Reason why xrange is not inheritable in Python?

Question

I was trying to inherit xrange to enable the target object behaviors of an integer list (iterable and in operator support). But I got the following error message:

TypeError: Error when calling the metaclass bases
    type 'xrange' is not an acceptable base type

What's special of xrange?

Also, probably not related to that question, I noticed xrange has not method __contains__. For in operation, my basic knowledge is, a in A is equivalent to A.contains(a). Am I wrong, or xrange is something different?

I don't know if I should paste these as two separated questions. Appologize ahead.

Answer 1

xrange is implemented in C. As you can see in Tim Peters' post, there should be a convincing use case in order to justify the extra effort needed to allow subclassing of it.