[Python] Flask and Flask Session, using a ad-hoc decode/encode (eg. with msgpack)

I would like to explicitly tell to flask-session how to encode / decode some instances from classes that are specific to my application. (This is legacy code, I can not change the classes).

For example I have some classes looking like this:

class Subclass(metaclass=abc.ABCMeta):
def __init__(self, before=None, next=None, nested_steps=None):
self.before = before
self.next = next
self.nested_steps = nested_steps or []


class MyClass1(Subclass):
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.number = 1
self.name = "myclass1"

class MyClass2(Subclass):
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.number = 2
self.name = "myclass2"
self.nested_steps = [MyClass1()]

class OverallClass:
def __init__(self):
self.class1 = MyClass1()
self.class2 = MyClass2(before=self.class1)
self.class1.next = self.class2
self.class2.nested_steps = [self.class1]
self.steps = [self.class1, self.class2]



I can encode /decode them myself and even use msgpack for this, following the documentation:

thedict = {"id": 1, "obj": OverallClass()}
packed = msgpack.packb(thedict, default=encode_internalClass)
unpacked = msgpack.unpackb(packed, object_hook=decode_internalClass)


This works fine for standalone serialization and deserialization. However, I am struggling to integrate this with flask_session. I think I need to overwrite the serializer of flask_session to use those encode_internalClass and decode_internalClass within my app and with jinja2 templates.

I would need this because I am using for example :


@app.route("/save_object_live")
def save_object_live():
# Create an instance of our internal class
overallclass = OverallClass()
# Serialize the object and store it in the session
session["test_local"] = overallclass
flash("Object saved in session")
return redirect(url_for("home"))


@app.route("/load_object_live")
def load_object_live():
# Deserialize the object from the session
serialized_data = session.get("test_local")
if serialized_data:
flash("Object loaded from session")
return redirect(url_for("home"))
else:
flash("No object found in session")
return redirect(url_for("home"))





The full stack of the application is flask, flask-session, jinja2 and mongodb.

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