Python How to capitalize nth letter of a string

Capitalize n-th character and lowercase the rest as capitalize() does:

def capitalize_nth(s, n):
    return s[:n].lower() + s[n:].capitalize()

my_string[:n] + my_string[n].upper() + my_string[n + 1:]

Or a more efficient version that isn't a Schlemiel the Painter's algorithm:

''.join([my_string[:n], my_string[n].upper(), my_string[n + 1:]])