>>> a=(1,2,3,4)
>>> a+=(5,6,7)
>>> print(a)

>>> a=[1,2,3,4]
>>> a+=[5,6,7]
>>> print( a )

>>> a=(1,2,3,4)
>>> print(id(a))
>>> a+=(5,6,7)
>>> print(id(a))

>>> a=[1,2,3,4]
>>> print(id(a))
>>> a+=[5,6,7]
>>> print(id(a))

>>> a=(1,2,3,4)
>>> a=a+(5,6,7)

>>> a=[1,2,3,4]
>>> a.extend([5,6,7])

class PointMutable(object):
    def __init__(self, x, y):
        self.x=x
        self.y=y

    def __repr__(self):
        return "<Point(%d,%d)>"%(self.x,self.y)

    def __sub__(self, other):
        self.x-=other.x
        self.y-=other.y
        return self
    
    def __add__(self, other):
        self.x+=other.x
        self.y+=other.y
        return self

    def move(self, dx, dy):
        self.x+=dx
        self.y+=dy
        return self

>>> p1=PointMutable(1,1)
>>> p2=PointMutable(-1,1)
>>> print p1.move(1,1) - (p1+p2).move(2,2)

class PointInmutable(object):
    def __init__(self, x, y):
        self.x=x
        self.y=y

    def __repr__(self):
        return "<Point(%d,%d)>"%(self.x,self.y)

    def __sub__(self, other):
        return PointInmutable(self.x-other.x,self.y-other.y)
    
    def __add__(self, other):
        return PointInmutable(self.x+other.x,self.y+other.y)

    def move(self, dx, dy):
        return PointInmutable(self.x+dx,self.y+dy)

>>> p1=PointInmutable(1,1)
>>> p2=PointInmutable(-1,1)
>>> print p1.move(1,1) - (p1+p2).move(2,2)