‘str’ object does not support item assignment

I would like to read some characters from a string s1 and put it into another string s2.

However, assigning to s2[j] gives an error:

s2[j] = s1[i]

# TypeError: 'str' object does not support item assignment

In C, this works:

int i = j = 0;
while (s1[i] != '\0')
    s2[j++] = s1[i++];

My attempt in Python:

s1 = "Hello World"
s2 = ""
j = 0

for i in range(len(s1)):
    s2[j] = s1[i]
    j = j + 1