# FRUIT_NAMES was a list-module imported on the website -- not available to view

# Deoxyribonucleic acid (DNA) is a chemical found in the nucleus of cells and carries the "instructions" 
# for the development and functioning of living organisms.

# If you want to know more http://en.wikipedia.org/wiki/DNA

# In DNA strings, symbols "A" and "T" are complements of each other, as "C" and "G". You have function 
# with one side of the DNA (string, except for Haskell); 
# you need to get the other complementary side. DNA strand is never empty 
# or there is no DNA at all (again, except for Haskell).


# DNAStrand ("ATTGC") // return "TAACG"

# DNAStrand ("GTAT") // return "CATA" 

def DNA_strand(dna):
    return "".join([{"A": "T", "T": "A", "C":"G", "G":"C"}[letter] for letter in dna])



# https://www.codewars.com/kata/554e4a2f232cdd87d9000038/train/python