how to include variable in variable string code example

Example 1: insert into string python

def insert (source_str, insert_str, pos):
    return source_str[:pos]+insert_str+source_str[pos:]

Example 2: embed variables python

#Pre 3.6
print('Hi, my name is {name} and my age is {age}'.format(**locals()))

#After 3.6
print('Hi, my name is {name} and my age is {age}')