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bpo-25652: Fix __rmod__ of UserString #13326

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Merged
miss-islington merged 5 commits into from
May 21, 2019
Merged

bpo-25652: Fix __rmod__ of UserString #13326

miss-islington merged 5 commits into from
May 21, 2019

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@isidentical
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@isidentical isidentical commented May 14, 2019 •
edited by gvanrossum
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The __rmod__ method of collections.UserString class had a bug that made it unusable.

https://bugs.python.org/issue25652

@isidentical isidentical requested a review from rhettinger as a code owner May 14, 2019 18:41
@isidentical isidentical changed the title Remove __rmod__ of UserString bpo-25652: Remove __rmod__ of UserString May 14, 2019
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jcgoble3 commented May 14, 2019

As the person who originally filed the bpo issue, I stand by my statement that it's better to fix the bug rather than just remove the method. As demonstrated by my userstringerror.py attachment on the issue, a subclass of a subclass of UserString can be bitten by this due to Python allowing a subclass to override a dunder of the parent class, even when the subclass object is the right-hand operand. (For example, the sub-subclass may be for a specialized case where pre-processing or normalization is required before formatting.)

Therefore __rmod__ is useful, and removing it would force subclass authors to write the implementation themselves rather than extending the UserString method..

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isidentical commented May 14, 2019 •
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@rhettinger whats your thought?

I agree with @jcgoble3

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gvanrossum commented May 20, 2019

Yeah, let's fix the bug and add a test.

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isidentical commented May 21, 2019

Fixed and tested.

@gvanrossum gvanrossum changed the title bpo-25652: Remove __rmod__ of UserString bpo-25652: Fix __rmod__ of UserString May 21, 2019
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gvanrossum reviewed May 21, 2019
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Lib/test/test_collections.py Outdated
arg = UserString("python")
template = "I love %s"
self.assertEqual(arg.__rmod__(template), "I love python")
self.assertIs(arg.__rmod__(type('Dummy', (), {})), NotImplemented)
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@gvanrossum gvanrossum May 21, 2019

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It would be more convincing if the test reproduced the end-to-end example from the bpo issue (https://bugs.python.org/file46854/userstringerror.py).

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@isidentical isidentical May 21, 2019

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Okey, done.

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gvanrossum reviewed May 21, 2019
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OK, there's one whitespace nit in the new test left.

Lib/test/test_collections.py Outdated
def test_str_rmod(self):
class ustr2(UserString):
pass

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@gvanrossum gvanrossum May 21, 2019

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Drop the extra blank line please.

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@isidentical isidentical May 21, 2019

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Ah, sorry for that. Fixed

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jcgoble3 commented May 21, 2019

Do the new tests belong in test_collections.py or test_userstring.py? I'm also confused as to why the three test_user*.py files exist when test_collections.py also has tests for those classes.

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isidentical commented May 21, 2019

I wasn't aware of these tests. Should i move the test?

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jcgoble3 commented May 21, 2019

I'm still new to the contributing process, so I will let the core devs figure out where they belong. I honestly don't know, hence why I asked it as a neutral question.

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gvanrossum commented May 21, 2019

Looks like the tests in test_collections.py only make very little mention of UserString etc., and the important tests for those classes are in their own test file. So I recommend moving the new tests to test_userstring.py.

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isidentical commented May 21, 2019

I moved the test.

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gvanrossum approved these changes May 21, 2019
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OK, if the test pass it will be merged. Thanks!

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isidentical commented May 21, 2019

Thank you for reviewing it.

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miss-islington commented May 21, 2019

@isidentical: Status check is done, and it's a success ✅ .

@miss-islington miss-islington merged commit 7abf8c6 into python:master May 21, 2019
@isidentical isidentical deleted the issue25652 branch December 7, 2019 12:09
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@gvanrossum gvanrossum gvanrossum approved these changes

@rhettinger rhettinger Awaiting requested review from rhettinger

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@isidentical @jcgoble3 @gvanrossum @miss-islington @the-knights-who-say-ni @bedevere-bot