In Python 2 is it more performative to use range or xrange?

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The programming language I use the most is PHP :( and, after it has been implemented Generators in version 5.5, it is said to be faster to use it for generating numbers in sequence than with the function range - which creates a array with the sequence, unlike the Generator, that could generate a number at a time by yield.

Example range PHP:

range(1, 1000); // Retorna: [1, 2, 3, ..., 1000]

Example Generator PHP:

function xrange($start, $limit, $step = 1) {
    if ($start < $limit) {
        if ($step <= 0) {
            throw new LogicException('Step must be +ve');
        }

        for ($i = $start; $i <= $limit; $i += $step) {
            yield $i;
        }
    } else {
        if ($step >= 0) {
            throw new LogicException('Step must be -ve');
        }

        for ($i = $start; $i >= $limit; $i += $step) {
            yield $i;
        }
    }
}

The exit would be:

xrange(); // Generator(object)

According to the staff of PHP, in a numerical sequence generation with range in PHP with 1000000 would use more than 100MB of memory, while with a Iterator who would do the same thing, spend 1kb in memory.

Python

Based on this, I realized that in Python the sequences generated by range are lists, different from the version 3, that returns an object Range.

Also in Python there is a function called xrange (which is imitated by PHP in this page), that returns a Generator.

The point is: The fact of range in Python returning a list would not make this function more expensive, as for memory, because of the list that is generated?

If I want to make one range of 1 to 1000, in Python, it would be more advisable to use xrange, or the very range would not harm the memory consumption?

python
  • 2

    -1 by comparing python to php :P. The question is about python and has the php tag all right? -1 was a joke, +1

  • 1

    @rray is the "language addiction". Did anyone notice the pun? Well, the intention was to put Python even, value ;)

  • About php: Looking at some examples, not in all cases was faster, there were cases that were the opposite, but in memory consumption it was the great advantage for php. A range(0, 1000000) can result in more than 100mb of memory consumption or.0 ... Already with Generator will be a few kb.

  • I think recent versions of Python already implement range() as xrange() and the performance difference no longer exists.

1 answer

6

As you raised, the function range(x, y) creates a list of x to y.

The function xrange(x,y) generates each element individually, and this saves memory and time startup.

Recalling that in the case of 1000 elements, the drop in performance would be almost imperceptible. But in larger proportions could rather lead to a decrease in computer performance by excessive memory consumption.

The performance of range() is worse, and the reason is simple, when you use for example the function so:

for x in range(0, 1000000000):
    print x

The function creates a list of 1 billion elements and allocate it in memory.

While with the function xrange():

for x in xrange(0,1000000000):
    print x

The function generates the elements one time saving memory and running time.

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