问题
I'm stuck at an exercise where I need to reverse a random string in a function using only a loop (for loop or while?).
I can not use ".join(reversed(string)) or string[::-1] methods here so it's a bit tricky.
My code looks something like this:
def reverse(text):
while len(text) > 0:
print text[(len(text)) - 1],
del(text[(len(text)) - 1]
I use the , to print out every single letter in text on the same line!
I get invalid syntax on del(text[(len(text)) - 1]
Any suggestions?
回答1:
The problem is that you can't use del on a string in python.
However this code works without del and will hopefully do the trick:
def reverse(text):
a = ""
for i in range(1, len(text) + 1):
a += text[len(text) - i]
return a
print(reverse("Hello World!")) # prints: !dlroW olleH
回答2:
Python string is not mutable, so you can not use the del statement to remove characters in place. However you can build up a new string while looping through the original one:
def reverse(text):
rev_text = ""
for char in text:
rev_text = char + rev_text
return rev_text
reverse("hello")
# 'olleh'
回答3:
Python strings are immutable. You cannot use del on string.
text = 'abcde'
length = len(text)
text_rev = ""
while length>0:
text_rev += text[length-1]
length = length-1
print text_rev
Hope this helps.
回答4:
Here is my attempt using a decorator and a for loop. Put everything in one file.
Implementation details:
def reverse(func):
def reverse_engine(items):
partial_items = []
for item in items:
partial_items = [item] + partial_items
return func(partial_items)
return reverse_engine
Usage:
Example 1:
@reverse
def echo_alphabets(word):
return ''.join(word)
echo_alphabets('hello')
# olleh
Example 2:
@reverse
def echo_words(words):
return words
echo_words([':)', '3.6.0', 'Python', 'Hello'])
# ['Hello', 'Python', '3.6.0', ':)']
Example 3:
@reverse
def reverse_and_square(numbers):
return list(
map(lambda number: number ** 2, numbers)
)
reverse_and_square(range(1, 6))
# [25, 16, 9, 4, 1]
来源：https://stackoverflow.com/questions/41322315/reversing-a-string-in-python-using-a-loop