a = '123456789'
print(a[::-1])

print(''.join(reversed('123456789')))

def reversed_string(a_string):
    return a_string[::-1]
print(reversed_string('123456789'))

# 下標通過在大括號中包含冒號來創(chuàng)建切片：
string[start:stop:step]
# 要在大括號外創(chuàng)建切片，您需要創(chuàng)建切片對
slice_obj = slice(start, stop, step)
string[slice_obj]

def reverse_a_string_slowly(a_string):
? ? new_string = ''
? ? index = len(a_string)
? ? while index:
? ? ? ? index -= 1 ? ? ? ? ? ? ? ? ? ?# index = index - 1
? ? ? ? new_string += a_string[index] # new_string = new_string + character

def reverse_a_string_more_slowly(a_string):
    new_strings = []
    index = len(a_string)
    while index:
        index -= 1                       
        new_strings.append(a_string[index])
    return ''.join(new_strings)

def string_reverse(a_string):
    n = len(a_string)
    x=""
    for i in range(n-1,-1,-1):
        x += test[i]
    return x

reduce(lambda x,y : y+x, a_string)

def rev_string(s): 
    if len(s) == 1:
        return s
    return s[-1] + rev_string(s[:-1])

a_string='123456789'
def rev_string(a_string):
    l=list(a)
    l.reverse()
    return ''.join(l)

def rev_string(a_string):
    l = list(a_string) #模擬全部入棧
    new_string = ""
    while len(l)>0:
        new_string += l.pop() #模擬出棧
    return new_string