Implementation of NoneType, Reasons and Details

Question

I recently read somewhere that the special value None in python is a singleton object of its own class, specifically NoneType. This explained a lot

Answer 1

Why is n the exact same Object as None?

Many immutable objects in Python are interned including None, smaller ints, and many strings.

Demo:

>>> s1='abc'
>>> s2='def'
>>> s3='abc'
>>> id(s1)
4540177408
>>> id(s3)
4540177408    # Note: same as s1
>>> x=1
>>> y=2
>>> z=1
>>> id(x)
4538711696
>>> id(z)
4538711696    # Note: same as x

Why was the language designed such that n is the exact same Object as None?

See above -- speed, efficiency, lack of ambiguity and memory usage among other reasons to intern immutable objects.

How would one even implement this behavior in python?

Among other ways, you can override __new__ to return the same object:

class Singleton(object):
    _instance = None
    def __new__(cls, *args, **kwargs):
        if not cls._instance:
            cls._instance = super(Singleton, cls).__new__(
                                cls, *args, **kwargs)
        return cls._instance

For strings, you can call intern on Python 2 or sys.intern on Python 3