交替添加大写和小写字母？

Question

I am working on a task for a beginner python course. Task is to take first uppercase letter and then lowercase letter and all over again.

this is input string:

"ifeFemFEkej83FkW"

and this should be output string:

FeFkFkW

friend and I came up with this solution, but it looks a little bit complicated, and I was wondering if there is maybe one-line solution or regular expression for some part of the code? Or maybe some different approach to the task. Thank you for your help.

str_a = "ifeFemFEkej83FkW"
new = ""
upper_case = True

for i in str_a:
    if "A" < i < "Z" and upper_case == True:
        new += i
        upper_case = False
    elif "a" < i < "z" and upper_case == False:
        new += i
        upper_case = True

print(new)

Answer 1

Here's a way to simplify it, using the isupper() function and the fact that you can always flip a bool to its opposite with not :

str_a = "ifeFemFEkej83FkW"
new = ""
upper_case = True

for i in str_a:
    if i.isupper() == upper_case:
        new += i
        upper_case = not upper_case

print(new)

And here's an approach with itertools.groupby . This would be a pretty clean one-liner if not for the requirement of dropping initial lowercase letters:

import itertools

str_a = "ifeFemFEkej83FkW"

new = ''.join(next(g) for _, g in itertools.groupby(str_a, str.isupper))
new = new if new[0].isupper() else new[1:]

print(new)