3.14.5.1 Pickling and unpickling normal class
instances
When a pickled class instance is unpickled, its __init__()
method is normally not invoked. If it is desirable that the
__init__() method be called on unpickling, a class can define
a method __getinitargs__(), which should return a
tuple containing the arguments to be passed to the class
constructor (i.e. __init__()). The
__getinitargs__() method is called at
pickle time; the tuple it returns is incorporated in the pickle for
the instance.
Classes can further influence how their instances are pickled; if the
class defines the method __getstate__(), it is called and the
return state is pickled as the contents for the instance, instead of
the contents of the instance's dictionary. If there is no
__getstate__() method, the instance's __dict__ is
pickled.
Upon unpickling, if the class also defines the method
__setstate__(), it is called with the unpickled
state3.7. If there is no __setstate__() method, the
pickled state must be a dictionary and its items are assigned to the
new instance's dictionary. If a class defines both
__getstate__() and __setstate__(), the state object
needn't be a dictionary and these methods can do what they
want.3.8
Warning:
For new-style classes, if __getstate__() returns a false
value, the __setstate__() method will not be called.
