'SingleQubitCliffordGate' object has no attribute '__name__'

[epelaaez]

Description of the issue
I'm trying to define a noise model with Clifford gates, and then serialize it. However, I get an error when trying to serialize it using cirq.to_json.

How to reproduce the issue

A simplified version of my noise model is the following.

p_x, p_y, p_z = 0.1, 0.1, 0.1
pauli_error_rates = {"X": p_x, "Y": p_y, "Z": p_z, "I": 1 - (p_x + p_y + p_z)}
qubits = cirq.LineQubit.range(1)
cliff = cirq.SingleQubitCliffordGate.from_xz_map((cirq.X, False), (cirq.Z, False))
ops_added = {
    cirq.OpIdentifier(cliff, qubits[0]): cirq.asymmetric_depolarize(error_probabilities=pauli_error_rates)(qubits[0])
}

Then, I do the following to serialize it.

model = cirq.devices.InsertionNoiseModel(ops_added, prepend=True, require_physical_tag=False)
cirq.to_json(model)

And I get the following.

AttributeError: 'SingleQubitCliffordGate' object has no attribute '__name__'

(full log below)

I also noticed the same happens when I use a cirq.CZ gate.

AttributeError                            Traceback (most recent call last)
Cell In[30], line 1
----> 1 cirq.to_json(model)

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:613, in to_json(obj, file_or_fn, indent, separators, cls)
    583 def to_json(
    584     obj: Any,
    585     file_or_fn: Union[None, IO, pathlib.Path, str] = None,
   (...)
    589     cls: Type[json.JSONEncoder] = CirqEncoder,
    590 ) -> Optional[str]:
    591     """Write a JSON file containing a representation of obj.
    592 
    593     The object may be a cirq object or have data members that are cirq
   (...)
    611             to your classes rather than overriding this default.
    612     """
--> 613     if has_serializable_by_keys(obj):
    614         obj = _ContextualSerialization(obj)
    616         class ContextualEncoder(cls):  # type: ignore

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:430, in has_serializable_by_keys(obj)
    428 json_dict = getattr(obj, '_json_dict_', lambda: None)()
    429 if isinstance(json_dict, Dict):
--> 430     return any(has_serializable_by_keys(v) for v in json_dict.values())
    432 # Handle primitive container types.
    433 if isinstance(obj, Dict):

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:430, in <genexpr>(.0)
    428 json_dict = getattr(obj, '_json_dict_', lambda: None)()
    429 if isinstance(json_dict, Dict):
--> 430     return any(has_serializable_by_keys(v) for v in json_dict.values())
    432 # Handle primitive container types.
    433 if isinstance(obj, Dict):

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:441, in has_serializable_by_keys(obj)
    436 if hasattr(obj, '__iter__') and not isinstance(obj, str):
    437     # Return False on TypeError because some numpy values
    438     # (like np.array(1)) have iterable methods
    439     # yet return a TypeError when there is an attempt to iterate over them
    440     try:
--> 441         return any(has_serializable_by_keys(elem) for elem in obj)
    442     except TypeError:
    443         return False

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:441, in <genexpr>(.0)
    436 if hasattr(obj, '__iter__') and not isinstance(obj, str):
    437     # Return False on TypeError because some numpy values
    438     # (like np.array(1)) have iterable methods
    439     # yet return a TypeError when there is an attempt to iterate over them
    440     try:
--> 441         return any(has_serializable_by_keys(elem) for elem in obj)
    442     except TypeError:
    443         return False

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:441, in has_serializable_by_keys(obj)
    436 if hasattr(obj, '__iter__') and not isinstance(obj, str):
    437     # Return False on TypeError because some numpy values
    438     # (like np.array(1)) have iterable methods
    439     # yet return a TypeError when there is an attempt to iterate over them
    440     try:
--> 441         return any(has_serializable_by_keys(elem) for elem in obj)
    442     except TypeError:
    443         return False

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:441, in <genexpr>(.0)
    436 if hasattr(obj, '__iter__') and not isinstance(obj, str):
    437     # Return False on TypeError because some numpy values
    438     # (like np.array(1)) have iterable methods
    439     # yet return a TypeError when there is an attempt to iterate over them
    440     try:
--> 441         return any(has_serializable_by_keys(elem) for elem in obj)
    442     except TypeError:
    443         return False

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:428, in has_serializable_by_keys(obj)
    426 if isinstance(obj, SerializableByKey):
    427     return True
--> 428 json_dict = getattr(obj, '_json_dict_', lambda: None)()
    429 if isinstance(json_dict, Dict):
    430     return any(has_serializable_by_keys(v) for v in json_dict.values())

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/devices/noise_utils.py:89, in OpIdentifier._json_dict_(self)
     88 def _json_dict_(self) -> Dict[str, Any]:
---> 89     gate_json = protocols.json_cirq_type(self._gate_type)
     90     return {'gate_type': gate_json, 'qubits': self._qubits}

File /Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/cirq/protocols/json_serialization.py:506, in json_cirq_type(type_obj)
    504 if namespace:
    505     return f'{namespace}.{type_obj.__name__}'
--> 506 return type_obj.__name__

AttributeError: 'SingleQubitCliffordGate' object has no attribute '__name__'

Cirq version
1.3.0.dev20230915001934

[vtomole]

@epelaaez Do you want to work on this?

[epelaaez]

Yes, I can look into it

It seems like the problem here is that when defining a gate as follows:

gate = cirq.SingleQubitCliffordGate.from_xz_map((cirq.X, False), (cirq.Z, False))

Doing gate.__name__ returns the error I'm experiencing, but doing gate.__class__.__name__ returns 'SingleQubitCliffordGate', which I think is the output we want (can you confirm this?)

[vtomole]

which I think is the output we want

Yep

[epelaaez]

I found that doing

ops_added = { 
    cliff(qubits[0]): cirq.asymmetric_depolarize(error_probabilities=pauli_error_rates)(qubits[0]) 
}

solves the problem.

The issue is that OpIdentifier._json_dict_ calls protocols.json_cirq_type(self._gate_type) and this is where the '__name__' is not found. This could be fixed by doing something like

try:
    return type_obj.__name__
except AttributeError:
    return type_obj.__class__.__name__

but then I get

{
  "cirq_type": "InsertionNoiseModel",
  "ops_added": [
    [
      {
        "cirq_type": "OpIdentifier",
        "gate_type": "SingleQubitCliffordGate",
        "qubits": [
          {
            "cirq_type": "LineQubit",
            "x": 0
          }
        ]
      },
      {
        "cirq_type": "GateOperation",
        "gate": {
          "cirq_type": "AsymmetricDepolarizingChannel",
          "error_probabilities": {
            "X": 0.1,
            "Y": 0.1,
            "Z": 0.1,
            "I": 0.7
          }
        },
        "qubits": [
          {
            "cirq_type": "LineQubit",
            "x": 0
          }
        ]
      }
    ]
  ],
  "prepend": true,
  "require_physical_tag": false
} 

which loses information about the specific Clifford gate I'm using in my model. I think this is the intended behavior of OpIdentifier though, as it takes as an argument gate_type: Type['cirq.Gate'] and not a specific gate. Since it seems like I can get away with not using OpIdentifier when using particular gates, and this looks like intended behavior, I think this could be closed (wdyt @vtomole)?

[vtomole]

So, it looks like OpIdentifier can't be json serializable for some inputs?

[epelaaez]

Yes, I think that's the issue. At least that the specificity of certain inputs is lost when serializing it.

[vtomole]

Okay, sounds like a bug that we can fix as part of this.