault
print(InsertOrIgnoreDict([(1, 2), (3, 4)]))
It caused an infinite chain of exceptions:
Traceback (most recent call last): File "/home/alex/.pyenv/versions/3.8.0/lib/python3.8/_collections_abc.py", line 845, in setdefault return self[key] File "/home/alex/.pyenv/versions/3.8.0/lib/python3.8/collections/__init__.py", line 1003, in __getitem__ raise KeyError(key) KeyError: 1
During handling of the above exception, another exception occurred:
Traceback (most recent call last): File "/home/alex/.pyenv/versions/3.8.0/lib/python3.8/_collections_abc.py", line 845, in setdefault return self[key] File "/home/alex/.pyenv/versions/3.8.0/lib/python3.8/collections/__init__.py", line 1003, in __getitem__ raise KeyError(key) KeyError: 1
During handling of the above exception, another exception occurred:
...
I thought that was amusing.
Anyway, one could come up with infinitely many variations of potentially useful semantics. Why include any of them in the language instead of letting users implement what they need?
On Thu, Apr 16, 2020 at 2:37 PM Soni L. <fakedme+py@gmail.com mailto:fakedme%2Bpy@gmail.com> wrote:
currently dicts have insert-or-update semantics, e.g.: >>> dict([((), 1), ((), 2)]) {(): 2} this is fine. however, in many cases insert or insert-or-ignore are more useful: (hypothetical examples) >>> InsertOrIgnoreDict([((), 1), ((), 2)]) {(): 1} >>> InsertDict([((), 1), ((), 2)]) Traceback: [...] ValueError: key exists these are useful when dealing with custom config file formats, config overrides, among other things. additionally we could also get an UpdateDict, a *view* into a dict that only allows updating existing entries: >>> a = {'a': 1} >>> b = {'a': 2, 'b': 3} >>> UpdateDict(a).update(b) >>> a {'a': 2} but I don't see an obvious usefulness to this one. it'd just be for consistency with other SQL-esque dict wrappers (like the above InsertOrIgnoreDict and InsertDict). _______________________________________________ Python-ideas mailing list -- python-ideas@python.org <mailto:python-ideas@python.org> To unsubscribe send an email to python-ideas-leave@python.org <mailto: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/7PCWDORFLBFY6HRLNNS6UBL2CRER26SM/ Code of Conduct: http://python.org/psf/codeofconduct/