Always prefer xrange above range?

Question

The range creates a list in memory of the number of elements defined by the programmer. The xrange has more performance, I do not know if in all cases, since it does not end up generating a list.

I must always wear xrange above range? There are cases where the use of range is more advantageous than the use of xrange?

Answer 1

In fact, in Python 3 there is no longer the equivalent of the "range" of Python 2 - the "range" is now what used to be the old xrange.

But in Python 2 code, yes, there is no reason to use the normal "range". The "range" (from Python 3 - xrange) "seems" a function, but it is a class, until quite simple to do the same. And the efficiency is so much greater than a list, the question that remains is "My God, how did you one day make the range of Python 2?? " :-)

In the very little used case in which you will call a function that really needs a list, you can convert a range object to a list by doing list(xrange(10)) .

How to create your: all an object of this needs is a way to (1) retrieve a number given an index, (2) need to interact the numbers starting at "start", and going to the "end" of "step by step" if used in a for, for example. (3) You also need to return your own length.

In Python, this means you have to have a class that implements (1) __getitem__, (2) __iter__, (3) __len__:

class MyRange(object):  # em Python 2 é obrigatório herdar de object
    def __init__(self, start, stop=None, step=1):
        if stop is None:
            stop = start
            start = 0
        self.start = start
        self.stop = stop
        self.step = step

    def __getitem__(self, index):
        return self.start + self.step * index

    def __len__(self):
        return (self.stop - self.start) // self.step

    def __iter__(self):
        v = self.start
        while (v < self.stop) if self.step > 0 else (v > self.stop):
            yield v
            v += self.step

This class is functionally the same. It does not treat some corner cases, but it also does not check whether any of the values is an integer: that is, it works for decimal numbers as well.