Question

我正在尝试编写一个递归程序，它返回一个非元音单词的字母串。我的代码现在打印出“大学”的所有非元音，但永远不会结束。有什么想法吗？

def removeVowels9(aString):
    if len(aString) == 0:
        return newString
    else:
        newString = aString[1:len(aString) + 1]
        firstLetter = aString[0]
        #print(firstLetter)
        if firstLetter in "aeiouAEIOU":

            return removeVowels9(newString)
        else:
            newString = newString + firstLetter
            print(newString)

            return removeVowels9(newString)

Answer 1

显然，你永远不会遇到基本情况，因为你会得到一个NameError（newString尚未定义）。

为什么呢？让我们来看看你的第三个案例：

else: # starts with consonant
    newString = newString + firstLetter # add first letter to the end?
    return removeVowels9(newString) # repeat

一旦你删除了所有元音，这就会继续循环辅音，正如你应该从输出中看到的那样：

>>> removeVowels9("University")
iversityn
ersitynv
sitynvr
itynvrs
ynvrst # all vowels gone
nvrsty
vrstyn
rstynv
stynvr
tynvrs
ynvrst # just keeps looping
...

这是最小的修复：

>>> def removeVowels9(aString):
    if len(aString) == 0:
        return aString # aString, not newString
    else:
        newString = aString[1:len(aString) + 1]
        firstLetter = aString[0]
        #print(firstLetter)
        if firstLetter in "aeiouAEIOU":

            return removeVowels9(newString)
        else:
            return firstLetter + removeVowels9(newString) # add first letter back at start, after processing rest


>>> removeVowels9("University")
'nvrsty'

但这可能更整洁：

def remove_vowels(s):
    """Recursively remove vowels from the input."""
    if not s: # empty string
        return s
    elif s[0] in "aeiouAEIOU": # first character is vowel
        return remove_vowels(s[1:]) # skip first character and process rest
    return s[0] + remove_vowels(s[1:]) # return first character and process rest

其中：

>>> remove_vowels("University")
'nvrsty'

请注意与变量名等的the style guide的兼容性。

删除元音的递归函数

1 个答案: