def list_comp(the_list):
    return ''.join([item for item in the_list])

def gen(the_list):
    return ''.join(item for item in the_list)

a = list('abc' * 100000)

%timeit list_comp(a)
19.5 ms ± 106 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

%timeit gen(a)
33.3 ms ± 1.26 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)