Write a function called double_str that takes a string argument and returns a new string that has all of the same characters as the argument, except each one is repeated twice. For example:

double_str('dog') --> 'ddoogg'

looking for python coding below is what I have so far

double_str = 'robert'

double_str 'robert'

for i in range(len(double_str)):

print(double_str[i])