GeezerVison

Example of code to copy a frozendict or a dict (from Objects/typeobject.c):

    PyObject *dict;
    if (PyFrozenDict_Check(ctx->orig_dict)) {
        dict = PyFrozenDict_AsDict(ctx->orig_dict);
    }
    else {
        dict = PyDict_Copy(ctx->orig_dict);
    }
    if (dict == NULL) {
        goto error;
    }

What's the motivation for this change?

Would something like PyAnyDict_AsNewDict be more useful?

C API WG is fine with the naming?

That's for a vote; I can't speak for the entire WG.
FWIW, PEP 814 wasn't consulted with the C API WG in the first place. Personally I didn't follow it very closely. Things like making PyDict_Copy accept frozendict (which is being reverted here) aren't specified in the PEP anyway.

This PR was big, so I merged unrelated changes as separated changes:

• commit 2cd0ddf fix frozendict.items() ^ frozendict.items().
• commit 0c29f83 modify PyDict_Copy() to no longer accept frozendict

@ZeroIntensity convinced me that supporting frozendict in PyDict_Copy() is a bad idea.

What's the motivation for this change?

When a function using PyDict_Copy() is modified to support frozendict, I have to write code like that:

    PyObject *dict;
    if (PyFrozenDict_Check(orig_dict)) {
        dict = PyDict_New();
        if (dict == NULL) {
            goto error;
        }
        if (PyDict_Merge(dict, orig_dict, 1) < 0) {
            Py_DECREF(dict);
            goto error;
        }
    }
    else {
        dict = PyDict_Copy(orig_dict);
        if (dict == NULL) {
            goto error;
        }
    }

I have to copy/paste this code. I would prefer to have a function doing that: convert a frozendict to a dict, copy a dict, or fail if the argument is not a dict or a frozendict. A dedicated function may be more efficient than PyDict_New()+PyDict_Merge().

Would something like PyAnyDict_AsNewDict be more useful?

Oh, I prefer this function over PyFrozenDict_AsDict().

@ZeroIntensity: What do you think of adding a new PyAnyDict_AsNewDict() function?

I think this will be useful. When 3.15 comes out, there will be plenty of APIs that assume an input dictionary is mutable, and thus can't be used with frozendict. Being able to get a dictionary out of a frozendict will help adoption in that sense.

Is there an east way to convert a dictionary into a frozendict? Another potential use-case would be if you're trying to implement a function like this in C:

def adjust_frozendict(data: frozendict) -> frozendict:
    mutable = dict(data)
    mutable["whatever"] = 123
    return frozendict(mutable)

Ok, I renamed the function to PyAnyDict_AsNewDict(). It accepts dict and frozendict and creates a new dict.

Is there an easy way to convert a dictionary into a frozendict?

Yes, call PyFrozenDict_New(dict): https://docs.python.org/dev/c-api/dict.html#c.PyFrozenDict_New

Currently, dict = PyObject_CallOneArg((PyObject*)&PyDict_Type, frozendict) can be used to convert a frozendict to a dict. The code is harder to read and harder to "discover", but it just works.

This PR is stale because it has been open for 30 days with no activity.

I lost track of this function and Python 3.15 beta1 has been released without it. We are now past the feature freeze, so I don't think that it's worth it to add such function.

We can revisit this function later if there is a need for it. I close th PR.