Pickling Robustly

[jepler epler]

On 21 Apr 2000 14:06:28 -0500, Glyph Lefkowitz
 <glyph at twistedmatrix.com> wrote:
>Perhaps I should ask this question in a different way.  How does
>Pickle tell if an object is pickleable or not?  Is there some
>pickle.ispicklable method I could refer to?

If you have control over the object hierarchy, why not use this
'unpicklable mixin' and convenience functions I just tossed together:

import pickle, UserList

class Unpicklable:
	def __getinitargs__(self):
		raise Unpicklable
		
def ispicklable(a):
	"""This tests if a can be pickled (by actually trying to do so)"""
	try:
		pickle.dumps(a)
	except Unpicklable:
		return 0
	return 1

def ispicklableinstance(a):
	"""Note that this function does not tell whether a ultimately
contains an unpicklable instance. But at least it's a simple test.""
	return isinstance(a, Unpicklable)

def ispicklableclass(A):
	"""Note that this function does not tell whether an instance
might ultimately be unpicklable due to something nested inside it."""
	return issubclass(a, Unpicklable)

if __name__=='__main__':
	class UserListU(UserList.UserList, Unpicklable): pass

	x = UserList.UserList([1,2,3])
	print pickle.dumps(x)

	y = UserListU([1,2,3])
	print pickle.dumps(y)  # This will cause an exception

Jeff