micropython/tests/cpydiff/core_fstring_parser.py

"""
categories: Core
description: f-strings cannot support expressions that require parsing to resolve nested braces
cause: MicroPython is optimised for code space.
workaround: Only use simple expressions inside f-strings
"""

f'{"hello {} world"}'
f"{repr({})}"
py: Implement partial PEP-498 (f-string) support. This implements (most of) the PEP-498 spec for f-strings and is based on https://github.com/micropython/micropython/pull/4998 by @klardotsh. It is implemented in the lexer as a syntax translation to `str.format`: f"{a}" --> "{}".format(a) It also supports: f"{a=}" --> "a={}".format(a) This is done by extracting the arguments into a temporary vstr buffer, then after the string has been tokenized, the lexer input queue is saved and the contents of the temporary vstr buffer are injected into the lexer instead. There are four main limitations: - raw f-strings (`fr` or `rf` prefixes) are not supported and will raise `SyntaxError: raw f-strings are not supported`. - literal concatenation of f-strings with adjacent strings will fail "{}" f"{a}" --> "{}{}".format(a) (str.format will incorrectly use the braces from the non-f-string) f"{a}" f"{a}" --> "{}".format(a) "{}".format(a) (cannot concatenate) - PEP-498 requires the full parser to understand the interpolated argument, however because this entirely runs in the lexer it cannot resolve nested braces in expressions like f"{'}'}" - The !r, !s, and !a conversions are not supported. Includes tests and cpydiffs. Signed-off-by: Jim Mussared <jim.mussared@gmail.com> 2021-08-12 16:44:08 +01:00			`"""`
			`categories: Core`
			`description: f-strings cannot support expressions that require parsing to resolve nested braces`
			`cause: MicroPython is optimised for code space.`
			`workaround: Only use simple expressions inside f-strings`
			`"""`

			`f'{"hello {} world"}'`
			`f"{repr({})}"`