bpo-36817: Add f-string debugging using '='. (GH-13123)
If a "=" is specified a the end of an f-string expression, the f-string will evaluate to the text of the expression, followed by '=', followed by the repr of the value of the expression.
diff --git a/Python/ast.c b/Python/ast.c
index 4687f81..21abd7e 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -4854,7 +4854,8 @@
assert(expr_end >= expr_start);
assert(*(expr_start-1) == '{');
- assert(*expr_end == '}' || *expr_end == '!' || *expr_end == ':');
+ assert(*expr_end == '}' || *expr_end == '!' || *expr_end == ':' ||
+ *expr_end == '=');
/* If the substring is all whitespace, it's an error. We need to catch this
here, and not when we call PyParser_SimpleParseStringFlagsFilename,
@@ -4997,9 +4998,9 @@
struct compiling *c, const node *n);
/* Parse the f-string at *str, ending at end. We know *str starts an
- expression (so it must be a '{'). Returns the FormattedValue node,
- which includes the expression, conversion character, and
- format_spec expression.
+ expression (so it must be a '{'). Returns the FormattedValue node, which
+ includes the expression, conversion character, format_spec expression, and
+ optionally the text of the expression (if = is used).
Note that I don't do a perfect job here: I don't make sure that a
closing brace doesn't match an opening paren, for example. It
@@ -5016,7 +5017,12 @@
const char *expr_end;
expr_ty simple_expression;
expr_ty format_spec = NULL; /* Optional format specifier. */
- int conversion = -1; /* The conversion char. -1 if not specified. */
+ int conversion = -1; /* The conversion char. Use default if not
+ specified, or !r if using = and no format
+ spec. */
+ int equal_flag = 0; /* Are we using the = feature? */
+ PyObject *expr_text = NULL; /* The text of the expression, used for =. */
+ const char *expr_text_end;
/* 0 if we're not in a string, else the quote char we're trying to
match (single or double quote). */
@@ -5033,7 +5039,7 @@
/* Can only nest one level deep. */
if (recurse_lvl >= 2) {
ast_error(c, n, "f-string: expressions nested too deeply");
- return -1;
+ goto error;
}
/* The first char must be a left brace, or we wouldn't have gotten
@@ -5061,7 +5067,7 @@
ast_error(c, n,
"f-string expression part "
"cannot include a backslash");
- return -1;
+ goto error;
}
if (quote_char) {
/* We're inside a string. See if we're at the end. */
@@ -5106,7 +5112,7 @@
} else if (ch == '[' || ch == '{' || ch == '(') {
if (nested_depth >= MAXLEVEL) {
ast_error(c, n, "f-string: too many nested parenthesis");
- return -1;
+ goto error;
}
parenstack[nested_depth] = ch;
nested_depth++;
@@ -5114,22 +5120,38 @@
/* Error: can't include a comment character, inside parens
or not. */
ast_error(c, n, "f-string expression part cannot include '#'");
- return -1;
+ goto error;
} else if (nested_depth == 0 &&
- (ch == '!' || ch == ':' || ch == '}')) {
- /* First, test for the special case of "!=". Since '=' is
- not an allowed conversion character, nothing is lost in
- this test. */
- if (ch == '!' && *str+1 < end && *(*str+1) == '=') {
- /* This isn't a conversion character, just continue. */
- continue;
+ (ch == '!' || ch == ':' || ch == '}' ||
+ ch == '=' || ch == '>' || ch == '<')) {
+ /* See if there's a next character. */
+ if (*str+1 < end) {
+ char next = *(*str+1);
+
+ /* For "!=". since '=' is not an allowed conversion character,
+ nothing is lost in this test. */
+ if ((ch == '!' && next == '=') || /* != */
+ (ch == '=' && next == '=') || /* == */
+ (ch == '<' && next == '=') || /* <= */
+ (ch == '>' && next == '=') /* >= */
+ ) {
+ *str += 1;
+ continue;
+ }
+ /* Don't get out of the loop for these, if they're single
+ chars (not part of 2-char tokens). If by themselves, they
+ don't end an expression (unlike say '!'). */
+ if (ch == '>' || ch == '<') {
+ continue;
+ }
}
+
/* Normal way out of this loop. */
break;
} else if (ch == ']' || ch == '}' || ch == ')') {
if (!nested_depth) {
ast_error(c, n, "f-string: unmatched '%c'", ch);
- return -1;
+ goto error;
}
nested_depth--;
int opening = parenstack[nested_depth];
@@ -5141,7 +5163,7 @@
"f-string: closing parenthesis '%c' "
"does not match opening parenthesis '%c'",
ch, opening);
- return -1;
+ goto error;
}
} else {
/* Just consume this char and loop around. */
@@ -5154,12 +5176,12 @@
let's just do that.*/
if (quote_char) {
ast_error(c, n, "f-string: unterminated string");
- return -1;
+ goto error;
}
if (nested_depth) {
int opening = parenstack[nested_depth - 1];
ast_error(c, n, "f-string: unmatched '%c'", opening);
- return -1;
+ goto error;
}
if (*str >= end)
@@ -5170,7 +5192,22 @@
conversion or format_spec. */
simple_expression = fstring_compile_expr(expr_start, expr_end, c, n);
if (!simple_expression)
- return -1;
+ goto error;
+
+ /* Check for =, which puts the text value of the expression in
+ expr_text. */
+ if (**str == '=') {
+ *str += 1;
+ equal_flag = 1;
+
+ /* Skip over ASCII whitespace. No need to test for end of string
+ here, since we know there's at least a trailing quote somewhere
+ ahead. */
+ while (Py_ISSPACE(**str)) {
+ *str += 1;
+ }
+ expr_text_end = *str;
+ }
/* Check for a conversion char, if present. */
if (**str == '!') {
@@ -5182,13 +5219,19 @@
*str += 1;
/* Validate the conversion. */
- if (!(conversion == 's' || conversion == 'r'
- || conversion == 'a')) {
+ if (!(conversion == 's' || conversion == 'r' || conversion == 'a')) {
ast_error(c, n,
"f-string: invalid conversion character: "
"expected 's', 'r', or 'a'");
- return -1;
+ goto error;
}
+
+ }
+ if (equal_flag) {
+ Py_ssize_t len = expr_text_end-expr_start;
+ expr_text = PyUnicode_FromStringAndSize(expr_start, len);
+ if (!expr_text)
+ goto error;
}
/* Check for the format spec, if present. */
@@ -5202,7 +5245,7 @@
/* Parse the format spec. */
format_spec = fstring_parse(str, end, raw, recurse_lvl+1, c, n);
if (!format_spec)
- return -1;
+ goto error;
}
if (*str >= end || **str != '}')
@@ -5213,20 +5256,31 @@
assert(**str == '}');
*str += 1;
+ /* If we're in = mode, and have no format spec and no explict conversion,
+ set the conversion to 'r'. */
+ if (equal_flag && format_spec == NULL && conversion == -1) {
+ conversion = 'r';
+ }
+
/* And now create the FormattedValue node that represents this
entire expression with the conversion and format spec. */
*expression = FormattedValue(simple_expression, conversion,
- format_spec, LINENO(n), n->n_col_offset,
- n->n_end_lineno, n->n_end_col_offset,
- c->c_arena);
+ format_spec, expr_text, LINENO(n),
+ n->n_col_offset, n->n_end_lineno,
+ n->n_end_col_offset, c->c_arena);
if (!*expression)
- return -1;
+ goto error;
return 0;
unexpected_end_of_string:
ast_error(c, n, "f-string: expecting '}'");
+ /* Falls through to error. */
+
+error:
+ Py_XDECREF(expr_text);
return -1;
+
}
/* Return -1 on error.