Python 中xrange和range区别

先看看Python help()的说明

help(range)

Help on built-in function range in module __builtin__:

range(...)
    range(stop) -> list of integers
    range(start, stop[, step]) -> list of integers

    Return a list containing an arithmetic progression of integers.
    range(i, j) returns [i, i+1, i+2, ..., j-1]; start (!) defaults to 0.
    When step is given, it specifies the increment (or decrement).
    For example, range(4) returns [0, 1, 2, 3].  The end point is omitted!
    These are exactly the valid indices for a list of 4 elements.

help(xrange)

Help on class xrange in module __builtin__:

class xrange(object)
 |  xrange(stop) -> xrange object
 |  xrange(start, stop[, step]) -> xrange object
 |
 |  Like range(), but instead of returning a list, returns an object that
 |  generates the numbers in the range on demand.  For looping, this is
 |  slightly faster than range() and more memory efficient.
 |
 |  Methods defined here:
 |
 |  __getattribute__(...)
 |      x.__getattribute__('name') <==> x.name
 |
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]
 |
 |  __iter__(...)
 |      x.__iter__() <==> iter(x)
 |
 |  __len__(...)
 |      x.__len__() <==> len(x)
 |
 |  __reduce__(...)
 |
 |  __repr__(...)
 |      x.__repr__() <==> repr(x)
 |
 |  __reversed__(...)
 |      Returns a reverse iterator.
 |
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |
 |  __new__ = <built-in method __new__ of type object>
 |      T.__new__(S, ...) -> a new object with type S, a subtype of T

---

range
    函数说明：range([start,] stop[, step])，根据start与stop指定的范围以及step设定的步长，生成一个序列。

xrange
    函数说明：用法与range完全相同，所不同的是生成的不是一个数组，而是一个生成器。

for i in range(0, 100):
    print i
 
for i in xrange(0, 100):
    print i

打印结果相同，但range是生成list,xrange 每次调用返回其中的一个值。

---

a = range(0,100)
print type(a)
print a
print a[0], a[1]

打印结果：

<type 'list'>
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
0 1

.

a = xrange(0,100)
print type(a)
print a
print a[0], a[1]

打印结果：

<type 'xrange'>
xrange(100)
0 1

所以xrange做循环的性能比range好，尤其是返回很大的时候，尽量用xrange吧，除非你是要返回一个列表。