Currently, in `bisect` examples `grade` function is declared with mutable default for `breakpoints` arugment. I suggest updating.

https://github.com/sweeneyde commented
> I would say that even though using mutable defaults is often undesirable, there is no problem with it in this case: the body of the function does not mutate the default. It's also probably faster than re-constructing a new list at each function call. I would suggest opening an issue on https://bugs.python.org/ if you want to discuss more.

I agree that in this case it wouldn't matter because `breakpoints` are not mutated, but most of the time people copy from examples and adapt the code to their needs without giving it a second thought. In my opinion, it is a good practice to provide examples as foolproof as possible.

Another option would be to use globals:

>>> BREAKPOINTS = [60, 70, 80, 90]
>>> GRADES = "FDCBA"
>>> def grade(score):
...     i = bisect(BREAKPOINTS, score)
...     return GRADES[i]
... 
>>> [grade(score) for score in [33, 99, 77, 70, 89, 90, 100]]
['F', 'A', 'C', 'C', 'B', 'A', 'A']

It was changed from that in 2010

https://github.com/python/cpython/commit/20933e08b12b4e66c6e1baf662a679b4008d9dce

I'm going to decline this one.  It seems that you're applying a stylistic guideline to a case where it isn't needed and where it doesn't improve the example.

In this case, the example doesn't mutate the input, so the code is correct.  It has some benefit in that it communicates to the user of the function that lists are allowable as an input (which is the norm for bisect).  And the tooltips will show the relationship between the grades can the cutpoints.

Also, this isn't library code.  A bisect example needs to focus on bisect rather than other concerns.  This isn't the place to talk about the pattern of setting a default to None and then filling it in in the body of the code.  Likewise, we wouldn't use this example to communicate / and * for positional-only and keyword-only args.  Nor do we have a docstring or type signature.  Instead, it shows how to write a lookup function using bisect() and that is all we want.

Lastly, I'll note this example has been present for a long time and has proven itself effective in teaching people how bisect works.  In particular, we want to make it obvious the relationship between the 5 grades and the 4 cut points.

Understood, thanks for clarification.