def complement(dna):
    dna2= ""
    for letter in dna:
        if(letter == 'A'):
            dna2 += 'T'
        elif(letter == 'C'):
            dna2 += 'G'
        elif(letter == 'T'):
            dna2 += 'A'
        elif(letter == 'G'):
            dna2 += 'C'
    return dna2

def reverse_complement(dna):
    dna2 = complement(dna)
    x = dna2[::-1]
    return x

sites = []

def restriction_sites(dna):
    
    dna3 = reverse_complement(dna)
    for i in range(4,12,2):
        for x in dna3:
            if(dna[x:x+1] == dna3[x:x+1]):
                sites.append((dna[x+1], dna[x+i], dna[x:x+i]))

dna = 'TCAATGCATGCGGGTCTATATGCAT'

print(dna)
print(complement(dna))
print(reverse_complement(dna))
print(restriction_sites(dna))