[Sqlalchemy-tickets] Issue #3297: Custom MutableSet (similar to MutableDict) not pickling (zzzeek/sqlalchemy)

[Eoghan M. <iss...@bi...>]

New issue 3297: Custom MutableSet (similar to MutableDict) not pickling
https://bitbucket.org/zzzeek/sqlalchemy/issue/3297/custom-mutableset-similar-to-mutabledict

Eoghan Murray:

I've created a MutableSet class, closely following the MutableDict class in ext.mutable.

Unfortunately it doesn't pickle correctly and I can't figure out what the problem is.

```
#!python

from sqlalchemy import *
from sqlalchemy.ext.mutable import Mutable, MutableDict
test_table = Table('test_table, metadata,
    Column('test_pk', String(40), primary_key=True),
    Column('as_dict', MutableDict.as_mutable(JsonType)),
    Column('as_set', MutableSet.as_mutable(JsonType))
```


 my error message after using pickle.dumps on an object that contains the MutableSet column.
Note the 'remove' function mentioned in the error is to do with  _parents WeakRef rather than MutableSet.remove)


```
#!python
  File "/usr/lib/python2.7/pickle.py", line 748, in save_global
    (obj, module, name))
PicklingError: Can't pickle <function remove at 0xb48a041c>: it's not found as weakref.remove
```

And the MutableSet class (and JsonType supporting class - included for completeness)

```
#!python

class MutableSet(Mutable, set):
    @classmethod
    def coerce(cls, key, value):
        "Convert plain sets to MutableSet."

        if not isinstance(value, MutableSet):
            if isinstance(value, set):
                return MutableSet(value)
            elif isinstance(value, dict):
                return MutableDict(value)
            # this call will raise ValueError
            return Mutable.coerce(key, value)
        else:
            return value
    def __getstate__(self):
        return set(self)
    def __setstate__(self, state):
        self.update(state)
    def update(self, *args):
        set.update(self, *args, **kwargs)
        self.changed()
    def intersection_update(self, *args):
        set.intersection_update(self, *args)
        self.changed()
    def difference_update(self, *args):
        set.difference_update(self, *args)
        self.changed()
    def symmetric_difference_update(self, *args):
        set.symmetric_difference_update(self, *args)
        self.changed()
    def add(self, elem):
        set.add(self, elem)
        self.changed()
    def remove(self, elem):
        set.remove(self, elem)
        self.changed()
    def discard(self, elem):
        set.discard(self, elem)
        self.changed()
    def pop(self):
        set.pop(self)
        self.changed()
    def clear(self):
        set.clear(self)
        self.changed()
```


```
#!python

class JsonType(types.TypeDecorator):
    impl = types.Unicode

    def process_bind_param(self, value, engine):
        import jsonpickle
        if isinstance(value, MutableList):
            value = [v for v in value]
        if isinstance(value, MutableDict):
            value = dict(value)
        if isinstance(value, MutableSet):
            value = set(value)
        return unicode(jsonpickle.encode(value))

    def process_result_value(self, value, engine):
        import jsonpickle
        if value:
            return jsonpickle.decode(value)
        else:
            return {}

    def copy_value(self, value):
        return deepcopy(value)

    def compare_values(self, x, y):
        return x == y

```

Responsible: zzzeek