The globals argument to eval() should accept frozendict

[rhettinger]

>>> eval('word', globals=frozendict({'word': 'hello'}))
Traceback (most recent call last):
  File "<pyshell#19>", line 1, in <module>
    eval('word', globals=frozendict({'word': 'hello'}))
TypeError: globals must be a real dict; try eval(expr, {}, mapping)

Linked PRs

• gh-145055: Accept frozendict for globals in exec() and eval() #145072

[rhettinger]

Also json.dumps needs to be frozendict aware.

json.dumps(frozendict({'word': 'hello'}))
Traceback (most recent call last):
  File "<pyshell#23>", line 1, in <module>
    json.dumps(frozendict({'word': 'hello'}))
  File "/Users/raymond/cpython/Lib/json/__init__.py", line 234, in dumps
    return _default_encoder.encode(obj)
  File "/Users/raymond/cpython/Lib/json/encoder.py", line 202, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/Users/raymond/cpython/Lib/json/encoder.py", line 263, in iterencode
    return _iterencode(o, 0)
  File "/Users/raymond/cpython/Lib/json/encoder.py", line 182, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type frozendict is not JSON serializable

[skirpichev]

$ git grep PyDict_Check Python/ Objects/ Modules/|wc -l
300

I guess, that a lot of cases could support frozendict's as well. Just a random one:

$ git grep PyDict_Check Modules/_decimal
Modules/_decimal/_decimal.c:    if (!PyDict_Check(val)) {
Modules/_decimal/_decimal.c:        else if (PyDict_Check(w)) {
Modules/_decimal/_decimal.c:        if (!PyDict_Check(override)) {
$ ./python -q
>>> import decimal as _cdecimal
>>> import _pydecimal
>>> ctx_c = _cdecimal.getcontext()
>>> ctx_py = _pydecimal.getcontext()
>>> ctx_py.traps == frozendict()
False
>>> ctx_c.traps == frozendict()
Traceback (most recent call last):
  File "<python-input-12>", line 1, in <module>
    ctx_c.traps == frozendict()
ValueError: invalid signal dict

[skirpichev]

For globals I'm not sure. Documentation says:

If the globals dictionary is present and does not contain a value for the key __builtins__, a reference to the dictionary of the built-in module builtins is inserted under that key before source is parsed.

It's not hard to relax constraint on the globals type (see patch below), but this may lead to less useful error messages:

>>> d = frozendict({'word': 'hello', '__builtins__': globals()['__builtins__']})
>>> eval('word', globals=d)
'hello'
>>> eval('word', globals=frozendict({'word': 'hello'}))
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    eval('word', globals=frozendict({'word': 'hello'}))
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'frozendict' object does not support item assignment

So, if frozendict does make sense here - any Mapping too.

Details

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index af3fcca7455..39f8e0943b8 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -2661,7 +2661,7 @@ _PyDict_LoadGlobalStackRef(PyDictObject *globals, PyDictObject *builtins, PyObje
 PyObject *
 _PyDict_LoadBuiltinsFromGlobals(PyObject *globals)
 {
-    if (!PyDict_Check(globals)) {
+    if (!PyAnyDict_Check(globals)) {
         PyErr_BadInternalCall();
         return NULL;
     }
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 493a6e0413d..269108be21c 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -1034,7 +1034,7 @@ builtin_eval_impl(PyObject *module, PyObject *source, PyObject *globals,
         PyErr_SetString(PyExc_TypeError, "locals must be a mapping");
         return NULL;
     }
-    if (globals != Py_None && !PyDict_Check(globals)) {
+    if (globals != Py_None && !PyAnyDict_Check(globals)) {
         PyErr_SetString(PyExc_TypeError, PyMapping_Check(globals) ?
             "globals must be a real dict; try eval(expr, {}, mapping)"
             : "globals must be a dict");
diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index ec8c2d12ab2..3b2c0136fba 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -1347,7 +1347,7 @@ static PyObject *
 run_eval_code_obj(PyThreadState *tstate, PyCodeObject *co, PyObject *globals, PyObject *locals)
 {
     /* Set globals['__builtins__'] if it doesn't exist */
-    if (!globals || !PyDict_Check(globals)) {
+    if (!globals || !PyAnyDict_Check(globals)) {
         PyErr_SetString(PyExc_SystemError, "globals must be a real dict");
         return NULL;
     }

[hugovk]

Also json.dumps needs to be frozendict aware.

See PR #144903 and the umbrella issue #141510.

[vstinner]

I wrote #145072 to accept frozendict for globals in exec() and eval().

It's not hard to relax constraint on the globals type (see patch below), but this may lead to less useful error messages:
TypeError: 'frozendict' object does not support item assignment

Maybe exec() and eval() documentation should properly document this case?

[picnixz]

For exec() and dict/exact dict/mapping for exec(), there were some past discussions: See #76796 and #131811 (and #131811 (comment)) so those issues could also be closed/moved forward once this one is addressed I guess.

[vstinner]

skirpichev self-assigned this

Oh, I didn't notice that @skirpichev assigned the issue to himself. Sorry, I created a PR since I already had a full implementation locally. I planned to publish it once other frozendict changes landed.

[skirpichev]

I created a PR since I already had a full implementation locally.

Please go ahead. I have doubts about initial proposal, IMO frozendict support here will only complicate docs.