On Mon, May 31, 2021 at 2:40 PM Guido van Rossum firstname.lastname@example.org wrote:
Andre, did you have an experience where something related to Ellipsis/... confused you? It is not clear to me what exactly prompted you to single out Ellipsis (or it’s repr()?)
Guido, the reason why I tried is that I am working on a project called friendly (previously named friendly-traceback) which aims to provide "easy to understand" explanations to beginners when they encounter tracebacks.
In playing with different cases involving assignments to a constant (__debug__, None, True, False, ... and Ellipsis as '...'), I came across this particular case which I thought was confusing: Python says that we cannot assign to Ellipsis ... and yet we can. I thought that the explanation provided by cPython itself could be made a bit clearer. The specific suggestion I made is based on the explanation *friendly* currently gives, where it specifies that Ellipsis refers to (...).
Admittedly, this is rather a corner case.
==== With friendly, I usually strive to cover more typical cases that are encountered by beginners, such as one example I gave at this year's PyConUS Education summit where, given the following message:
AttributeError: partially initialized module 'turtle' has no attribute 'forward' (most likely due to a circular import)
friendly adds the following "hint":
Did you give your program the same name as a Python module?
And, upon being prompted, friendly adds the following:
I suspect that you used the name turtle.py for your program and that you also wanted to import a module with the same name from Python's standard library. If so, you should use a different name for your program.
(This particular turtle is not hard-coded in friendly; any circular import is similarly analyzed and some further explanation is provided.)
 Currently, I have at least 150 different cases yielding SyntaxErrors for which friendly can provide help (see https://aroberge.github.io/friendly-traceback-docs/docs/html/syntax_tracebac... for cases covered by unit tests) and probably a hundred or so of various types of other errors. Furthermore, friendly is designed so that the explanations can be translated into other languages; currently, every case friendly covers has explanations available in both English and French.
On Mon, May 31, 2021 at 08:37 André Roberge email@example.com wrote:
On Mon, May 31, 2021 at 12:20 PM MRAB firstname.lastname@example.org wrote:
On 2021-05-31 15:55, Paul Bryan wrote:
If you're proposing prevention of monkey patching Ellipsis, I think you'll have to go all-in on all builtins.
> str = int
> str == int
If you rebind str to int, the repr of str will say <class 'int'>, so you can tell that something's happened, but the repr of ... is always 'Ellipsis', even though you've rebound Ellipsis.
Thinking some more about it, perhaps the confusion would be sufficiently reduced if the repr of '...' would be 'Ellipsis (...)', and use this repr to appear in error messages rather than simply the name Ellipsis.
On Mon, 2021-05-31 at 11:37 -0300, André Roberge wrote:
In Python `...` is referred to as `Ellipsis` and cannot be assigned
Yet, one can assign any value to the name `Ellipsis`.
Consider the following:
>>> ... Ellipsis >>> ... == Ellipsis True >>> Ellipsis Ellipsis >>> Ellipsis = 3 >>> Ellipsis 3 >>> ... = 4 File "<stdin>", line 1 ... = 4 ^ SyntaxError: cannot assign to Ellipsis >>> # But I just did assign a new value to the name Ellipsis above. >>> Ellipsis 3 >>> ... Ellipsis >>> ... == Ellipsis False
For consistency, `Ellipsis` (the name) should **always** refer to the same object that `...` refers to, so that both could not be assigned
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-- --Guido (mobile)