Hi all, I have a genome of size 7190 mb. I am using following python code to extract the flanking sequence nucleotide sequence around a list of variants. My code works for a smaller genome but it takes so long to process and fetch the sequence from a fasta file. Is there any way to speed up the process?

here is my code:

fr = open("cov_40/rep_1/test.vcf", "r")
a = fr.read()
aa = a.split("#CHROM")
aaa = aa[1].split("\n")

seq = ''
header = ''
sequence = {}
new_dict = {}


with open("Agria_reference_sequence_final.fasta") as fs:
    for linee in fs:
        if linee.startswith(">"):
            header = linee.split("\n")[0]
            seq = ''
            # print(header)

        else:
            seq = seq + linee.split("\n")[0]
            sequence.update({header: seq})
            # print(seq)

for line in aaa[1:-1]:
    index1 = line.split('\t')[0]
    index = line.split()
    # print(index[0],index[1],index[2],index[3],index[4] )
    head = index[0] + " " + index[1] + " " + index[2] + " " + index[3] + " " + index[4] + " " + " " + index[5]
    for keys, values in sequence.items():
        if index1 in keys:
            site = int(index[1]) - 1

            start = abs(site - 10)
            end = site + 50
            seqq = values[start:end + 1]
            new_dict.update({head: seqq})

fw = open("per_variants.txt", "a")
for base, basee in new_dict.items():
    fw.write(str(base) + " " + str(basee) + "\n"