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[3.6] bpo-30529: Fix errors for invalid whitespaces in f-string subexpressions. (GH-1888) #2013

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Jun 8, 2017
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10 changes: 10 additions & 0 deletions Lib/test/test_fstring.py
Original file line number Diff line number Diff line change
Expand Up @@ -280,6 +280,10 @@ def test_missing_expression(self):
"f'{10:{ }}'",
"f' { } '",

# The Python parser ignores also the following
# whitespace characters in additional to a space.
"f'''{\t\f\r\n}'''",

# Catch the empty expression before the
# invalid conversion.
"f'{!x}'",
Expand All @@ -300,6 +304,12 @@ def test_missing_expression(self):
"f'{:x'",
])

# Different error message is raised for other whitespace characters.
self.assertAllRaise(SyntaxError, 'invalid character in identifier',
["f'''{\xa0}'''",
"\xa0",
])

def test_parens_in_expressions(self):
self.assertEqual(f'{3,}', '(3,)')

Expand Down
31 changes: 7 additions & 24 deletions Python/ast.c
Original file line number Diff line number Diff line change
Expand Up @@ -4247,49 +4247,32 @@ fstring_compile_expr(const char *expr_start, const char *expr_end,
struct compiling *c, const node *n)

{
int all_whitespace = 1;
int kind;
void *data;
PyCompilerFlags cf;
mod_ty mod;
char *str;
PyObject *o;
Py_ssize_t len;
Py_ssize_t i;
const char *s;

assert(expr_end >= expr_start);
assert(*(expr_start-1) == '{');
assert(*expr_end == '}' || *expr_end == '!' || *expr_end == ':');

/* We know there are no escapes here, because backslashes are not allowed,
and we know it's utf-8 encoded (per PEP 263). But, in order to check
that each char is not whitespace, we need to decode it to unicode.
Which is unfortunate, but such is life. */

/* If the substring is all whitespace, it's an error. We need to catch
this here, and not when we call PyParser_ASTFromString, because turning
the expression '' in to '()' would go from being invalid to valid. */
/* Note that this code says an empty string is all whitespace. That's
important. There's a test for it: f'{}'. */
o = PyUnicode_DecodeUTF8(expr_start, expr_end-expr_start, NULL);
if (o == NULL)
return NULL;
len = PyUnicode_GET_LENGTH(o);
kind = PyUnicode_KIND(o);
data = PyUnicode_DATA(o);
for (i = 0; i < len; i++) {
if (!Py_UNICODE_ISSPACE(PyUnicode_READ(kind, data, i))) {
all_whitespace = 0;
for (s = expr_start; s != expr_end; s++) {
char c = *s;
/* The Python parser ignores only the following whitespace
characters (\r already is converted to \n). */
if (!(c == ' ' || c == '\t' || c == '\n' || c == '\f')) {
break;
}
}
Py_DECREF(o);
if (all_whitespace) {
if (s == expr_end) {
ast_error(c, n, "f-string: empty expression not allowed");
return NULL;
}

/* Reuse len to be the length of the utf-8 input string. */
len = expr_end - expr_start;
/* Allocate 3 extra bytes: open paren, close paren, null byte. */
str = PyMem_RawMalloc(len + 3);
Expand Down