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py/lexer: Support nested [] and {} characters within f-string params. 

Signed-off-by: Damien George <damien@micropython.org>
This commit is contained in:
Damien George 2021-11-19 10:36:16 +11:00
parent 196d26848a
commit 11ed94797d
3 changed files with 20 additions and 6 deletions
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11
py/lexer.c
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@ -363,9 +363,16 @@ STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw, bool is_fstring)
// (MicroPython limitation) note: this is completely unaware of
// Python syntax and will not handle any expression containing '}' or ':'.
// e.g. f'{"}"}' or f'{foo({})}'.
while (!is_end(lex) && !is_char_or(lex, ':', '}')) {
unsigned int nested_bracket_level = 0;
while (!is_end(lex) && (nested_bracket_level != 0 || !is_char_or(lex, ':', '}'))) {
unichar c = CUR_CHAR(lex);
if (c == '[' || c == '{') {
nested_bracket_level += 1;
} else if (c == ']' || c == '}') {
nested_bracket_level -= 1;
}
// like the default case at the end of this function, stay 8-bit clean
vstr_add_byte(&lex->fstring_args, CUR_CHAR(lex));
vstr_add_byte(&lex->fstring_args, c);
next_char(lex);
}
if (lex->fstring_args.buf[lex->fstring_args.len - 1] == '=') {

7
tests/basics/string_fstring.py
View File

@ -22,6 +22,13 @@ def foo(a, b):
return f'{x}{y}{a}{b}'
print(foo(7, 8))
# ':' character within {...} that should not be interpreted as format specifiers.
print(f"a{[0,1,2][0:2]}")
print(f"a{[0,15,2][0:2][-1]:04x}")
# Nested '{' and '}' characters.
print(f"a{ {0,1,2}}")
# PEP-0498 specifies that '\\' and '#' must be disallowed explicitly, whereas
# MicroPython relies on the syntax error as a result of the substitution.

8
tests/cpydiff/core_fstring_parser.py
View File

@ -1,9 +1,9 @@
"""
categories: Core
description: f-strings cannot support expressions that require parsing to resolve nested braces
description: f-strings cannot support expressions that require parsing to resolve unbalanced nested braces and brackets
cause: MicroPython is optimised for code space.
workaround: Only use simple expressions inside f-strings
workaround: Always use balanced braces and brackets in expressions inside f-strings
"""
f'{"hello {} world"}'
f"{repr({})}"
print(f'{"hello { world"}')
print(f'{"hello ] world"}')