Hi all, The Programming Recommendations section in PEP-8 states
"For sequences, (strings, lists, tuples), use the fact that empty sequences are false:" # Correct: if not seq: if seq: # Wrong: if len(seq): if not len(seq): In the talk "When Python Practices Go Wrong" Brandon Rhodes makes a good point against this practice based on "explicit is better than implicit" (https://youtu.be/S0No2zSJmks?t=873). He advertizes using if len(seq): While that is as explicit as one can get within the current language, it could still be more explicit: Semantically, we're not interested in the (zero) length of the sequence, but want to know if it is empty. **Proposal** Therefore, I propose syntax for an explicit empty check if isempty(seq): (i) or if seq.is_empty() (ii) This proposal is mainly motivated by the Zen verses "Explicit is better than implicit" and "Readability counts". The two variants have slightly different advantages and disadvantages: (i) would add an __isempty__ protocol and a corresponding isempty() builtin function. One could argue that this is somewhat redundant with __len__. However, this is a typical pattern in collection.abc abstract base classes: There are only a few abstract methods and futher concepts are added as mixin methods (which are by default implemented using the abstract methods). https://docs.python.org/3/library/collections.abc.html#collections-abstract-base-classes (ii) would alternatively only implement a method on the collection. There's also precedence for predefined methods on collections, e.g. Sequence.index(). Advantages over the protocol approach are: - It's a smaller language change than adding a protocol and a builtin function - The order seq.is_empty() matches the order used in spoken english ("if the sequence is empty") which is more readable than isempty(seq). - It's tab-completable (-> usability) Disadvantages: - Emptiness is similar to length, and people might be used to the builtin-method concept for such things. - A protocol is more powerful than a method: One can support isempty() via len() even for objects that do not implement __isempty__. However, this more a theoretical advantage. I assume that in practice all collections derive from the collection.abc classes, so if the is_empty() method is implemented there, all typical use cases should be covered. I'm looking forward to your feedback! Tim _______________________________________________ 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/PBRSOAFHNT5YWKDPJKSS6SW4JA62CARC/ Code of Conduct: http://python.org/psf/codeofconduct/
