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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>
This commit is contained in:
Jim Mussared 2021-08-13 01:44:08 +10:00 committed by Damien George
parent 162bf3c5d8
commit 692d36d779
18 changed files with 292 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
mpy-cross/mpconfigport.h
View File

@ -76,6 +76,7 @@
#define MICROPY_CPYTHON_COMPAT (1)
#define MICROPY_USE_INTERNAL_PRINTF (0)
#define MICROPY_PY_FSTRINGS (1)
#define MICROPY_PY_BUILTINS_STR_UNICODE (1)
#if !(defined(MICROPY_GCREGS_SETJMP) || defined(__x86_64__) || defined(__i386__) || defined(__thumb2__) || defined(__thumb__) || defined(__arm__))

1
ports/unix/mpconfigport.h
View File

@ -88,6 +88,7 @@
#define MICROPY_PY_FUNCTION_ATTRS (1)
#define MICROPY_PY_DESCRIPTORS (1)
#define MICROPY_PY_DELATTR_SETATTR (1)
#define MICROPY_PY_FSTRINGS (1)
#define MICROPY_PY_BUILTINS_STR_UNICODE (1)
#define MICROPY_PY_BUILTINS_STR_CENTER (1)
#define MICROPY_PY_BUILTINS_STR_PARTITION (1)

1
ports/windows/mpconfigport.h
View File

@ -66,6 +66,7 @@
#define MICROPY_PY_FUNCTION_ATTRS (1)
#define MICROPY_PY_DESCRIPTORS (1)
#define MICROPY_PY_DELATTR_SETATTR (1)
#define MICROPY_PY_FSTRINGS (1)
#define MICROPY_PY_BUILTINS_STR_UNICODE (1)
#define MICROPY_PY_BUILTINS_STR_CENTER (1)
#define MICROPY_PY_BUILTINS_STR_PARTITION (1)

128
py/lexer.c
View File

@ -62,6 +62,12 @@ STATIC bool is_char_or3(mp_lexer_t *lex, byte c1, byte c2, byte c3) {
return lex->chr0 == c1 || lex->chr0 == c2 || lex->chr0 == c3;
}
#if MICROPY_PY_FSTRINGS
STATIC bool is_char_or4(mp_lexer_t *lex, byte c1, byte c2, byte c3, byte c4) {
return lex->chr0 == c1 || lex->chr0 == c2 || lex->chr0 == c3 || lex->chr0 == c4;
}
#endif
STATIC bool is_char_following(mp_lexer_t *lex, byte c) {
return lex->chr1 == c;
}
@ -105,7 +111,13 @@ STATIC bool is_following_odigit(mp_lexer_t *lex) {
STATIC bool is_string_or_bytes(mp_lexer_t *lex) {
return is_char_or(lex, '\'', '\"')
#if MICROPY_PY_FSTRINGS
|| (is_char_or4(lex, 'r', 'u', 'b', 'f') && is_char_following_or(lex, '\'', '\"'))
|| (((is_char_and(lex, 'r', 'f') || is_char_and(lex, 'f', 'r'))
&& is_char_following_following_or(lex, '\'', '\"')))
#else
|| (is_char_or3(lex, 'r', 'u', 'b') && is_char_following_or(lex, '\'', '\"'))
#endif
|| ((is_char_and(lex, 'r', 'b') || is_char_and(lex, 'b', 'r'))
&& is_char_following_following_or(lex, '\'', '\"'));
}
@ -132,9 +144,35 @@ STATIC void next_char(mp_lexer_t *lex) {
++lex->column;
}
// shift the input queue forward
lex->chr0 = lex->chr1;
lex->chr1 = lex->chr2;
lex->chr2 = lex->reader.readbyte(lex->reader.data);
// and add the next byte from either the fstring args or the reader
#if MICROPY_PY_FSTRINGS
if (lex->fstring_args_idx) {
// if there are saved chars, then we're currently injecting fstring args
if (lex->fstring_args_idx < lex->fstring_args.len) {
lex->chr2 = lex->fstring_args.buf[lex->fstring_args_idx++];
} else {
// no more fstring arg bytes
lex->chr2 = '\0';
}
if (lex->chr0 == '\0') {
// consumed all fstring data, restore saved input queue
lex->chr0 = lex->chr0_saved;
lex->chr1 = lex->chr1_saved;
lex->chr2 = lex->chr2_saved;
// stop consuming fstring arg data
vstr_reset(&lex->fstring_args);
lex->fstring_args_idx = 0;
}
} else
#endif
{
lex->chr2 = lex->reader.readbyte(lex->reader.data);
}
if (lex->chr1 == '\r') {
// CR is a new line, converted to LF
@ -272,7 +310,7 @@ STATIC bool get_hex(mp_lexer_t *lex, size_t num_digits, mp_uint_t *result) {
return true;
}
STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw) {
STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw, bool is_fstring) {
// get first quoting character
char quote_char = '\'';
if (is_char(lex, '\"')) {
@ -293,12 +331,57 @@ STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw) {
}
size_t n_closing = 0;
#if MICROPY_PY_FSTRINGS
if (is_fstring) {
// assume there's going to be interpolation, so prep the injection data
// fstring_args_idx==0 && len(fstring_args)>0 means we're extracting the args.
// only when fstring_args_idx>0 will we consume the arg data
// note: lex->fstring_args will be empty already (it's reset when finished)
vstr_add_str(&lex->fstring_args, ".format(");
}
#endif
while (!is_end(lex) && (num_quotes > 1 || !is_char(lex, '\n')) && n_closing < num_quotes) {
if (is_char(lex, quote_char)) {
n_closing += 1;
vstr_add_char(&lex->vstr, CUR_CHAR(lex));
} else {
n_closing = 0;
#if MICROPY_PY_FSTRINGS
while (is_fstring && is_char(lex, '{')) {
next_char(lex);
if (is_char(lex, '{')) {
// "{{" is passed through unchanged to be handled by str.format
vstr_add_byte(&lex->vstr, '{');
next_char(lex);
} else {
// remember the start of this argument (if we need it for f'{a=}').
size_t i = lex->fstring_args.len;
// extract characters inside the { until we reach the
// format specifier or closing }.
// (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, ':', '}')) {
// like the default case at the end of this function, stay 8-bit clean
vstr_add_byte(&lex->fstring_args, CUR_CHAR(lex));
next_char(lex);
}
if (lex->fstring_args.buf[lex->fstring_args.len - 1] == '=') {
// if the last character of the arg was '=', then inject "arg=" before the '{'.
// f'{a=}' --> 'a={}'.format(a)
vstr_add_strn(&lex->vstr, lex->fstring_args.buf + i, lex->fstring_args.len - i);
// remove the trailing '='
lex->fstring_args.len--;
}
// comma-separate args
vstr_add_byte(&lex->fstring_args, ',');
}
vstr_add_byte(&lex->vstr, '{');
}
#endif
if (is_char(lex, '\\')) {
next_char(lex);
unichar c = CUR_CHAR(lex);
@ -451,6 +534,23 @@ STATIC bool skip_whitespace(mp_lexer_t *lex, bool stop_at_newline) {
}
void mp_lexer_to_next(mp_lexer_t *lex) {
#if MICROPY_PY_FSTRINGS
if (lex->fstring_args.len && lex->fstring_args_idx == 0) {
// moving onto the next token means the literal string is complete.
// switch into injecting the format args.
vstr_add_byte(&lex->fstring_args, ')');
lex->chr0_saved = lex->chr0;
lex->chr1_saved = lex->chr1;
lex->chr2_saved = lex->chr2;
lex->chr0 = lex->fstring_args.buf[0];
lex->chr1 = lex->fstring_args.buf[1];
lex->chr2 = lex->fstring_args.buf[2];
// we've already extracted 3 chars, but setting this non-zero also
// means we'll start consuming the fstring data
lex->fstring_args_idx = 3;
}
#endif
// start new token text
vstr_reset(&lex->vstr);
@ -506,6 +606,7 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
do {
// parse type codes
bool is_raw = false;
bool is_fstring = false;
mp_token_kind_t kind = MP_TOKEN_STRING;
int n_char = 0;
if (is_char(lex, 'u')) {
@ -524,7 +625,25 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
kind = MP_TOKEN_BYTES;
n_char = 2;
}
#if MICROPY_PY_FSTRINGS
if (is_char_following(lex, 'f')) {
// raw-f-strings unsupported, immediately return (invalid) token.
lex->tok_kind = MP_TOKEN_FSTRING_RAW;
break;
}
#endif
}
#if MICROPY_PY_FSTRINGS
else if (is_char(lex, 'f')) {
if (is_char_following(lex, 'r')) {
// raw-f-strings unsupported, immediately return (invalid) token.
lex->tok_kind = MP_TOKEN_FSTRING_RAW;
break;
}
n_char = 1;
is_fstring = true;
}
#endif
// Set or check token kind
if (lex->tok_kind == MP_TOKEN_END) {
@ -543,7 +662,7 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
}
// Parse the literal
parse_string_literal(lex, is_raw);
parse_string_literal(lex, is_raw, is_fstring);
// Skip whitespace so we can check if there's another string following
skip_whitespace(lex, true);
@ -703,6 +822,9 @@ mp_lexer_t *mp_lexer_new(qstr src_name, mp_reader_t reader) {
lex->num_indent_level = 1;
lex->indent_level = m_new(uint16_t, lex->alloc_indent_level);
vstr_init(&lex->vstr, 32);
#if MICROPY_PY_FSTRINGS
vstr_init(&lex->fstring_args, 0);
#endif
// store sentinel for first indentation level
lex->indent_level[0] = 0;

11
py/lexer.h
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@ -44,6 +44,10 @@ typedef enum _mp_token_kind_t {
MP_TOKEN_INVALID,
MP_TOKEN_DEDENT_MISMATCH,
MP_TOKEN_LONELY_STRING_OPEN,
#if MICROPY_PY_FSTRINGS
MP_TOKEN_MALFORMED_FSTRING,
MP_TOKEN_FSTRING_RAW,
#endif
MP_TOKEN_NEWLINE,
MP_TOKEN_INDENT,
@ -158,6 +162,9 @@ typedef struct _mp_lexer_t {
mp_reader_t reader; // stream source
unichar chr0, chr1, chr2; // current cached characters from source
#if MICROPY_PY_FSTRINGS
unichar chr0_saved, chr1_saved, chr2_saved; // current cached characters from alt source
#endif
size_t line; // current source line
size_t column; // current source column
@ -173,6 +180,10 @@ typedef struct _mp_lexer_t {
size_t tok_column; // token source column
mp_token_kind_t tok_kind; // token kind
vstr_t vstr; // token data
#if MICROPY_PY_FSTRINGS
vstr_t fstring_args; // extracted arguments to pass to .format()
size_t fstring_args_idx; // how many bytes of fstring_args have been read
#endif
} mp_lexer_t;
mp_lexer_t *mp_lexer_new(qstr src_name, mp_reader_t reader);

5
py/mpconfig.h
View File

@ -875,6 +875,11 @@ typedef double mp_float_t;
#define MICROPY_PY_ASYNC_AWAIT (1)
#endif
// Support for literal string interpolation, f-strings (see PEP 498, Python 3.6+)
#ifndef MICROPY_PY_FSTRINGS
#define MICROPY_PY_FSTRINGS (0)
#endif
// Support for assignment expressions with := (see PEP 572, Python 3.8+)
#ifndef MICROPY_PY_ASSIGN_EXPR
#define MICROPY_PY_ASSIGN_EXPR (1)

8
py/parse.c
View File

@ -1152,6 +1152,14 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
} else if (lex->tok_kind == MP_TOKEN_DEDENT_MISMATCH) {
exc = mp_obj_new_exception_msg(&mp_type_IndentationError,
MP_ERROR_TEXT("unindent doesn't match any outer indent level"));
#if MICROPY_PY_FSTRINGS
} else if (lex->tok_kind == MP_TOKEN_MALFORMED_FSTRING) {
exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
MP_ERROR_TEXT("malformed f-string"));
} else if (lex->tok_kind == MP_TOKEN_FSTRING_RAW) {
exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
MP_ERROR_TEXT("raw f-strings are not supported"));
#endif
} else {
exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
MP_ERROR_TEXT("invalid syntax"));

57
tests/basics/string_fstring.py Normal file
View File

@ -0,0 +1,57 @@
def f():
return 4
def g(_):
return 5
def h():
return 6
print(f'no interpolation')
print(f"no interpolation")
print(f"""no interpolation""")
x, y = 1, 2
print(f'{x}')
print(f'{x:08x}')
print(f'{x=}')
print(f'{x=:08x}')
print(f'a {x} b {y} c')
print(f'a {x:08x} b {y} c')
print(f'a {x=} b {y} c')
print(f'a {x=:08x} b {y} c')
print(f'a {"hello"} b')
print(f'a {f() + g("foo") + h()} b')
print(f'a {f() + g("foo") + h()=} b')
print(f'a {f() + g("foo") + h()=:08x} b')
def foo(a, b):
return f'{x}{y}{a}{b}'
print(foo(7, 8))
# PEP-0498 specifies that '\\' and '#' must be disallowed explicitly, whereas
# MicroPython relies on the syntax error as a result of the substitution.
print(f"\\")
print(f'#')
try:
eval("f'{\}'")
except SyntaxError:
print('SyntaxError')
try:
eval("f'{#}'")
except SyntaxError:
print('SyntaxError')
# PEP-0498 specifies that handling of double braces '{{' or '}}' should
# behave like str.format.
print(f'{{}}')
print(f'{{{4*10}}}', '{40}')
# A single closing brace, unlike str.format should raise a syntax error.
# MicroPython instead raises ValueError at runtime from the substitution.
try:
eval("f'{{}'")
except (ValueError, SyntaxError):
# MicroPython incorrectly raises ValueError here.
print('SyntaxError')

1
tests/cmdline/cmd_parsetree.py
View File

@ -10,3 +10,4 @@ d = b"bytes"
e = b"a very long bytes that will not be interned"
f = 123456789012345678901234567890
g = 123
h = f"fstring: '{b}'"

26
tests/cmdline/cmd_parsetree.py.exp
View File

@ -1,6 +1,6 @@
----------------
[ 4] \(rule\|file_input_2\)(1) (n=9)
tok(4)
[ 4] \(rule\|file_input_2\)(1) (n=10)
tok(6)
[ 4] \(rule\|for_stmt\)(22) (n=4)
id(i)
[ 4] \(rule\|atom_paren\)(45) (n=1)
@ -9,7 +9,7 @@
NULL
[ 6] \(rule\|expr_stmt\)(5) (n=2)
id(a)
tok(14)
tok(16)
[ 7] \(rule\|expr_stmt\)(5) (n=2)
id(b)
str(str)
@ -28,6 +28,16 @@
[ 12] \(rule\|expr_stmt\)(5) (n=2)
id(g)
int(123)
[ 13] \(rule\|expr_stmt\)(5) (n=2)
id(h)
[ 13] \(rule\|atom_expr_normal\)(44) (n=2)
[ 13] literal const(\.\+)
[ 13] \(rule\|atom_expr_trailers\)(142) (n=2)
[ 13] \(rule\|trailer_period\)(50) (n=1)
id(format)
[ 13] \(rule\|trailer_paren\)(48) (n=1)
[ 13] \(rule\|arglist\)(164) (n=1)
id(b)
----------------
File cmdline/cmd_parsetree.py, code block '<module>' (descriptor: \.\+, bytecode @\.\+ bytes)
Raw bytecode (code_info_size=\\d\+, bytecode_size=\\d\+):
@ -46,6 +56,7 @@ arg names:
bc=32 line=10
bc=37 line=11
bc=42 line=12
bc=48 line=13
00 BUILD_TUPLE 0
02 GET_ITER_STACK
03 FOR_ITER 12
@ -65,8 +76,13 @@ arg names:
39 STORE_NAME f
42 LOAD_CONST_SMALL_INT 123
45 STORE_NAME g
48 LOAD_CONST_NONE
49 RETURN_VALUE
48 LOAD_CONST_OBJ \.\+
50 LOAD_METHOD format
53 LOAD_NAME b (cache=0)
57 CALL_METHOD n=1 nkw=0
59 STORE_NAME h
62 LOAD_CONST_NONE
63 RETURN_VALUE
mem: total=\\d\+, current=\\d\+, peak=\\d\+
stack: \\d\+ out of \\d\+
GC: total: \\d\+, used: \\d\+, free: \\d\+

12
tests/cpydiff/core_fstring_concat.py Normal file
View File

@ -0,0 +1,12 @@
"""
categories: Core
description: f-strings don't support concatenation with adjacent literals if the adjacent literals contain braces
cause: MicroPython is optimised for code space.
workaround: Use the + operator between literal strings when either is an f-string
"""
x = 1
print("aa" f"{x}")
print(f"{x}" "ab")
print("a{}a" f"{x}")
print(f"{x}" "a{}b")

9
tests/cpydiff/core_fstring_parser.py Normal file
View File

@ -0,0 +1,9 @@
"""
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({})}"

8
tests/cpydiff/core_fstring_raw.py Normal file
View File

@ -0,0 +1,8 @@
"""
categories: Core
description: Raw f-strings are not supported
cause: MicroPython is optimised for code space.
workaround: Unknown
"""
rf"hello"

18
tests/cpydiff/core_fstring_repr.py Normal file
View File

@ -0,0 +1,18 @@
"""
categories: Core
description: f-strings don't support the !r, !s, and !a conversions
cause: MicroPython is optimised for code space.
workaround: Use repr(), str(), and ascii() explictly.
"""
class X:
def __repr__(self):
return "repr"
def __str__(self):
return "str"
print(f"{X()!r}")
print(f"{X()!s}")

3
tests/feature_check/fstring.py Normal file
View File

@ -0,0 +1,3 @@
# check whether f-strings (PEP-498) are supported
a = 1
print(f"a={a}")

1
tests/feature_check/fstring.py.exp Normal file
View File

@ -0,0 +1 @@
a=1

8
tests/run-tests.py
View File

@ -290,6 +290,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
skip_const = False
skip_revops = False
skip_io_module = False
skip_fstring = False
skip_endian = False
has_complex = True
has_coverage = False
@ -348,6 +349,11 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
if output != b"uio\n":
skip_io_module = True
# Check if fstring feature is enabled, and skip such tests if it doesn't
output = run_feature_check(pyb, args, base_path, "fstring.py")
if output != b"a=1\n":
skip_fstring = True
# Check if emacs repl is supported, and skip such tests if it's not
t = run_feature_check(pyb, args, base_path, "repl_emacs_check.py")
if "True" not in str(t, "ascii"):
@ -543,6 +549,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
is_async = test_name.startswith(("async_", "uasyncio_"))
is_const = test_name.startswith("const")
is_io_module = test_name.startswith("io_")
is_fstring = test_name.startswith("string_fstring")
skip_it = test_file in skip_tests
skip_it |= skip_native and is_native
@ -555,6 +562,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
skip_it |= skip_const and is_const
skip_it |= skip_revops and "reverse_op" in test_name
skip_it |= skip_io_module and is_io_module
skip_it |= skip_fstring and is_fstring
if args.list_tests:
if not skip_it:

2
tools/tinytest-codegen.py
View File

@ -99,6 +99,8 @@ exclude_tests = (
"misc/sys_settrace_loop.py",
"misc/sys_settrace_generator.py",
"misc/sys_settrace_features.py",
# don't have f-string
"basics/string_fstring.py",
)
output = []