[issue34595] PyUnicode_FromFormat(): add %T format for an object type name

[STINNER Victor]

STINNER Victor <vstinner at redhat.com> added the comment:

> In some cases we have the type itself, not an instance. So it makes sense to make %T an equivalent of arg->tp_name instead of Py_TYPE(arg)->tp_name.

"arg->tp_name" is rare in the code base, whereas "Py_TYPE(arg)->tp_name" is a very common pattern.

I'm not sure that a formatter is needed for "arg->tp_name", you can already use "%s" with "arg->tp_name", no?

My intent was to make the C code less verbose, respect the PEP 399, but also indirectly avoid the implicit borrowed reference of Py_TYPE() :-)
https://pythoncapi.readthedocs.io/bad_api.html#borrowed-references


> On Python side, you need to output either short name obj.__class__.__name__ or full qualified name obj.__class__.__module__ + '.' + obj.__class__.__qualname__ with exception that the module name should be omitted if it is 'builtins'.

Sometimes, the qualified name would be more appropriate, but it's sometimes tricky to decide if the short name, qualified name or fully qualified name is the "right" name... So I chose to restrict this issue to the most common case, Py_TYPE(arg)->tp_name :-)

Ah, and changing strings is a risk of breaking the backward compatibility. For example, cause issue with pickle. So it should be discussed on a case by case basis.

Moreover, if you want to change a string, the Python code should be updated as well. I suggest to open a new issue to discuss that.

Don't get me wrong, I'm interested to do these changes, but it's a wider project :-)


> obj.__class__.__qualname__ if obj.__class__.__module__ == 'builtins' else f'{obj.__class__.__module__}.{obj.__class__.__qualname__}'
>
> The case of the module name '__main__' can be handled specially too.
> Obviously it is desirable to have a more handy way of writing such expression.

To be honest, I also considered to proposed a second formatter to do something like that :-) But as you explained, I'm not sure which name is the good name: qualified or fully qualified (with module name)?

First of all, would it help to have a *function* to get these names? Maybe we could first use such functions before discussing adding a new formatter in PyUnicode_FromFormat()?

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<https://bugs.python.org/issue34595>
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