def checkDNA(DNA):
    if set(DNA.upper()).union({'A','C','G','T'}) != {'G','C', 'T', 'A'}:
        return 'Sorry!!! Wrong characters in your Sequence'
    else:
        return('CORRECT')
    
def percGC(DNA):
    ''' percGC calculates the percentage GC content in a DNA sequence 
    provided the sequence is made up of "G" "c" "A" or "T" '''
    if checkDNA(DNA) == 'CORRECT':
        a=DNA.count('G')
        b=DNA.count('C')
        c=((a+b)/len(DNA))*100
    return c

def perGC(DNA):
    ''' perGC calculates the percentage GC content in a DNA sequence'''
    a=DNA.count('G')
    b=DNA.count('C')
    c=((a+b)/len(DNA))*100
    return c