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gh-130821: Add type information to wrong type error messages #130835

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donBarbos
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@donBarbos donBarbos commented Mar 4, 2025

I got next output for use case from issue:

Foo.__int__() must return an int, not NoneType
Foo.__float__() must return a float, not NoneType
Foo.__bytes__() must return a bytes, not NoneType
Foo.__complex__() must return a complex, not NoneType
Foo.__bool__() must return a bool, not NoneType
Foo.__str__() must return a str, not NoneType

but we still have a lot of other places where wrong type errors have inconsistent messages. should they be updated too?

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@jstasiak jstasiak left a comment

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Drive-by comment: does it make sense to have tests for these changes?

@donBarbos
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Drive-by comment: does it make sense to have tests for these changes?

it seems that we don't check the text of error messages if we don't want to check the error type itself

@skirpichev skirpichev self-requested a review April 28, 2025 13:19
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@JelleZijlstra JelleZijlstra left a comment

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I think many of the changes in wording are not clear improvements.

@@ -1421,17 +1423,17 @@ _PyNumber_Index(PyObject *item)

if (!PyLong_Check(result)) {
PyErr_Format(PyExc_TypeError,
"__index__ returned non-int (type %.200s)",
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I don't see much reason to change this error message either.

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@donBarbos donBarbos Apr 29, 2025

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I changed it to the more common way as you recommended elsewhere: __method__() must return an int, not ...
and added type info before method name, like for other methods

@@ -2435,10 +2436,8 @@ method_output_as_list(PyObject *o, PyObject *meth)
PyThreadState *tstate = _PyThreadState_GET();
if (_PyErr_ExceptionMatches(tstate, PyExc_TypeError)) {
_PyErr_Format(tstate, PyExc_TypeError,
"%.200s.%U() returned a non-iterable (type %.200s)",
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Here I strongly prefer the old message. Iterable is not a type, it's a category of types.

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what do you think about new message: "%T.%U() must return an iterable, not %T"

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4 participants