gh-74185: repr() of ImportError now contains attributes name and path #136770

Yoav11 · 2025-07-19T08:07:56Z

This PR was created during Europython 2025's spring weekend.

This is a patch on #1011. authored by serhiy-storchaka and arhadthedev

Issue: repr() of ImportError misses keyword arguments name and path #74185

python-cla-bot · 2025-07-19T08:08:00Z

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bedevere-app · 2025-07-19T08:26:34Z

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StanFromIreland · 2025-07-19T08:28:42Z

You need to sign the CLA.

Requesting @encukou who wanted to finish this per #1011 (comment)

Objects/exceptions.c

picnixz · 2025-07-19T10:11:51Z

Objects/exceptions.c

+
+    if (r && (exc->name || exc->path)) {
+        /* remove ')' */
+        Py_SETREF(r, PyUnicode_Substring(r, 0, PyUnicode_GET_LENGTH(r) - 1));


Let's use PyUnicodeWriter instead to avoids re-creating strings:

PyUnicodeWriter *writer = PyUnicodeWriter_Create(0); if (writer == NULL) goto error; if (PyUnicodeWriter_WriteSubstring(writer, r, 0, l - 1) < 0) goto error; if (exc->name) { if (hasargs) { if (PyUnicodeWriter_WriteASCII(writer, ", ", 2) < 0) goto error; } ... } ... return PyUnicodeWriter_Finish(writer); error: /* cleanup */

Objects/exceptions.c

picnixz · 2025-07-19T11:03:34Z

Objects/exceptions.c

+    PyObject *r = BaseException_repr(self);
+    PyImportErrorObject *exc = PyImportErrorObject_CAST(self);
+    PyUnicodeWriter *writer = PyUnicodeWriter_Create(0);
+    if (writer == NULL) goto error;


Sorry but my suggestion wasn't PEP-7 compliant. So you should rewrite this function in a PEP-7 compliant way.

@picnixz are you referring to braces are required everywhere, even where C permits them to be omitted ?

picnixz · 2025-07-19T11:04:34Z

Objects/exceptions.c

+        if (PyUnicodeWriter_WriteASCII(writer, "name='", 6) < 0) goto error;
+        if (PyUnicodeWriter_WriteSubstring(writer, exc->name, 0, PyUnicode_GET_LENGTH(exc->name)) < 0) goto error;
+        if (PyUnicodeWriter_WriteASCII(writer, "'", 1) < 0) goto error;


For this one, as you're using the entire "exc->name", you can just use PyUnicodeWriter_Format("name=%R", exc->name") instead.

picnixz · 2025-07-19T11:05:12Z

Objects/exceptions.c

+    error:
+        Py_XDECREF(r);
+        PyUnicodeWriter_Discard(writer);
+        return NULL;


Suggested change

error:

Py_XDECREF(r);

PyUnicodeWriter_Discard(writer);

return NULL;

error:

Py_XDECREF(r);

PyUnicodeWriter_Discard(writer);

return NULL;

picnixz · 2025-07-19T11:07:23Z

Lib/test/test_exceptions.py

+        try:
+            import does_not_exist  # type: ignore[import] # noqa: F401
+        except ModuleNotFoundError as e:


You can use with self.assertRaises(ImportError) as cm and check cm.exception attributes.

picnixz · 2025-07-19T11:12:17Z

Objects/exceptions.c

@@ -1864,6 +1864,41 @@ ImportError_reduce(PyObject *self, PyObject *Py_UNUSED(ignored))
    return res;
 }

+static PyObject *
+ImportError_repr(PyObject *self)


Are there other exceptions that will benefit from having keywords in their reprs? AFAICT, the keywords are only rendered if they were passed to the constructor as keyword arguments. In particular, we could make a generic repr helper for that which takes into account them, something like:

static PyObject * repr_with_keywords(PyObject *exc, const char * const *kwlist) { /* format using kwlist[i]=getattr(exc, kwlist[i]) * with kwlist NULL-terminated */ }

Its usage would be

static char *kwlist[] = {"name", "path", NULL}; repr_with_keywords(exc, kwlist)

For now, let's hold off this idea as I don't know if it can be useful. But this can be worth investigating instead of storing the given keywords explicitly.

yes - AFAIK only ImportError and ModuleNotFoundError (which hinnerits this functionality as per the tests) have optional arguments ? but makes sense to me that if other exception types in the future have optionals then we could extract this out.

Yes, but let's do it in a follow-up PR so that we can revert the helper commit more easily. Also it depends on whether we would store the keywords passed to the constructor (this is #11580)

ynir3 · 2025-07-19T12:29:56Z

@picnixz any more comments ? :)

picnixz · 2025-07-19T12:41:33Z

Objects/exceptions.c

+            goto error;
+        }
+    }
+    if (PyUnicodeWriter_WriteASCII(writer, ")", 1) < 0) goto error;


picnixz · 2025-07-19T12:41:56Z

Objects/exceptions.c

+    if (writer == NULL) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteSubstring(writer, r, 0, PyUnicode_GET_LENGTH(r)-1) < 0) {


Plese wrap lines under 80 chars.

picnixz · 2025-07-19T12:42:53Z

Objects/exceptions.c

+ImportError_repr(PyObject *self)
+{
+    int hasargs = PyTuple_GET_SIZE(((PyBaseExceptionObject *)self)->args) != 0;
+    PyObject *r = BaseException_repr(self);


This needs to be decrefed after it's been used. By doing so, you can also remove the Py_XDECREF(r) call at the end as it won't be needed anymore. I also suggest calling this function only after the writer has been successfully created.

yup makes sense, thanks!

serhiy-storchaka and others added 5 commits July 19, 2025 09:43

bpo-29999: repr() of ImportError now contains attributes name and path.

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bedevere-app bot mentioned this pull request Jul 19, 2025

repr() of ImportError misses keyword arguments name and path #74185

Open

Yoav11 changed the title ~~gh-74185: (patch) repr() of ImportError now contains attributes name and path.~~ gh-74185: repr() of ImportError now contains attributes name and path. (patch) Jul 19, 2025

ynir3 added 2 commits July 19, 2025 10:23

add test_ModuleNotFoundError_repr_with_failed_import

126be20

add test_ModuleNotFoundError_repr_with_failed_import

4a97f5c

StanFromIreland requested review from encukou and serhiy-storchaka July 19, 2025 08:28

ynir3 added 6 commits July 19, 2025 10:36

add blurb

852da8c

add noqa:F401

6ab7362

remove whitespace

12c2293

fix trailing-whitespace

a53da37

use ComplexExtendsException

5b6d626

return to non-macro style

951e0a1

picnixz reviewed Jul 19, 2025

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Objects/exceptions.c Outdated Show resolved Hide resolved

use modern field initializers

8fbfd18

picnixz reviewed Jul 19, 2025

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Objects/exceptions.c Outdated Show resolved Hide resolved

remove un-necessary casts

458bcd0

picnixz changed the title ~~gh-74185: repr() of ImportError now contains attributes name and path. (patch)~~ gh-74185: repr() of ImportError now contains attributes name and path Jul 19, 2025

ynir3 added 3 commits July 19, 2025 12:52

use PyUnicodeWriter

fa2f884

fix trailing whitespace

35a6a29

reduce nesting

6e416c6

picnixz reviewed Jul 19, 2025

View reviewed changes

ynir3 added 2 commits July 19, 2025 13:14

use PyUnicdodeWriter_Format and if statement braces

aa75f6a

indentation

8b5e4ed

picnixz reviewed Jul 19, 2025

View reviewed changes

move decref

28545e5

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Yoav11 commented Jul 19, 2025 •

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