How do I call a parent class's method from a child class in Python?

user_16513 0
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When creating a simple object hierarchy in Python, I'd like to be able to invoke methods of the parent class from a derived class. In Perl and Java, there is a keyword for this (super). In Perl, I might do this:

package Foo;

sub frotz {
    return "Bamf";
}

package Bar;
@ISA = qw(Foo);

sub frotz {
   my $str = SUPER::frotz();
   return uc($str);
}

In Python, it appears that I have to name the parent class explicitly from the child. In the example above, I'd have to do something like Foo::frotz().

This doesn't seem right since this behavior makes it hard to make deep hierarchies. If children need to know what class defined an inherited method, then all sorts of information pain is created.

Is this an actual limitation in python, a gap in my understanding or both?

object inheritance class oop python
16 Answers

Use the super() function:

class Foo(Bar):
    def baz(self, **kwargs):
        return super().baz(**kwargs)

For Python < 3, you must explicitly opt in to using new-style classes and use:

class Foo(Bar):
    def baz(self, arg):
        return super(Foo, self).baz(arg)
Adam_Rosenfield_95300

Python also has super as well:

super(type[, object-or-type])

Return a proxy object that delegates method calls to a parent or sibling class of type. This is useful for accessing inherited methods that have been overridden in a class. The search order is same as that used by getattr() except that the type itself is skipped.

Example: 

class A(object):     # deriving from 'object' declares A as a 'new-style-class'
    def foo(self):
        print "foo"

class B(A):
    def foo(self):
        super(B, self).foo()   # calls 'A.foo()'

myB = B()
myB.foo()
Jay_208400 
ImmediateParentClass.frotz(self)

will be just fine, whether the immediate parent class defined frotz itself or inherited it. super is only needed for proper support of multiple inheritance (and then it only works if every class uses it properly). In general, AnyClass.whatever is going to look up whatever in AnyClass's ancestors if AnyClass doesn't define/override it, and this holds true for "child class calling parent's method" as for any other occurrence!

user_958100

There's a super() in Python too. It's a bit wonky, because of Python's old- and new-style classes, but is quite commonly used e.g. in constructors:

class Foo(Bar):
    def __init__(self):
        super(Foo, self).__init__()
        self.baz = 5
user_568170

In this example cafec_param is a base class (parent class) and abc is a child class. abc calls the AWC method in the base class.

class cafec_param:

    def __init__(self,precip,pe,awc,nmonths):

        self.precip = precip
        self.pe = pe
        self.awc = awc
        self.nmonths = nmonths

    def AWC(self):

        if self.awc<254:
            Ss = self.awc
            Su = 0
            self.Ss=Ss
        else:
            Ss = 254; Su = self.awc-254
            self.Ss=Ss + Su   
        AWC = Ss + Su
        return self.Ss


    def test(self):
        return self.Ss
        #return self.Ss*4

class abc(cafec_param):
    def rr(self):
        return self.AWC()


ee=cafec_param('re',34,56,2)
dd=abc('re',34,56,2)
print(dd.rr())
print(ee.AWC())
print(ee.test())

Output

56

56

56
user_91101430 
class department:
    campus_name="attock"
    def printer(self):
        print(self.campus_name)

class CS_dept(department):
    def overr_CS(self):
        department.printer(self)
        print("i am child class1")

c=CS_dept()
c.overr_CS()
user_106698480

If you want to call the method of any class, you can simply call Class.method on any instance of the class. If your inheritance is relatively clean, this will work on instances of a child class too:

class Foo:
    def __init__(self, var):
        self.var = var
    
    def baz(self):
        return self.var

class Bar(Foo):
    pass

bar = Bar(1)
assert Foo.baz(bar) == 1
user_116098340 
class a(object):
    def my_hello(self):
        print "hello ravi"

class b(a):
    def my_hello(self):
    super(b,self).my_hello()
    print "hi"

obj = b()
obj.my_hello()
user_103003650
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