For the life of me I haven't been able to find any example of this for Python.
Say I have a class Person, and I want to serialize and deserialize an object from that class.
class Person:
def __init__(self, n, b):
self._name = n
self._born = b
@property
def name(self):
return self._name
@property
def born(self):
return self._born
def __str__(self):
return f"{self.name} was born in {self.born.isoformat()}"
p1 = Person("Baltasar", datetime(1919, 7, 1))
Now, I want to serialize that nice Person object, and I want to support datetime objects. So I wrote a custom serializer:
class JSONCoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj, datetime):
return { "__class__": "datetime",
"y": obj.year,
"month": obj.month,
"d": obj.day,
"h": obj.hour,
"minute": obj.minute,
"s": obj.second }
return json.JSONEncoder.default(self, obj)
The purpose is to be able to support a couple of types, including datetime.
Now comes the time to deserialize. I had to write a custome deserializer to match the serializer. Here it is:
class JSONDCoder(json.JSONDecoder):
def __init__(self):
json.JSONDecoder.__init__(self, object_hook=JSONDCoder.from_dict)
@staticmethod
def from_dict(d):
if d.get("__class__") == "datetime":
return datetime(d["y"], d["month"], d["d"],
d["h"], d["minute"], d["s"])
If I trigger:
coder = JSONCoder()
s = coder.encode(p1.__dict__)
print("Encoded: " s)
dcoder = JSONDCoder()
d = dcoder.decode(s)
print("Decoded: " str(d))
I obtain the following output:
Encoded: {"_name": "Baltasar", "_born": {"__class__": "datetime", "y": 1919, "month": 7, "d": 0, "h": 0, "minute": 0, "s": 0}}
Decoded: None
...
The only way to obtain anything apart from None, is to modify the decoder and change it to:
class JSONDCoder(json.JSONDecoder):
def __init__(self):
json.JSONDecoder.__init__(self, object_hook=JSONDCoder.from_dict)
@staticmethod
def from_dict(d):
if d.get("__class__") == "datetime":
return d
Whatever other option makes it to return None, as shown above.
How can I have my custom decoder so it supports datetime types?
CodePudding user response:
You simply forgot to add a return statement at the end of the from_dict method.
class JSONDCoder(json.JSONDecoder):
def __init__(self):
json.JSONDecoder.__init__(self, object_hook=JSONDCoder.from_dict)
@staticmethod
def from_dict(d):
if d.get("__class__") == "datetime":
return datetime(d["y"], d["month"], d["d"],
d["h"], d["minute"], d["s"])
return d
This definition should work, the output for me is the following:
Encoded: {"_name": "Baltasar", "_born": {"__class__": "datetime", "y": 1919, "month": 7, "d": 1, "h": 0, "minute": 0, "s": 0}}
Decoded: {'_name': 'Baltasar', '_born': datetime.datetime(1919, 7, 1, 0, 0)}
Let me know if it was what you were looking for.