从While循环结构转换为函数调用

Question

我正在学习《Learn Python The Hard Way》这本书里的一个例子，但有些地方我想不明白。我觉得我在理解如何修改程序的理论部分上卡住了，而不是在写代码的具体行上，不过我也可能完全搞错了。

i = 0
numbers =[]
while i < 6:
    print "At the top i is %d" %i
    numbers.append(i)

    i += 1
    print "Numbers now: ", numbers
    print "At the bottom i is %d" %i

print "The numbers: "
for num in numbers:
    print num

这是我正在处理的代码，问题/提示是这样的：

把这个while循环转换成一个可以调用的函数，并把测试中的6（i < 6）替换成一个变量。

如果你能帮我，并且顺便把每一行的意义用简单的语言解释一下，那对我会非常有帮助。

这是我第一次尝试：

def whilefunc(i):
    numbers = []
    for i in range(0,6):
        print "At the top i is %d" %i
        numbers.append(i)
        i += 1
        print "Numbers now: ", numbers
        print "At the bottom, i is %d" %i
    for num in numbers: 
        print num

Answer 1

    def list_of_numbers(length):
       working_list = []
       for i in range(length):
          print "At the top i is %d" %i
          working_list.append(i)
          print "numbers now: ", working_list

       return working_list


    numbers = list_of_numbers(6)

    print "The numbers: "

    for num in numbers:
       print num

输出结果：

At the top i is 0
numbers now:  [0]
At the top i is 1
numbers now:  [0, 1]
At the top i is 2
numbers now:  [0, 1, 2]
At the top i is 3
numbers now:  [0, 1, 2, 3]
At the top i is 4
numbers now:  [0, 1, 2, 3, 4]
At the top i is 5
numbers now:  [0, 1, 2, 3, 4, 5]
The numbers: 
0
1
2
3
4
5

Answer 2

我觉得Zed Shaw只是想让我们把while循环（而不是for循环）转换成一个函数……所以我觉得这其实很简单。

def functiontocallforlist(x):
numList = []
i = 0
while i < x:
    print "At the top i is %d" % i
    numList.append(i)

    i += 1
    print "Numbers now: ", numList
    print "At the bottom i is %d" % i

#You can put whatever number you want as x really.
functiontocallforlist(8)

Answer 3

我来得有点晚，不过我也在上这门课，觉得可以参与讨论。我认为下面的代码正确地回答了这节课的学习练习中的1到3题。

    numbers = []
    def numbers_list(x,y):
        i = 0
        while i < x:
            print "At the top of i is %d" % i
            numbers.append(i)
            i += y
            print "Numbers now: ", numbers
            print "At the bottom of i is %d" % i
        return numbers

    numbers_list(6,1)
    print "the numbers: "

    for num in numbers:
        print num

输出结果和上面的一样。

Answer 4

上面黑鸟提的初始问题是来自Zed Shaw的《Learn Python the Hard Way》中的第33章的学习练习1。你可以在这里找到这个练习。

在第33章的学习练习1中，Shaw让你把练习中的示例循环改成一个函数，并把固定的循环条件换成一个变量。虽然上面的一些回答达到了这个目标，但没有一个完全按照Shaw的要求来做，Shaw的要求是只传递一个参数（上面最后一个回答很接近，但传递了两个参数）。下面有两个回答。第一个是最符合Shaw的学习练习1的答案，按照读者到目前为止学到的内容，只传递了一个参数。第二个则是让用户输入，而不是在函数调用中写死一个数字。

第一个答案：

def buildList(num):
    numList = []    
    i = 0       
    while i < num:
        numList.append(i)
        i += 1
        print "i: %d, " % i,
        print "list: ", numList
    #note: you don't need to return a value

#you can hard code any number here, of course
buildList(6)

这是第二个答案：

def buildList(num):
    #Convert num to int else infinite loop because num is a string
    num = int(num)  
    numList = []    
    i = 0       
    while i < num:
        numList.append(i)
        i += 1
        print "i: %d, " % i,
        print "list: ", numList

#getting/passing a string; converted to int within the function
answer = raw_input("Enter a number less than 10: ")
buildList(answer)

Answer 5

这个问题让你用函数调用来模仿一个while循环。你只需要让函数自己重复调用自己，也就是递归。

def f(i,x,numbers):
    if (i < x):
        print "At the top i is %d" %i
        numbers.append(i)

        i += 1
        print "Numbers now: ", numbers
        print "At the bottom i is %d" %i
        f(i,x,numbers)
    return numbers

numbers = f(0,6,[])
for num in numbers:
    print num

输出：

At the top i is 0
Numbers now:  [0]
At the bottom, i is 1
At the top i is 1
Numbers now:  [0, 1]
At the bottom, i is 2
At the top i is 2
Numbers now:  [0, 1, 2]
At the bottom, i is 3
At the top i is 3
Numbers now:  [0, 1, 2, 3]
At the bottom, i is 4
At the top i is 4
Numbers now:  [0, 1, 2, 3, 4]
At the bottom, i is 5
At the top i is 5
Numbers now:  [0, 1, 2, 3, 4, 5]
At the bottom, i is 6
0
1
2
3
4
5