create custom namedtuple type with extra features

Question

I\'d like to create my own type of build-in namedtuple that has some extra features. Let\'s say we create a class:

from collections import namedtuple
MyClass         


        

Answer 1

namedtuple isn't a class, as you note; it's a function. But it's a function that returns a class. Thus, you can use the result of the namedtuple call as a parent class.

Since it is immutable, a namedtuple is initialized in __new__ rather in in __init__.

So something like this, perhaps:

MyTuple = namedtuple('MyTuple', 'field1 field2')

class MyClass(MyTuple):
    def __new__(cls, field1, field2):
        if not isinstance(field1, int):
            raise TypeError("field1 must be integer")
        # accept int or float for field2 and convert int to float
        if not isinstance(field1, (int, float)):
            raise TypeError("field2 must be float")
        return MyTuple.__new__(cls, field1, float(field2))