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Bad f-string, causing CI issues

fanninpm

Feature

Toy Example (adapted from extra_tests/snippets/fstrings.py, lines 47-48)

Code

foo = "bar"
part_spec = ">+#10x"
print(f"{16:0{part_spec}}{foo}")

CPython

RustPython

SyntaxError: Got error in f-string: Invalid expression: invalid syntax. Got unexpected token 'part_spec' at line 1 column 9
print(f"{16:0{part_spec}}{foo}")
        ^

Real-world Example (adapted from CPython 3.9's Lib/test/test_fstring.py, lines 581-584)

Code

import decimal
width = 10
precision = 4
value = decimal.Decimal('12.34567')
print(f'result: {value:{width}.{precision}}')

CPython

RustPython

SyntaxError: Got error in f-string: Invalid expression: invalid syntax. Got unexpected token '{' at line 1 column 9
print(f'result: {value:{width}.{precision}}')
        ^

Python Documentation

https://docs.python.org/3/reference/lexical_analysis.html#grammar-token-python-grammar-format_spec

@coolreader18 this has been plaguing the CI for the past day or so (because of the --install-pip step).