In code, list.clear doesn't throw error - it's just ignored
DFS
nospam at dfs.com
Sun Nov 13 22:23:09 EST 2022
On 11/13/2022 9:11 PM, Chris Angelico wrote:
> On Mon, 14 Nov 2022 at 11:53, DFS <nospam at dfs.com> wrote:
>>
>> On 11/13/2022 5:20 PM, Jon Ribbens wrote:
>>> On 2022-11-13, DFS <nospam at dfs.com> wrote:
>>>> In code, list.clear is just ignored.
>>>> At the terminal, list.clear shows
>>>> <built-in method clear of list object at 0x000001C9CFEC4240>
>>>>
>>>>
>>>> in code:
>>>> x = [1,2,3]
>>>> x.clear
>>>> print(len(x))
>>>> 3
>>>>
>>>> at terminal:
>>>> x = [1,2,3]
>>>> x.clear
>>>> <built-in method clear of list object at 0x000001C9CFEC4240>
>>>> print(len(x))
>>>> 3
>>>>
>>>>
>>>> Caused me an hour of frustration before I noticed list.clear() was what
>>>> I needed.
>>>>
>>>> x = [1,2,3]
>>>> x.clear()
>>>> print(len(x))
>>>> 0
>>>
>>> If you want to catch this sort of mistake automatically then you need
>>> a linter such as pylint:
>>>
>>> $ cat test.py
>>> """Create an array and print its length"""
>>>
>>> array = [1, 2, 3]
>>> array.clear
>>> print(len(array))
>>> $ pylint -s n test.py
>>> ************* Module test
>>> test.py:4:0: W0104: Statement seems to have no effect (pointless-statement)
>>
>>
>> Thanks, I should use linters more often.
>>
>> But why is it allowed in the first place?
>>
>> I stared at list.clear and surrounding code a dozen times and said
>> "Looks right! Why isn't it clearing the list?!?!"
>>
>> 2 parens later and I'm golden!
>>
>
> No part of it is invalid, so nothing causes a problem. For instance,
> you can write this:
If it wastes time like that it's invalid.
This is an easy check for the interpreter to make.
If I submit a suggestion to python-list at python.org will it just show up
here? Or do the actual Python devs intercept it?
>>>> 1
>
> And you can write this:
>
>>>> 1 + 2
>
> And you can write this:
>
>>>> print(1 + 2)
>
> But only one of those is useful in a script. Should the other two be
> errors? No. But linters WILL usually catch them, so if you have a good
> linter (especially built into your editor), you can notice these
> things.
ran pylint against it and got 0.0/10.
--disable=
invalid-name
multiple-statements
bad-indentation
line-too-long
trailing-whitespace
missing-module-docstring
missing-function-docstring
too-many-lines
fixme
and got 8.9/10.
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