Python Methods

Summary: in this tutorial, you’ll learn about Python methods and the differences between functions and methods.

Introduction to the Python methods #

By definition, a method is a function that is bound to an instance of a class. This tutorial helps you understand how it works under the hood.

The following defines a Request class that contains a function send():

class Request:
    def send():
        print('Sent')Copy

And you can call the send() function via the Request class like this:

Request.send() # SentCopy

The send() is a function object, which is an instance of the function class as shown in the following output:

print(Request.send)Copy

Output:

<function Request.send at 0x00000276F9E00310>Copy

The type of the send is function:

print(type(Request.send))Copy

Output:

<class 'function'>Copy

The following creates a new instance of the Request class:

http_request = Request()Copy

If you display the http_request.send, it’ll return a bound method object:

print(http_request.send)Copy

Output:

<bound method Request.send of <__main__.Request object at 0x00000104B6C3D580>>Copy

So the http_request.send is not a function like Request.send. The following checks if the Request.send is the same object as http_request.send. It’ll returns False as expected:

print(type(Request.send) is type(http_request.send))Copy

The reason is that the type of the Request.send is function while the type of the http_request.send is method, as shown below:

print(type(http_request.send))  # <class 'method'>
print(type(Request.send))  # <class 'function'>Copy

So when you define a function inside a class, it’s purely a function. However, when you access that function via an object, the function becomes a method.

Therefore, a method is a function that is bound to an instance of a class.

If you call the send() function via the http_request object, you’ll get a TypeError as follows:

http_request.send()Copy

Error:

TypeError: send() takes 0 positional arguments but 1 was givenCopy

Because the http_request.send is a method that is bound to the http_request object, Python always implicitly passes the object to the method as the first argument.

The following redefines the Request class where the send function accepts a list of arguments:

class Request:
    def send(*args):
        print('Sent', args)Copy

The following calls the send function from the Request class:

Request.send()Copy

Output:

Sent ()Copy

The send() function doesn’t receive any arguments.

However, if you call the send() function from an instance of the Request class, the args is not empty:

http_request.send()Copy

Output:

Sent (<__main__.Request object at 0x000001374AF4D580>,)Copy

In this case, the send() method receives an object which is the http_request, which is the object that it is bound to.

The following illustrates that the object that calls the send() method is the one that Python implicitly passes into the method as the first argument:

print(hex(id(http_request)))
http_request.send()Copy

Output:

0x1ee3a74d580
Sent (<__main__.Request object at 0x000001EE3A74D580>,)Copy

The http_request object is the same as the one Python passes to the send() method as the first argument because they have the same memory address. In other words, you can access the instance of the class as the first argument inside the send() method:

The following method call:

http_request.send()Copy

is equivalent to the following function call:

Request.send(http_request)Copy

For this reason, a method of an object always has the object as the first argument. By convention, it is called self:

class Request:
    def send(self):
        print('Sent', self)Copy

If you have worked with other programming languages such as Java or C#, the self is the same as the this object.

Summary #

• When you define a function inside a class, it’s purely a function. However, when you call the function via an instance of a class, the function becomes a method. Therefore, a method is a function that is bound to an instance of a class.
• A method is an instance of the method class.
• A method has the first argument (self) as the object to which it is bound.
• Python automatically passes the bound object to the method as the first argument. By convention, its name is self.

Quiz #