Can I dynamically convert an instance of one class to another?

Question

I have a class that describe chess pieces. I make for all type piece in the Board a class for example Pawn, Queen, keen, etc... I have a trouble in Pawn class I want to convert to Queen or other object that has a class (when pawn goto 8th row then convert to something another) how can I do this ?

class Pawn:     def __init__(self ,x ,y):         self.x = x         self.y = y     def move(self ,unit=1):         if self.y ==7 :             self.y += 1             what = raw_input("queen/rook/knight/bishop/(Q,R,K,B)?")             # There is most be changed that may be convert to:             # Queen ,knight ,bishop ,rook         if self.y != 2 and unit == 2:             print ("not accesible!!")         elif self.y ==2 and unit == 2:             self.y += 2         elif unit == 1:             self.y += 1         else:             print("can`t move over there") 

Answer 1

It is actually possible to assign to self.__class__ in Python, but you really have to know what you're doing. The two classes have to be compatible in some ways (both are user-defined classes, both are either old-style or new-style, and I'm not sure about the use of __slots__). Also, if you do pawn.__class__ = Queen, the pawn object will not have been constructed by the Queen constructor, so expected instance attributes might not be there etc.

An alternative would be a sort of copy constructor like this:

class ChessPiece(object):   @classmethod   def from_other_piece(cls, other_piece):     return cls(other_piece.x, other_piece.y) 

Edit: See also Assigning to an instance's __class__ attribute in Python