The use of xrange and yield in Python

Believe that many people on xrange and yield are not very clear, many articles on the web is also written foggy, today I use the simplest example to everyone said.

Talk about xrange When you must mention range, in fact xrange usage and range exactly the same, the difference is not a list object is generated, but a generator.

>>> xrange (5) xrange (5)>>> list (xrange (51, 2, 3, 4) >> > xrange (1,5) xrange (1, 5)>>> list (xrange (1,5)) [1, 2, 3, 4]>> > xrange (0,6,26, 2)>>> list (xrange (0,6,22, 4)

As can be known from the above example: in order to generate a large number sequence, using xrange will be much better than range performance, because there is no need to open up a large amount of memory space.

Both the xrange and range are basically used in the loop.

For I in range (0, 100):
Print I

For I in xrange (0, 100):
Print I
The results of both outputs are the same, in fact there are many differences, and range generates a list object directly:

A = range (0,100)

Print type (a)

Print a

Print A[6]

<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 3, 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]

5

b = xrange (0,100)

Print type (b)

Print B

Print B[6]

<type ' xrange ' >

Xrange (100)

5

Summary: By using the above example, we can tell that the difference between Python's xrange and range is that xrange generates not an array, but a generator.

Yield is the same truth, see Example 1

def spam ():

Yield 1

Yield 2

Yield 3

Print spam

<function spam at 0x1006f5488>

For item in spam ():

Print Item

1

2

3

or through next () access

Gen = spam ()

Gen.next ()

Gen.next ()

Gen.next ()

1

2

3

Example 2

defAlexreadline (): Seek=0 whileTrue:with Open ("Temp.txt"," R ") as F:f.seek (seek) data=F.readline ()ifData:seek=F.tell ()yieldDataElse:                     returnPrintAlexreadline ()
<generator Object Alexreadline at 0x1006f5488>
For item in Alexreadline ()
Print Item

Hello
World

Description: The data will be printed only when it is accessed

Using a small instance of my work to describe the use of these two generators together:

# encoding=utf=8 def foo (l,n):      for inch xrange (0,len (L), N):         yield l[x:x+= range (all) for in foo (mm,3):     Print AA

[0, 1, 2]

[3, 4, 5]

[6, 7, 8]

[9, 10, 11]

[12, 13, 14]

[15, 16, 17]

[18, 19, 20]

The use of xrange and yield in Python