reinitialize an object with self.__init__(...)

Question

The only thing special about __init__ is that it is called automatically when an instance is created. Other than that it is a normal method, and it is safe to use it to set your object back to its initial state.

That being said, just because it is safe doesn't mean it is a good idea. Other people looking at your code might be confused by it, and it isn't difficult to do everything in a reset method (that __init__ can even call) to be more explicit about how the method is being used.

I would consider it a very bad practice - you should not __init__ manually (unless calling __init__ of the parent class). Also, passing object's data back to __init__ is somewhat strange.

Why not something like this:

class Book(object):
    def __init__(self,name,author):
        self.name = name
        self.author = author
        self.reset()

    def reset(self):
        self.copies = 5

I consider is not unsafe, I have used it and nothing strange happens in the memory, but take into account that attributes defined in other methods will not be reset. Consider for example:

class Dummy:
    def __init__(self):
        self.x = 4
    def plus_one(self):
        self.x += 1
    def define_other_variables(self):
        self.y = 3
    def reset(self):
        self.__init__()
D = Dummy()
print(D.x) # 4
# print(D.y) will raise an AttributeError
D.plus_one()
D.plus_one()
# D.y do not exist
D.define_other_variables()
# D.y exist
print(D.x) # 6
D.reset()
print(D.x) # 4
print(D.y) # 3, still exist!!

Then, just remember to define every object in the init function. you could consider bad practice for this reason but I still think is elegant.