8000 gh-106672: C API: Report indiscriminately ignored errors by serhiy-storchaka · Pull Request #106674 · python/cpython · GitHub
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gh-106672: C API: Report indiscriminately ignored errors #106674

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Merged
merged 18 commits into from
Nov 7, 2023
Merged

gh-106672: C API: Report indiscriminately ignored errors #106674

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e134bad
gh-106672: C API: Report indiscriminately ignored errors
serhiy-storchaka Jul 12, 2023
00ce038
Update output messsages.
serhiy-storchaka Jul 12, 2023
168f92a
Add an entry in What's New.
serhiy-storchaka Jul 12, 2023
884da66
Merge branch 'main' into capi-write-unraisable-for-ignored-errors
serhiy-storchaka Jul 12, 2023
58dbac5
Merge branch 'main' into capi-write-unraisable-for-ignored-errors
serhiy-storchaka Aug 7, 2023
07c8250
Fix smelly symbol.
serhiy-storchaka Aug 7, 2023
56e3a49
Remove PyDict_GetItem(dict, invalid_key) from test_dict_capi().
serhiy-storchaka Aug 7, 2023
4e13132
Merge branch 'main' into capi-write-unraisable-for-ignored-errors
serhiy-storchaka Aug 7, 2023
b5a661b
Fix regressions in handling NULLs.
serhiy-storchaka Aug 7, 2023
ab5eb8f
Merge branch 'main' into capi-write-unraisable-for-ignored-errors
serhiy-storchaka Aug 12, 2023
c681ce2
Merge branch 'main' into capi-write-unraisable-for-ignored-errors
serhiy-storchaka Aug 26, 2023
82efd1c
Fix merging error.
serhiy-storchaka Aug 26, 2023
c687ff8
Merge branch 'main' into capi-write-unraisable-for-ignored-errors
serhiy-storchaka Nov 5, 2023
310ae51
Add more suggestions.
serhiy-storchaka Nov 5, 2023
241576a
Improve error messages for ignoring errors set before the calls.
serhiy-storchaka Nov 5, 2023
fd50ea9
Apply suggestions from code review
serhiy-storchaka Nov 6, 2023
587b3cc
Address review comments.
serhiy-storchaka Nov 6, 2023
bfb206a
Remove non-existing cases.
serhiy-storchaka Nov 6, 2023
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Address review comments.
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@serhiy-storchaka
serhiy-storchaka committed Nov 6, 2023
commit 587b3ccd842317e3d097eb7ce63953b29b94fcb8
12 changes: 6 additions & 6 deletions Objects/abstract.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2470,7 +2470,7 @@ PyMapping_HasKeyWithError(PyObject *obj, PyObject *key)
int
PyMapping_HasKeyString(PyObject *obj, const char *key)
{
PyObject *dummy;
PyObject *value;
int rc;
if (obj == NULL) {
// For backward compatibility.
Expand All @@ -2479,7 +2479,7 @@ PyMapping_HasKeyString(PyObject *obj, const char *key)
rc = -1;
}
else {
rc = PyMapping_GetOptionalItemString(obj, key, &dummy);
rc = PyMapping_GetOptionalItemString(obj, key, &value);
}
if (rc < 0) {
PyErr_FormatUnraisable(
Expand All @@ -2497,14 +2497,14 @@ PyMapping_HasKeyString(PyObject *obj, const char *key)
"PyMapping_GetOptionalItemString() or PyMapping_GetItemString()");
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@vstinner vstinner Nov 6, 2023 •
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Can these 3 functions be called with an exception set? They don't override the exception? That sounds surprising. I would prefer suggesting to not call the function with an exception set. What do you think?

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Got catch. Indeed, PyMapping_GetOptionalItemString() can only return 0 if no exception is set, so this condition is always false. Also, the alternative functions also can clear exceptions.

I think that we should classify the C API by classes:

  1. Function that can be called when an exception is set, and they do not change it.
  2. Function that can be called when an exception is set, and they do not change it unless they fail.
  3. Function that can be called when an exception is set, but they can change it even at success.
  4. Function that can be called when an exception is set, but the result is ambiguous in some cases (you cannot distinguish some successful results from failure).
  5. Function that should never be called when an exception is set.

There may be more classes.

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In the general case, to write safe code handling a raised exception, I think the safest option is to keep the exception aside using PyErr_GetRaisedException(). Maybe today some functions are perfectly fine and never override the currently raised exception. But what if tomorrow their implementation changes, and they may start to clear the currently raised exception?

In Python, in an except: block, there is no "currently raised exception" in the C level, even if sys.exc_info() returns the exception. The difference between PyThreadState.exc_info and PyThreadState.current_exception is subtle.

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This is why it should be clearly documented.

Obviously you can call PyErr_Occurred(), PyErr_GetRaisedException() or PyErr_WriteUnraisable() when an exception is set.

return 0;
}
Py_XDECREF(dummy);
Py_XDECREF(value);
return rc;
}

int
PyMapping_HasKey(PyObject *obj, PyObject *key)
{
PyObject *dummy;
PyObject *value;
int rc;
if (obj == NULL || key == NULL) {
// For backward compatibility.
Expand All @@ -2513,7 +2513,7 @@ PyMapping_HasKey(PyObject *obj, PyObject *key)
rc = -1;
}
else {
rc = PyMapping_GetOptionalItem(obj, key, &dummy);
rc = PyMapping_GetOptionalItem(obj, key, &value);
}
if (rc < 0) {
PyErr_FormatUnraisable(
Expand All @@ -2531,7 +2531,7 @@ PyMapping_HasKey(PyObject *obj, PyObject *key)
"PyMapping_GetOptionalItem() or PyObject_GetItem()");
return 0;
}
Py_XDECREF(dummy);
Py_XDECREF(value);
return rc;
}

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