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一入python深似海--range()与for

2024-07-07 06:30:01   228人阅读

range用法

使用python的人都知道range()函数很方便，今天再用到他的时候发现了很多以前看到过但是忘记的细节。

这里记录一下：

range(1,5)#代表从1到5(不包含5)
[1,2,3,4]
range(1,5,2)#代表从1到5，间隔2(不包含5)
[1,3]
range(5)#代表从0到5(不包含5)
[0,1,2,3,4]

再看看list的操作:

array= [1,2,5,3,6,8,4]
#其实这里的顺序标识是
[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


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