一入python深似海--range()、list与for

range使用方法

使用python的人都知道range()函数非常方便，今天再用到他的时候发现了非常多曾经看到过可是忘记的细节。

这里记录一下：

range ( 1 , 5 ) #代表从1到5(不包括5)

[ 1 , 2 , 3 , 4 ]

range ( 1 , 5 , 2 ) #代表从1到5，间隔2(不包括5)

[ 1 , 3 ]

range ( 5 ) #代表从0到5(不包括5)

[ 0 , 1 , 2 , 3 , 4 ]

再看看list的操作:

array =  [ 1 , 2 , 5 , 3 , 6 , 8 , 4 ]

#事实上这里的顺序标识是

[ 1 , 2 , 5 , 3 , 6 , 8 , 4 ]

( 0 。 1 ， 2 。 3 ， 4 ， 5 ， 6 )

( - 7 , - 6 , - 5 , - 4 , - 3 , - 2 , - 1 )

 

array[ 0 :] #列出0以后的

[ 1 , 2 , 5 , 3 , 6 , 8 , 4 ]

array[ 1 :] #列出1以后的

[ 2 , 5 , 3 , 6 , 8 , 4 ]

array[: - 1 ] #列出-1之前的

[ 1 , 2 , 5 , 3 , 6 , 8 ]

array[ 3 : - 3 ] #列出3到-3之间的

[ 3 ]

for loop

the_count = [1, 2, 3, 4, 5]
fruits = ['apples', 'oranges', 'pears', 'apricots']
change = [1, 'pennies', 2, 'dimes', 3, 'quarters']

# this first kind of for-loop goes through a list
for number in the_count:
    print "This is count %d" % number

# same as above
for fruit in fruits:
    print "A fruit of type: %s" % fruit

# also we can go through mixed lists too
# notice we have to use %r since we don't know what's in it
for i in change:
    print "I got %r" % i

# we can also build lists, first start with an empty one
elements = []

# then use the range function to do 0 to 5 counts
for i in range(0, 6):
    print "Adding %d to the list." % i
    # append is a function that lists understand
    elements.append(i)

# now we can print them out too
for i in elements:
    print "Element was: %d" % i

输出

This is count 1
This is count 2
This is count 3
This is count 4
This is count 5
A fruit of type: apples
A fruit of type: oranges
A fruit of type: pears
A fruit of type: apricots
I got 1
I got 'pennies'
I got 2
I got 'dimes'
I got 3
I got 'quarters'
Adding 0 to the list.
Adding 1 to the list.
Adding 2 to the list.
Adding 3 to the list.
Adding 4 to the list.
Adding 5 to the list.
Element was: 0
Element was: 1
Element was: 2
Element was: 3
Element was: 4
Element was: 5