[Bug]: Serialization with dictionaries where keys are tuple fails

[Andrew-S-Rosen]

Email (Optional)

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Version

2024.2.26

Which OS(es) are you using?

• MacOS
• Windows
• Linux

What happened?

When trying to JSON serialize (e.g. dumpfn) a dictionary where the keys are of type tuple, an error is raised. This makes sense, because the Python JSON encoder doesn't support this, but perhaps it is worthwhile to consider supporting it in some way through monty.

Potentially related:

• Cannot override JSON encoding of basic type subclasses python/cpython#56866

Code snippet

from monty.serialization import dumpfn

d = {(0, 0, 0): "hello"}
dumpfn(d, "test.json")

Log output

File ~\miniconda\envs\quacc\Lib\site-packages\monty\serialization.py:127,)    125     if "cls" not in kwargs:
    126         kwargs["cls"] = MontyEncoder
--> 127     fp.write(json.dumps(obj, *args, **kwargs))
    128 else:
    129     raise TypeError(f"Invalid format: {fmt}")

File ~\miniconda\envs\quacc\Lib\json\__init__.py:238, in dumps(obj, skipk)    232 if cls is None:
    233     cls = JSONEncoder
    234 return cls(
    235     skipkeys=skipkeys, ensure_ascii=ensure_ascii,
    236     check_circular=check_circular, allow_nan=allow_nan, indent=in,    237     separators=separators, default=default, sort_keys=sort_keys,
--> 238     **kw).encode(obj)

File ~\miniconda\envs\quacc\Lib\json\encoder.py:200, in JSONEncoder.encode(self, o)
    196         return encode_basestring(o)
    197 # This doesn't pass the iterator directly to ''.join() because the    198 # exceptions aren't as detailed.  The list call should be roughly
    199 # equivalent to the PySequence_Fast that ''.join() would do.
--> 200 chunks = self.iterencode(o, _one_shot=True)
    201 if not isinstance(chunks, (list, tuple)):
    202     chunks = list(chunks)

File ~\miniconda\envs\quacc\Lib\json\encoder.py:258, in JSONEncoder.itere)    253 else:
    254     _iterencode = _make_iterencode(
    255         markers, self.default, _encoder, self.indent, floatstr,
    256         self.key_separator, self.item_separator, self.sort_keys,
    257         self.skipkeys, _one_shot)
--> 258 return _iterencode(o, 0)

TypeError: keys must be str, int, float, bool or None, not tuple

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[Andrew-S-Rosen]

Probably easier to just jsanitize this one beforehand I suppose.