Computing GC Content

file = open('rosalind_gc.txt', "r")
name = None
seqs = dict()
s = ''

def readFASTA(file): # this function create a dictionary with the fasta file
    name = None
    seqs = dict()
    for line in file:
        # let's discard the newline at the end (if any)
        line = line.rstrip()
        # distinguish header from sequence
        if line[0] == '>':  # or line.startswith('>')
            # it is the header
            name = line[1:]  # discarding the initial >
            seqs[name] = ''
        else:
            # it is sequence
            seqs[name] = seqs[name] + line
    return seqs

def GCcontent(dict): # here it counts the occurence of a GC and returns the GC content %
    cache = [0,0]
    for i in dict:
        nucleotide = "GC"
        GC = round(((dict[i].count("C") + dict[i].count("G"))/len(dict[i])*100),6)
        if GC > cache[1]:
            cache = [i, GC]
    print(cache[0]) # printitng the reuslt as rosalind want
    print(cache[1])
    return

print(GCcontent(readFASTA(file)))