Deque with JSONDisk throws TypeError: a bytes-like object is required, not 'int'

[Marcus Hoffmann]

I tried using a Deque like this:

Deque.fromcache(Cache(eviction_policy="none", disk=JSONDisk)) and while I'm not yet entirely sure if that's a useful thing (I guess some of the serialization caveats also apply to Deque's even if there's no key to serialize?) it probably shouldn't crash like this:

>>> deque = Deque.fromcache(Cache(eviction_policy="none", disk=JSONDisk))
>>> deque += range(200)
>>> deque[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/marcus/.pyenv/versions/3.10.7/lib/python3.10/site-packages/diskcache/persistent.py", line 204, in __getitem__
    return self._index(index, self._cache.__getitem__)
  File "/home/marcus/.pyenv/versions/3.10.7/lib/python3.10/site-packages/diskcache/persistent.py", line 161, in _index
    for key in self._cache.iterkeys():
  File "/home/marcus/.pyenv/versions/3.10.7/lib/python3.10/site-packages/diskcache/core.py", line 2252, in iterkeys
    yield _disk_get(key, raw)
  File "/home/marcus/.pyenv/versions/3.10.7/lib/python3.10/site-packages/diskcache/core.py", line 360, in get
    return json.loads(zlib.decompress(data).decode('utf-8'))
TypeError: a bytes-like object is required, not 'int'

[Grant Jenks]

That is a bug. Unfortunately, it doesn't have a great fix.

Deque uses the Cache's push() and pull() API which uses special cache keys that don't play nice with the key-serialization done in JSONDisk.

Here's the workaround:

In [6]: class JSONDiskValue(dc.JSONDisk):
   ...:     put = dc.Disk.put
   ...:     get = dc.Disk.get

In [7]: deque = dc.Deque.fromcache(dc.Cache(eviction_policy="none", disk=JSONDiskValue))
In [11]: deque += range(200)
In [12]: deque[0]
Out[12]: 0