python3: f-string causes "Bear YapfBear failed"

[Pajinek]

Traceback when new format of f-string is used in Python 3: version 0.12.0.dev99999999999999

Example:

example = "hello"
str = f"{example}"  

  File "/coala/coalib/bears/Bear.py", line 282, in execute
    return [] if result is None else list(result)
  File "/coala-bears/bears/python/YapfBear.py", line 155, in run
    ''.join(file), style_config=fname)[0].splitlines(True)
  File "/usr/lib/python3.6/site-packages/yapf/yapflib/yapf_api.py", line 126, in FormatCode
    tree = pytree_utils.ParseCodeToTree(unformatted_source)
  File "/usr/lib/python3.6/site-packages/yapf/yapflib/pytree_utils.py", line 108, in ParseCodeToTree
    tree = parser_driver.parse_string(code, debug=False)
  File "/usr/lib64/python3.6/lib2to3/pgen2/driver.py", line 106, in parse_string
    return self.parse_tokens(tokens, debug)
  File "/usr/lib64/python3.6/lib2to3/pgen2/driver.py", line 71, in parse_tokens
    if p.addtoken(type, value, (prefix, start)):
  File "/usr/lib64/python3.6/lib2to3/pgen2/parse.py", line 159, in addtoken
    raise ParseError("bad input", type, value, context)
lib2to3.pgen2.parse.ParseError: bad input: type=3, value='"www.{HOSTNAME}"', context=('', (20, 28))
Executing section all.python.docs...

[SanketDG]

f-strings are available from python version 3.6, what version are you using?

[Pajinek]

My code is written in Python 3.7. And I use for check coala by docker image:

docker run -ti --rm -v '${CURDIR}:/app:Z' -w /app coala/base coala -an

[cathlinlord]

As part of a computer science course, my team and I are working towards contributing to open source code. If possible, we would like to work on this issue. Thanks!

[stephensonc]

@Pajinek, I am a member of the team that @cathlinlord mentioned and have been investigating this issue. It would seem as though the issue stems from the lib2to3 module of python 3.6 not parsing f-strings correctly as documented here.

It is using the 3.6 version of lib2to3 because the docker base image on DockerHub is outdated. The dockerfile in the docker-coala-base repository is set to use python 3.6. Part of the difficulty in updating the dockerfile stems from OpenSUSE Tumbleweed no longer containing/supporting the binary for python 3.6, as seen here.

[Fusion-Pie]

Hey! I will really like to work on this issue. I will try my best to solve this issue if I get assigned to it. Thank you

[abhishalya]

@Fusion-Pie No assignment required, feel free to work on this :)