CODEWITHSUNDEEP
pythonfunctionclassoopmethod-call
Steven
Steven

Reputation: 4383

How can I call a function within a class?

I have this code which calculates the distance between two coordinates. The two functions are both within the same class.

However, how do I call the function distToPoint in the function isNear?

class Coordinates:
    def distToPoint(self, p):
        """
        Use pythagoras to find distance
        (a^2 = b^2 + c^2)
        """
        ...

    def isNear(self, p):
        distToPoint(self, p)
        ...

Upvotes: 413

Views: 820784

Answers (4)

Soudip Das
Soudip Das

Reputation: 1

In the above scenario, you are trying to access a member method from another member method defined within the same class.

To achieve this you have to use the self keyword before distToPoint(self, p) like this:self.distToPoint(self, p) to invoke the distToPoint(self, p) method from isNear(self, p).

Hope this helps.

Upvotes: 0

cottontail
cottontail

Reputation: 23011

In the OP, distToPoint() and isNear() are both instance methods and as such, both take a reference to an instance (usually named self) as its first argument. When an instance method called directly from the instance, the reference is passed implicitly, so

self.distToPoint(p)

works.

If you want to call an overridden parent method from the child class, then super() could/should be used. In the following example, greet() method is defined in both Parent and Child classes and if you want to call Parent's greet(), the prescribed way is via super(), i.e. super().greet(). It's also possible to do it via the class name, i.e. Parent.greet(self) but there are many arguments against such hard-coding in favor of super() such as flexibility, the ability to use method resolution order correctly etc.

class Parent:
    def greet(self):
        print("greetings from Parent!")
        
    def parent_printer(self):
        print("this is parent printer")
        
class Child(Parent):
    def greet(self, parent=False):
        if parent:
            super().greet()                 # Parent's greet is called
        else:
            print("greetings from Child!")
        
    def printer(self, greet=True):
        if greet:
            self.greet()                    # Child's greet is called
        else:
            self.parent_printer()           # Parent's parent_printer is inherited
        
        
c = Child()
c.greet()                # greetings from Child!
c.greet(parent=True)     # greetings from Parent!
c.printer()              # greetings from Child!
c.printer(greet=False)   # this is parent printer

Upvotes: 2

Aleksi Torhamo
Aleksi Torhamo

Reputation: 6632

That doesn't work because distToPoint is inside your class, so you need to prefix it with the classname if you want to refer to it, like this: classname.distToPoint(self, p). You shouldn't do it like that, though. A better way to do it is to refer to the method directly through the class instance (which is the first argument of a class method), like so: self.distToPoint(p).

Upvotes: 83

Jeff Mercado
Jeff Mercado

Reputation: 134801

Since these are member functions, call it as a member function on the instance, self.

def isNear(self, p):
    self.distToPoint(p)
    ...

Upvotes: 640

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