python3，如何反转句子中单词的每个字母

Question

s="I love you"

how can I get "I evol uoy" ?

I tried...

words=s.split()

for x in words:
    c=list(x)
    c.reverse()
    " ".join(c)

and I get...

'I'
'evol'
'uoy'

I again tried...

words=s.split()
s1=[]

for x in words:
   c=list(x)
   c.reverse()
   for y in c:
       s1.append(y)

Now s1 is:

['I', 'e', 'v', 'o', 'l', 'u', 'o', 'y']

but there is no space between words.

Answer 1

Use split to get the words then loop over and reverse each word and then join them.

>>> s = "I love you"
>>> " ".join(word[::-1] for word in s.split())
'I evol uoy'

Answer 2

Here's how to fix your first solution:

s = "I love you"

words = s.split()

def reverse_word(x):
    c = list(x)
    c.reverse()
    return "".join(c)

result = " ".join(reverse_word(w) for w in words)

print(result)

The important things to fix are that:

1. Simply calling " ".join(c) without making use of it somewhere doesn't help. c is a copy of x , and reversing it doesn't change x .
2. " ".join(c) is wrong anyway because you don't want a space between letters, so it's now "".join(c) . The spaces are added to the actual reversed sentence.

And the second one:

s1 = []

for x in words:
    new_word = []
    c = list(x)
    c.reverse()
    for y in c:
        new_word.append(y)
    s1.append("".join(new_word))

result = " ".join(s1)

The important difference here is that you need a list for each word (consisting of letters) as well as for the whole sentence (consisting of words), since as you saw a single list for both doesn't work. I've kept it similar to your code but the new_word is actually redundant since it's just an exact copy of c . So it could be simplified as follows:

s1 = []

for x in words:
    c = list(x)
    c.reverse()
    s1.append("".join(c))

result = " ".join(s1)

This is an extremely common pattern: create an empty list, append some element to it in each iteration of a for loop, and then keep the final result. It's so common that Python has a special syntax for it called list comprehensions:

def reverse_word(x):
    c = list(x)
    c.reverse()
    return "".join(c)

s1 = [reverse_word(word) for word in words]

This is the more elegant, Pythonic way. In fact you'll notice now that the first bit of code above is almost exactly this, except that I immediately used s1 without even naming it, and there are no square brackets because now it's a generator comprehension and a nice little feature of Python's syntax means that just the parentheses are valid since join only takes a single argument. But now we're getting deep, don't worry too much.

Finally reverse_word(word) can simply be replaced by word[s::-1] using Python's slice notation, and everything can be done in one step, and that's the solution given by AKS.

Answer 3

将字符串拆分为单词，反转每个单词，然后将其加入。

' '.join(i[::-1] for i in s.split())