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Sep 24, 2021
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bpo-20524: adds better error message for .format() #28310

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da09019
bpo-20524: adds better error message for `.format()`
sobolevn Sep 13, 2021
a4db2fd
Addresses review
sobolevn Sep 13, 2021
602f200
Adds an extra test for unicode in error message
sobolevn Sep 13, 2021
022fd1a
Addresses review
sobolevn Sep 24, 2021
4a11a03
Update test_format.py
sobolevn Sep 24, 2021
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28 changes: 28 additions & 0 deletions Lib/test/test_format.py
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Original file line number Diff line number Diff line change
Expand Up @@ -519,5 +519,33 @@ def test_with_an_underscore_and_a_comma_in_format_specifier(self):
with self.assertRaisesRegex(ValueError, error_msg):
'{:_,}'.format(1)

def test_better_error_message_format(self):
# https://bugs.python.org/issue20524
for value in [12j, 12, 12.0, "12"]:
with self.subTest(value=value):
# The format spec must be invalid for all types we're testing.
# '%M' will suffice.
bad_format_spec = '%M'
err = re.escape("Invalid format specifier "
f"'{bad_format_spec}' for object of type "
f"'{type(value).__name__}'")
with self.assertRaisesRegex(ValueError, err):
f"xx{{value:{bad_format_spec}}}yy".format(value=value)

# Also test the builtin format() function.
with self.assertRaisesRegex(ValueError, err):
format(value, bad_format_spec)

# Also test f-strings.
with self.assertRaisesRegex(ValueError, err):
eval("f'xx{value:{bad_format_spec}}yy'")

def test_unicode_in_error_message(self):
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I hadn't noticed this test before. It's great, especially because of the work in using "kind" to compute the actual error message.

str_err = re.escape(
"Invalid format specifier '%ЫйЯЧ' for object of type 'str'")
with self.assertRaisesRegex(ValueError, str_err):
"{a:%ЫйЯЧ}".format(a='a')


if __name__ == "__main__":
unittest.main()
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2021-09-13-14-59-01.bpo-20524.PMQ1Fh.rst
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@@ -0,0 +1,3 @@
Improves error messages on ``.format()`` operation for ``str``, ``float``,
``int``, and ``complex``. New format now shows the problematic pattern and
the object type.
26 changes: 19 additions & 7 deletions Python/formatter_unicode.c
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Original file line number Diff line number Diff line change
Expand Up @@ -162,7 +162,8 @@ DEBUG_PRINT_FORMAT_SPEC(InternalFormatSpec *format)
if failure, sets the exception
*/
static int
parse_internal_render_format_spec(PyObject *format_spec,
parse_internal_render_format_spec(PyObject *obj,
PyObject *format_spec,
Py_ssize_t start, Py_ssize_t end,
InternalFormatSpec *format,
char default_type,
Expand Down Expand Up @@ -279,8 +280,19 @@ parse_internal_render_format_spec(PyObject *format_spec,
/* Finally, parse the type field. */

if (end-pos > 1) {
/* More than one char remain, invalid format specifier. */
PyErr_Format(PyExc_ValueError, "Invalid format specifier");
/* More than one char remains, so this is an invalid format
specifier. */
/* Create a temporary object that contains the format spec we're
operating on. It's format_spec[start:end] (in Python syntax). */
PyObject* actual_format_spec = PyUnicode_FromKindAndData(kind,
(char*)data + kind*start,
end-start);
if (actual_format_spec != NULL) {
PyErr_Format(PyExc_ValueError,
"Invalid format specifier '%U' for object of type '%.200s'",
actual_format_spec, Py_TYPE(obj)->tp_name);
Py_DECREF(actual_format_spec);
}
return 0;
}

Expand Down Expand Up @@ -1444,7 +1456,7 @@ _PyUnicode_FormatAdvancedWriter(_PyUnicodeWriter *writer,
}

/* parse the format_spec */
if (!parse_internal_render_format_spec(format_spec, start, end,
if (!parse_internal_render_format_spec(obj, format_spec, start, end,
&format, 's', '<'))
return -1;

Expand Down Expand Up @@ -1480,7 +1492,7 @@ _PyLong_FormatAdvancedWriter(_PyUnicodeWriter *writer,
}

/* parse the format_spec */
if (!parse_internal_render_format_spec(format_spec, start, end,
if (!parse_internal_render_format_spec(obj, format_spec, start, end,
&format, 'd', '>'))
goto done;

Expand Down Expand Up @@ -1536,7 +1548,7 @@ _PyFloat_FormatAdvancedWriter(_PyUnicodeWriter *writer,
return format_obj(obj, writer);

/* parse the format_spec */
if (!parse_internal_render_format_spec(format_spec, start, end,
if (!parse_internal_render_format_spec(obj, format_spec, start, end,
&format, '\0', '>'))
return -1;

Expand Down Expand Up @@ -1575,7 +1587,7 @@ _PyComplex_FormatAdvancedWriter(_PyUnicodeWriter *writer,
return format_obj(obj, writer);

/* parse the format_spec */
if (!parse_internal_render_format_spec(format_spec, start, end,
if (!parse_internal_render_format_spec(obj, format_spec, start, end,
&format, '\0', '>'))
return -1;

Expand Down