On Wed, 25 Aug 2021 at 14:13, Tim Hoffmann via Python-ideas <python-ideas@python.org> wrote:
Guido van Rossum wrote:
So then the next question is, what's the use case? What code are people writing that may receive either a stdlib container or a numpy array, and which needs to do something special if there are no elements? Maybe computing the average? AFAICT Tim Hoffman (the OP) never said.
There's two parts to the answer:
1) There functions e.g. in scipy and matplotlib that accept both numpy arrays and lists of flows. Speaking from matplotlib experience: While eventually we coerce that data to a uniform internal format, there are cases in which we need to keep the original data and only convert on a lower internal level. We often can return early in a function if there is no data, which is where the emptiness check comes in. We have to take extra care to not do the PEP-8 recommended emptiness check using `if not data`.
You don't. You can write a local isempty() function in matplotlib, and add a requirement *in your own style guide* that all emptiness checks use this function. Why do people think that they can't write project-specific style guides, and everything must be in PEP 8? That baffles me.
2) Even for cases that cannot have different types in the same code, it is unsatisfactory that I have to write `if not seq` but `if len(array) == 0` depending on the expected data. IMHO whatever the recommended syntax for emptiness checking is, it should be the same for lists and arrays and dataframes.
You don't have to do any such thing. You can just write "if len(x) == 0" everywhere. No-one is *making* you write "if not seq". All I can see here is people making problems for themselves that they don't need to. Sorry if that's not how it appears to you, but I'm genuinely struggling to see why this is an issue that can't be solved by individual projects/users. The only exception I can see is the question "what's the best way to suggest to newcomers?" but that's more of a tutorial/documentation question, than one of standardisation, style guides or language features. Paul