Message318547
Currently f-strings are a bit of a hack. They certainly work very well for users, but they are implemented in ast.c and therefore not part of the Python grammar and the tokenizer.
I want to change this. I wrote an alternative implementation of f-strings in parso (http://parso.readthedocs.io/en/latest/). The idea I have is to modify the Python grammar slightly (https://github.com/davidhalter/parso/blob/master/parso/python/grammar37.txt#L149):
fstring: FSTRING_START fstring_content* FSTRING_END
fstring_content: FSTRING_STRING | fstring_expr
fstring_conversion: '!' NAME
fstring_expr: '{' testlist [ fstring_conversion ] [ fstring_format_spec ] '}'
fstring_format_spec: ':' fstring_content*
We would push most of the hard work to the tokenizer. This obviously means that we have to add a lot of code there. I wrote a tokenizer in Python for parso here: in https://github.com/davidhalter/parso/blob/master/parso/python/tokenize.py. It is definitely working well. The biggest difference to the current tokenizer.c is that you have to work with stacks and be way more context-sensitive.
There were attempts to change the Grammar of f-strings like https://www.python.org/dev/peps/pep-0536/. It hasn't caught on, because it tried to change the semantics of f-strings. The implementation in parso has not changed the semantics of f-strings.
In a first step I would like to get this working for CPython and not tokenize.py. Modifying tokenize.py will not be part of my initial work here.
I have discussed this with Łukasz Langa, so if you guys have no objections I will start working on it. Please let me know if you support this or not. |
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Date |
User |
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2018-06-03 12:59:38 | davidhalter | set | recipients:
+ davidhalter |
2018-06-03 12:59:38 | davidhalter | set | messageid: <1528030778.27.0.592728768989.issue33754@psf.upfronthosting.co.za> |
2018-06-03 12:59:38 | davidhalter | link | issue33754 messages |
2018-06-03 12:59:38 | davidhalter | create | |
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