Question

I want to define a new class that inherit the build in str type, and create a method that duplicates the string contents.

How do I get access to the string value assigned to the object of my new class ?

    class str_usr(str):
        def __new__(cls, arg):
            return str.__new__(cls, arg)
        def dub(self):
            # How to modify the string value in self ?
            self.<attr> = self.<attr> + self.<attr>

Thanks for any help 🙂

Answer 1

Strings in Python are immutable, so once you have one string, you can’t change its value. It’s almost the same as if you had a class derived from int, and then you added a method to change the value of the int.

You can of course return a new value:

class str_usr(str):
    def dup(self):
        return self + self # or 2 * self

s = str_usr("hi")
print s # prints hi
print s.dup() # print hihi