In [75]: from Bio.Seq import Seq
    ...:
    ...: def my_reverse_complement(seq):
    ...:     return Seq(seq).reverse_complement()
    ...:

In [76]: import string
    ...: tab = str.maketrans("ACTG", "TGAC")
    ...:
    ...: def reverse_complement_table(seq):
    ...:     return seq.translate(tab)[::-1]
    ...:

In [77]: s = 'ATGCGTA'* 100000

In [78]: %timeit my_reverse_complement(s)
100 loops, best of 3: 1.63 ms per loop

In [79]: %timeit reverse_complement_table(s)
1000 loops, best of 3: 1.33 ms per loop

In [80]: %timeit my_reverse_complement(s)
1000 loops, best of 3: 1.54 ms per loop

In [81]: %timeit reverse_complement_table(s)
1000 loops, best of 3: 1.29 ms per loop