test added in gh-104067 has an fstring with an invalid escape sequence

Bug report

In response to #104049, a fix and a new test were added in #104067 and related PRs. The test in test_httpserver.py uses an fstring with an escape sequence, but does not use r:

f'listing for {self.base_url}/\?x=123'

I think the code (in two places) should be include an r: fr'listing for ...

On PyPy this is causing the test___all__.py test to fail, since it emits a warning when compiling the *.py to *.pyc. I am not sure why CPython is not seeing a similar problem. Perhaps compileall is run first? Or the warning filter captures the compilation as well as the import?

Your environment

CPython versions tested on: PyPy3.9 HEAD using stdlib 3.9.17
Operating system and architecture: any

@mattip

@mattip CPython does not issue this warning SyntaxWarning: invalid escape sequence '\?' until 3.12, though only for normal strings. What warning is PyPy3.9 emitting? (Note: try to minimize reproducing examples, as I did below ;-)

@pablogsal In 3.12 and 3.13, f-strings are not warning about invalid escapes that get warnings in real strings. This seems like a bug.

>>> f'\?'
'\\?'
>>> len(f'\?')
2
>>> '\?'
<stdin>:1: SyntaxWarning: invalid escape sequence '\?'
'\\?'

On python3.9.17 from Ubuntu, I get this

$ python3.9 -Walways -c "abc = 'abc'; print(f'listing for {abc}/\?x=123')"
<string>:1: DeprecationWarning: invalid escape sequence \?
listing for abc/\?x=123

Adding an r makes it run without a warning

$ python3.9 -Walways -c "abc = 'abc'; print(fr'listing for {abc}/\?x=123')"
listing for abc/\?x=123

@ethanfurman

Security patch #104067 was backported to 3.7, which is why it affects PyPy3.9.

@ethanfurman @JelleZijlstra Do the tests added in #104067 require invalid escapes without an 'r' prefix? Or could the escape be changed or the 'r' added?

@pablogsal

@pablogsal In 3.12 and 3.13, f-strings are not warning about invalid escapes that get warnings in real strings. This seems like a bug.

Fixed!

Thanks. I see that was backported to 3.12. I am curious why not backport it to all versions that contain the test added in #104067 (maybe excepting ones that will no longer be released)? People running the test without precompiling pyc files will see a DeprecationWarning, no?

Edit: GAA, I didn't actually look at the fix: #105800 is not what I expected.

Try as I might, I cannot get CPython3.9 to emit a DeprecationWarning in the test_httpservers.py test. So I will add the r in the PyPy port of the stdlib tests. I am not sure why the test does not emit the warning on CPython3.9, since the f-string needs an r if run outside the test, but 🤷

$ python3.9 -Walways -c "abc = 'abc'; print(f'listing for {abc}/\?x=123')"
<string>:1: DeprecationWarning: invalid escape sequence \?
listing for abc/\?x=123

Relevant: #105821

@mattip

This can be closed. @mattip An r prefix has been added in #105822.

Here it only warned/failed when bytecompile was needed, so if there wasn't a .pyc file already for test_httpservers.

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test added in gh-104067 has an fstring with an invalid escape sequence #105784

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test added in gh-104067 has an fstring with an invalid escape sequence #105784

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terryjreedy commented on Jun 14, 2023

mattip commented on Jun 14, 2023

mattip commented on Jun 14, 2023

terryjreedy commented on Jun 14, 2023

pablogsal commented on Jun 15, 2023

mattip commented on Jun 15, 2023

mattip commented on Jun 15, 2023

pablogsal commented on Jun 15, 2023

lysnikolaou commented on Jun 20, 2023

lazka commented on Jun 23, 2023

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