Reusable code for Codewars DNA code challenges

codewars_dna.py

# iterating a string and comparing it to dictionary values
# by adding the result variable, I eliminate redundant and costly printing, which is the PYTHONIC way to develop

d = {'A':'T','T':'A','C':'G','G':'C'}

for k in random_string:
    if k not in d:
       result = '{} is not valid. {} is the culprit!'.format(random_string,k)
       break    
       
    else:
       result = 'the string is alright.'
        
print(result)