Regarding multiple parent inheritance, when I call the super
.__init__
, why doesn't parent2's __init__
function get called? Thanks.
class parent(object):
var1=1
var2=2
def __init__(self,x=1,y=2):
self.var1=x
self.var2=y
class parent2(object):
var4=11
var5=12
def __init__(self,x=3,y=4):
self.var4=x
self.var5=y
def parprint(self):
print self.var4
print self.var5
class child(parent, parent2):
var3=5
def __init__(self,x,y):
super(child, self).__init__(x,y)
childobject = child(9,10)
print childobject.var1
print childobject.var2
print childobject.var3
childobject.parprint()
Output is
9
10
5
11
12
If you want to use super
in child
to call parent.__init__
and parent2._init__
, then both parent __init__
s must also call super
:
class parent(Base):
def __init__(self,x=1,y=2):
super(parent,self).__init__(x,y)
class parent2(Base):
def __init__(self,x=3,y=4):
super(parent2,self).__init__(x,y)
See "Python super method and calling alternatives" for more details on the sequence of calls to __init__
caused by using super
.
class Base(object):
def __init__(self,*args):
pass
class parent(Base):
var1=1
var2=2
def __init__(self,x=1,y=2):
super(parent,self).__init__(x,y)
self.var1=x
self.var2=y
class parent2(Base):
var4=11
var5=12
def __init__(self,x=3,y=4):
super(parent2,self).__init__(x,y)
self.var4=x
self.var5=y
def parprint(self):
print self.var4
print self.var5
class child(parent, parent2):
var3=5
def __init__(self,x,y):
super(child, self).__init__(x,y)
childobject = child(9,10)
print childobject.var1
print childobject.var2
print childobject.var3
childobject.parprint()
You might be wondering, "Why use Base
?". If parent
and parent2
had inherited directly from object
, then
super(parent2,self).__init__(x,y)
would call object.__init__(x,y)
. That raises a TypeError
since object.__init__()
takes no parameters.
To workaround this issue, you can make a class Base
which accepts arguments to __init__
but does not pass them on to object.__init__
. With parent
and parent2
inheriting from Base
, you avoid the TypeError
.