a = "qwertyuiop"

def t1(t):
    a_ = a
    for _ in range(t):
        x = a_

def t2(t):
    for _ in range(t):
        x = a

%timeit t1(10000000)
1 loops, best of 3: 551 ms per loop

%timeit t2(10000000)
1 loops, best of 3: 712 ms per loop