I recently came across the following function: def generic_method(self, *args)

And I read that this means that one can access any class attributes by calling self.attribute_name without having to pass it into the method signature.

The full function read

class PacketContext:
    def __init__(self, capture_tstamp=None):
        self.capture_tstamp = capture_tstamp

def generic_method(self, *args): 
     self.context = PacketContext()

While I understand the first part, what does it mean by

without having to pass it into the method signature?

CodePudding user response：

As stated in the comments, the *args have nothing to do with the ability to access attributes with self.attribute_name.

The signature of a function, so to speak is the definition of the interaface the function offers. In other words: "What do you need to pass and what do you get in return?" Example:

def foo(int i, bool b) -> bool:
   return i > 5 or b

Here, the signature is "Give me an int i and a bool b and I'll return a bool.

The self argument is a little special. If you add the self argument to a function in Python, it indicates that this is an instance method. This means that the function requires a class to be instantiated before the method can be run on an the instance of an object. Example:

class MyClass:
    def __init__(self, instance_variable):
        self.instance_variable = instance_variable

    def my_method(self, *args): 
        print(self.instance_variable)

if __name__ == "__main__":
   instance_of_my_class = MyClass(instance_variable="Great")

   # Notice how my_method is called
   instance_of_my_class.my_method()

   # Internally, Python does the following when it encounters the line above
   my_method(self=instance_of_my_class)

Now what they (to my understanding) mean by

without having to pass it into the method signature?

is that you didn't have to specify instance_variable in the signature of my_method. Because it is an instance method, you can access all attributes of the instance via self.