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copied!<p>A new feature was added to Python 2.7.3 that allows for <em>dynamically</em> created classes to be pickled. See <a href="http://bugs.python.org/issue7689" rel="nofollow">issue 7689</a>:</p> <blockquote> <p>Currently, it's impossible to use the usual pickle mechanisms to pickle a dynamically created class, even if the user requests a different pickling mechanism via copy_reg. The attached patch makes this customization possible by simply transposing two blocks of code. </p> </blockquote> <p>and</p> <blockquote> <p>The copy_reg module exists to handle custom pickling of objects, which is exactly what's needed here. However, the code from <strike><a href="http://bugs.python.org/issue494904" rel="nofollow">#494904</a></strike> that checks for instances of a metaclass does this *just before* it looks at the copy_reg dispatch table. The patches just reorder these tests in pickle.py and cPickle.c, so that one can register a custom pickler for instances of a metaclass. </p> </blockquote> <p>And from the <a href="http://hg.python.org/cpython/file/d46c1973d3c4/Misc/NEWS#l328" rel="nofollow">2.7.3 changelog</a>:</p> <blockquote> <p>Issue #7689: Allow pickling of dynamically created classes when their metaclass is registered with copy_reg. Patch by Nicolas M. Thiéry and Craig Citro.</p> </blockquote> <p>The only way around this for Python 2.6 is to port the <code>pickle.py</code> module over to that version. You could try to just bundle the 2.7.3 <code>pickle.py</code> module with 2.6, as a pure Python implementation it should Just Work.</p> <p>Alternatively, monkey-patch the <code>pickle.Pickler.save</code> method:</p> <pre><code>from copy_reg import dispatch_table from types import TypeType, StringType, TupleType from pickle import Pickler, PicklingError def pickler_save(self, obj): # Check for persistent id (defined by a subclass) pid = self.persistent_id(obj) if pid: self.save_pers(pid) return # Check the memo x = self.memo.get(id(obj)) if x: self.write(self.get(x[0])) return # Check the type dispatch table t = type(obj) f = self.dispatch.get(t) if f: f(self, obj) # Call unbound method with explicit self return # Check copy_reg.dispatch_table reduce = dispatch_table.get(t) if reduce: rv = reduce(obj) else: # Check for a class with a custom metaclass; treat as regular class try: issc = issubclass(t, TypeType) except TypeError: # t is not a class (old Boost; see SF #502085) issc = 0 if issc: self.save_global(obj) return # Check for a __reduce_ex__ method, fall back to __reduce__ reduce = getattr(obj, "__reduce_ex__", None) if reduce: rv = reduce(self.proto) else: reduce = getattr(obj, "__reduce__", None) if reduce: rv = reduce() else: raise PicklingError("Can't pickle %r object: %r" % (t.__name__, obj)) # Check for string returned by reduce(), meaning "save as global" if type(rv) is StringType: self.save_global(obj, rv) return # Assert that reduce() returned a tuple if type(rv) is not TupleType: raise PicklingError("%s must return string or tuple" % reduce) # Assert that it returned an appropriately sized tuple l = len(rv) if not (2 <= l <= 5): raise PicklingError("Tuple returned by %s must have " "two to five elements" % reduce) # Save the reduce() output and finally memoize the object self.save_reduce(obj=obj, *rv) Pickler.save = pickler_save </code></pre> <p>With the above monkey patch, your example works on Python 2.6.8:</p> <pre><code>>>> pickle.dumps(B) Hey there 'c__main__\nB\np0\n.' </code></pre>

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