Learn Python The Hard Way学习(32)
下面我们会做一些有趣的事情，如果跟着进度学习的话，你会发现你已经可以用if语句和布尔表达式做很多事情了。不管怎样，程序会做一些重复的事情，下面我们就用for循环打印一个列表变量。做这个练习的时候你必须自己弄懂它们的含义和作用。
在使用for循环之前，我们需要一个东西保存循环的值，最好的方法是使用一个列表，列表就是按照顺序保存数据的容器，不是很复杂，就是一种新的语法而已，结构像下面这样：
hairs = ['brown', 'blond', 'red']
eyes = ['brown', 'blue', 'green']
weights =
list以 [ 号开头，里面的元素以 , 号分隔，像函数的参数一样，然后以 ] 结束，python把所有这些包含在一个变量中。
敬告：上一个练习中我们用if语句包含if语句，很多人不明白为什么一个东西可以包含另外一个东西，在程序中这是很常见的，你会发现函数可以包含函数，list可以包含list。如果你发现一种不理解的结构，用笔记录下来，以后弄明白它。
下面我们来看一些list，并且循环打印它们：
the_count =
fruits = ['apples', 'oranges', 'pears', 'apricots']
change =
# 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 on
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 "Elements was: %d" % i
运行结果
root@he-desktop:~/mystuff# python ex32.py
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 'domes'
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.
Elements was: 0
Elements was: 1
Elements was: 2
Elements was: 3
Elements was: 4
Elements was: 5
加分练习
1. 弄懂range函数。
range(, stop[, step])
产生一个整数列表，step默认是1，如果start没有赋值，默认是从0开始。
2. 你能不能不使用22行的for循环，而直接使用range给elemens赋值呢？
elements = range(0, 6)
3. 查看list的帮助文档，看看append附近还有什么函数。
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