python – How do I convert this iterative function to a recursive one?

This function map input strings to that in a dictionary, outputting the result. Any idea how this can be approached recursively?

def dna(seq):
    hashy = {'A': 'U', 'G': 'C', 'T': 'A', 'C': 'G'}
    ans = ''
    for i in range(len(seq)):
        ans += hashy(seq(i))
    return ans


print(dna('AGCTGACGTA'))

Thanks.