程序从不进入第二个 elif 语句，我不知道为什么

Question

I am currently doing an assignment to analyze a string of letters , and print out the longest alphabetically ordered part of it. This is the code I wrote for it, but the only output I receive is 'az' instead of the expected output: 'beggh'. After adding some print statements I saw that the second elif statement only goes through on the loops first iteration, and then it is basically stuck in the first elif, permanently increasing end_string without ever comparing it to max_end_string again.

s = 'azcbbobobegghakl'
end_string = ''
max_end_string = ''
for char_counter in range(len(s)):
    if char_counter >= len(s)-1:
        break
    elif (s[char_counter] < s[char_counter + 1]) or (s[char_counter] > s[char_counter - 1]):
        end_string = end_string + s[char_counter]
    elif len(end_string) > len(max_end_string):
        max_end_string = end_string
        end_string = ''
print(max_end_string)

Answer 1

I have fixed your code. Have a good day.

s = 'azcbbobobegghakl'
end_string = ''
max_end_string = ''
for char_counter in range(len(s)):

    #skip check for char_counter == 0 since the first character is always alphabetical
    #check if the current character is >= to previous alphabetically
    if char_counter == 0 or s[char_counter] >= s[char_counter - 1]:
        end_string += s[char_counter] #add current character to current string
    else:
        #check if the current string is the longest
        if len(end_string) > len(max_end_string):
            max_end_string = end_string

        #add the current character to the next temp string
        #Note: it is necessary to do this rather than simply clearing end_string
        #(Consider the following case: "azabc")
        end_string = s[char_counter]

#final check in case the longest string contains the last character
#(Consider the following case: "azabc")
if len(end_string) > len(max_end_string):
    max_end_string = end_string

print(max_end_string)

Answer 2

Here's another potential solution, which to my eyes seems cleaner -- you be the judge.

First thing I want to mention though is that it's not necessary to add a conditional to check that the index of the current character is less than the length of the string.

for char_counter in range(len(s)):
    if char_counter >= len(s)-1:

instead just subtract 1 from the range for char_counter in range(len(s) - 1):

And here's the solution I came up with (changed the variable names to something easier for me to read):

letters = "azcbbobobegghakl"
longest = ""
temp = letters[0]

def alphabetical(letter, next_letter):
    # This statement could be worked into your loop
    # broken out into its own function for readability
    if letter <= next_letter:
        return True
    else:
        return False

for i in range(len(letters) - 1):
    if alphabetical(letters[i], letters[i + 1]):
        # if the current letter is less than the next, concatenate the next to our temporary string
        temp += letters[i + 1]
    elif len(temp) > len(longest):
        # if the current letter is greater than the next letter check if
        # our temporary string is longer than our longest string
        # if so, that's our new longest.
        # start the temp string over with the next letter
        longest = temp
        temp = letters[i + 1]
    else:
        # if the temp string is shorter than the longest then
        # redeclare the temporary string with the next letter
        temp = letters[i + 1]

print(longest)