Why is there empty quotation marks?

Question

Given a string, return a string where for every char in the original, there are two chars.

double_char('The') → 'TThhee'

double_char('AAbb') → 'AAAAbbbb'

double_char('Hi-There') → 'HHii--TThheerree'

Solution:

    def double_char(str):
      double_char = ""
      for i in range(len(str)):
        double_char += str[i]*2
      return double_char

Hello, I'm new here, and it's my first time discovering this website and adding a question, so I'm sorry if it's a bit unclear. Can someone please explain this one in detail ? Like why it has empty quotation marks?

Answer 1

def double_char(str):            # function double_char takes argument str
    double_char = ""             # create an empty string assign to variable double_char. In python you put "" or '' around text that you want as a string (text).
    for i in range(len(str)):    # iterate from 0 to length of string
        double_char += str[i]*2  # append character at position i from str and duplicate it
    return double_char           # return double_char