why can't I pickle a class containing this dispatch dictionary?

[jkn]

Hi All
    I'm clearly not understanding the 'can't pickle instancemethod
objects' error; can someone help me to understand, & maybe suggest a
workaround, (apart from the obvious if ... elif...).

I'm running Python 2.6 on an embedded system.

== testpickle.py ==
import pickle

class Test(object):
    def __init__(self):
        self.myDict = {
            1: self.tag1,
            2: self.tag2
            }
    def dispatch(self, v):
        try:
            self.myDict[v]()
        except KeyError:
            print "No corresponding dictionary entry!"
        #
    def tag1(self):
        print "one"
    def tag2(self):
        print "two"


t = Test()
t.dispatch(1)
t.dispatch(2)
t.dispatch(0)

fd = open("pickle.out", "w")
pickle.dump(t, fd)
fd.close()
# EOF

$ python testpickle.py
one
two
No corresponding dictionary entry!
Traceback (most recent call last):
  File "ptest.py", line 29, in <module>
    pickle.dump(t, fd)
  File "/usr/lib/python2.6/pickle.py", line 1362, in dump
    Pickler(file, protocol).dump(obj)
  File "/usr/lib/python2.6/pickle.py", line 224, in dump
    self.save(obj)
  File "/usr/lib/python2.6/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/lib/python2.6/pickle.py", line 419, in save_reduce
    save(state)
  File "/usr/lib/python2.6/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python2.6/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/usr/lib/python2.6/pickle.py", line 663, in _batch_setitems
    save(v)
  File "/usr/lib/python2.6/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python2.6/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/usr/lib/python2.6/pickle.py", line 663, in _batch_setitems
    save(v)
  File "/usr/lib/python2.6/pickle.py", line 306, in save
    rv = reduce(self.proto)
  File "/usr/lib/python2.6/copy_reg.py", line 70, in _reduce_ex
    raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle instancemethod objects
$


    Thanks
    J^n

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