Beaker error: copy.deepcopy( session ) produces "AttributeError: 'Morsel' object has no attribute 'encode'"

gistfile1.txt

Traceback (most recent call last):
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid_debugtoolbar-1.0.4-py2.7.egg/pyramid_debugtoolbar/panels/performance.py", line 55, in resource_timer_handler
    result = handler(request)
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid/tweens.py", line 21, in excview_tween
    response = handler(request)
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid/router.py", line 161, in handle_request
    response = view_callable(context, request)
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid/config/views.py", line 235, in _secured_view
    result = _permitted(context, request)
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid/config/views.py", line 231, in _permitted
    principals = self.authn_policy.effective_principals(request)
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid/authentication.py", line 155, in effective_principals
    groups = self.callback(userid, request)
  File "/Users/me/MyProject/myproject/lib/security.py", line 38, in groupfinder
    if request.user:
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid/decorator.py", line 39, in __get__
    val = self.wrapped(inst)
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/pyramid/util.py", line 50, in <lambda>
    fn = lambda this: callable(this)
  File "/Users/me/MyProject/myproject/lib/security.py", line 60, in returnUser
    myDoc = copy.deepcopy(session) if session and session.get('GUID') == u_id else None
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 190, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 334, in _reconstruct
    state = deepcopy(state, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 163, in deepcopy
    y = copier(x, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 257, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 190, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 334, in _reconstruct
    state = deepcopy(state, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 163, in deepcopy
    y = copier(x, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 257, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 190, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy.py", line 358, in _reconstruct
    y[key] = value
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/Cookie.py", line 591, in __setitem__
    rval, cval = self.value_encode(value)
  File "/Users/me/.virtualenvs/myproject/lib/python2.7/site-packages/beaker/session.py", line 70, in value_encode
    sig = HMAC.new(self.secret, val.encode('UTF-8'), SHA1).hexdigest()
AttributeError: 'Morsel' object has no attribute 'encode'