pythonclassrecursion

Can a class contain an instance of itself as a data container?

Can a python class contain an instance of itself as a data container may look like this?

class A:
    def __init__(self, val):
        self.a = A(val)
        self.val = val

aa = A(2) 
#this will cause RuntimeError: maximum recursion depth exceeded

My purpose is using this class as a data container contain a copy inside if it when it be inited to reduce the deepcopy action. It may used as an "undo" chain give a chance to get the init val's value when it's necessary.

Is it possible for such an action?

Solution

  • This won't work, for the reason already given:

    1. Python sees A(2) and calls A.__init__.
    2. A.__init__ calls A(val).
    3. A(val) calls A.__init__.
    4. GOTO 2

    I assume you're doing this so that you have a log of what val has been; that is, if sometime later you decide that you want val to be 3 instead, you don't throw away the original value 2. How about:

    Code

    class A( object ):
    @property
    def val( self ):
        return self.history[ -1 ]

    @val.setter
    def val( self, value ):
        self.history.append( value )

    def __init__( self, val ):
        self.history = [ ]
        self.val = val

    Explanation