为什么此代码不向后打印字符

Question

def anti_vowel(text):
    p=''
    for c in text:
        if c=='a' or c=='A':
            break
        elif c=='e' or c=='E':
            break
        elif c=='i' or c=='I':
            break
        elif c=='o' or c=='O':
            break

        elif c=='u' or c=='U':
            break
        else:
            p=p+c



print(anti_vowel('Hello you'))

Answer 1

You forgot to return p at the end of your function:

def anti_vowel(text):
    p=''
    for c in text:
        if c=='a' or c=='A':
            break
        elif c=='e' or c=='E':
            break
        elif c=='i' or c=='I':
            break
        elif c=='o' or c=='O':
            break
        elif c=='u' or c=='U':
            break
        else:
            p=p+c
    return p

Without that last line all you'll ever print is None , the default return value for functions without an explicit return statement.

Of course, your function will only ever print the first consonants, as break ends the loop as soon as you find any vowels. It'll not reverse the string, ever. For your sample input, the function return 'H' , because the next letter in the input is a vowel, and break then ends the loop.

You could easily re-write your function to use str.lower() and a containment test:

def anti_vowel(text):
    p = ''
    for c in text:
        if c.lower() in 'aeiou':
            break
        p += c
    return p

This does the same thing, return the first consonants ( 'H' for your sample input).

If you wanted to reverse letters, and exclude vowels, don't use break and invert where you place the remaining letters. You could use continue instead, or more simply, just invert the if test and only process a chararter if it is not a vowel:

def anti_vowel(text):
    p = ''
    for c in text:
        if c.lower() not in 'aeiou':
            p = c + p
    return p

Now consonants are placed before any preceding consonants, reversing the text:

>>> def anti_vowel(text):
...     p = ''
...     for c in text:
...         if c.lower() not in 'aeiou':
...             p = c + p
...     return p
... 
>>> anti_vowel('Hello you')
'y llH'