python 中的字符串字符之间的不等式

Question

I am new to StackOverflow so forgive me if I did any formatting wrong.

I am trying to extract the largest substring (with variable name 'longest_string') which follows an alphabetical order (ie a,b,x,y,z is valid, but a,c,b is not) from a string (with variable name 's').

What I tried to do is to create a loop which looped over every single character in ' s ', and assigned the first character of string s to the variable ' current_value ' and add it into a list called ' strings '. Then, I compare the subsequent character to see if that character is larger than or equal to the current_value . If it is, then I add it to ' strings ', and if it isn't, I assigned the initial ' strings ' list to the ' longest_string ' list and refreshed the variable ' current_value ' and ' strings '. Each time the subsequent character is smaller than the ' current_value ', the length of current ' strings ' is compared with the ' longest_string ' and the longest one is assigned as ' longest_string '.

What I understand is that Python assumes that the first alphabet in the 26 English character to be the smallest (ie 'a' > 'z' will return False). However, when I run the below code:

s = 'zcbobobegghakl'
longest_string = None
current_value = None
strings = []

for i in s:
    if not current_value:
        current_value = i
        strings.append(i)
        continue

    if i >= current_value:
        strings.append(i)

    if i < current_value:
        if not longest_string or len(longest_string) < len(strings):
            longest_string = strings
        current_value = i
        strings = []
        
print(longest_string)

I get this output instead:

['o', 'b', 'o', 'b', 'e', 'g', 'g', 'h']

Why is it that the character 'b' got assigned into the same string as 'o' when clearly 'b' > 'o' will return False and thus make the 2nd IF statement False, wouldn't it not execute the 2nd IF statement in the first place?

Answer 1

Try adding this into the beginnig of the loop. Maybe this will give you some insight?

...
for i in s:
    print(i, current_value, strings)
    if not current_value:
...

Why is it that the character 'b' got assigned into the same string as 'o'

current_value only decreases, and after you encounter first b accumulation continues until a is found