1010. Double Char

Given a string, you have to return a string in which each character (case-sensitive) is repeated once.

Examples (Input -> Output):

* "String"      -> "SSttrriinngg"
* "Hello World" -> "HHeelllloo  WWoorrlldd"
* "1234!_ "     -> "11223344!!__  "

Good Luck!

Solution:

def double_char(s: str) -> str:
    return "".join((lambda x: x+x)(i) for i in s)