[C API] Add PyDict_ContainsString() function

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Feature or enhancement

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Proposal:

Most, if not all, PyDict C APIs have a "String" flavor where the key argument is expressed as a UTF-8 encoded bytes string. But the PyDict_Contains() API is missing such variant.

I suppose that it was not proposed before since PyDict_GetItemString(dict, key) != NULL can already be used. My problem is that PyDict_GetItemString() ignores errors: I would like to report errors.

The newly added PyDict_GetItemStringRef() can be used to check if a dictionary has a key and report errors, but it requires calling Py_DECREF() which is not convenient. Example:

PyObject *value;
if (PyDict_GetItemStringRef(dict, key, &value) < 0) {
    // ... handle error ...
}
int has_value = (value != NULL);
Py_XDECREF(value);
// ... use has_value ...

I would like to be able to replace this code with:

int has_value = PyDict_ContainsString(dict, key);
if (has_value < 0) {    
    // ... handle error ...
}
// ... use has_value ...

There is no need to INCREF/DECREF just to check if a dictionary has a key.

Linked PRs

• gh-108314: Add PyDict_ContainsString() function #108323
• [3.12] gh-108314: PyDict_GetItemString() mentions UTF-8 #108448
• [3.11] [3.12] gh-108314: PyDict_GetItemString() mentions UTF-8 (GH-108448) #108489

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There is already an abstract PyMapping_HasKeyString() function. Sadly, on error, this function clears the exception and returns 0 :-(

[corona10]

Has this already been discussed elsewhere?

FYI, there was the discussion with adding this API.
capi-workgroup/problems#23

[encukou]

And here: #100100

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I added the function to pythoncapi-compat: python/pythoncapi-compat@4734c8e