Rewrites a specific sequence in a multifasta file while keeping the sequence header.

    :param sequence: a string with the sequence to be written
    :param sequence_name: the name of the sequence to be retrieved eg. for '>2 dna:chromosome chromosome:GRCm38:2:1:182113224:1 REF' use: sequence_name=str(2)
    :param fasta_in: /path/to/original.fa
    :param fasta_out: /path/to/destination.fa

    :returns: nothing

def rewriteFasta(sequence, sequence_name, fasta_in, fasta_out):
    """
    Rewrites a specific sequence in a multifasta file while keeping the sequence header.

    :param sequence: a string with the sequence to be written
    :param sequence_name: the name of the sequence to be retrieved eg. for '>2 dna:chromosome chromosome:GRCm38:2:1:182113224:1 REF' use: sequence_name=str(2)
    :param fasta_in: /path/to/original.fa
    :param fasta_out: /path/to/destination.fa

    :returns: nothing
    """
    f=open(fasta_in, 'r+')
    f2=open(fasta_out,'w')
    lines = f.readlines()
    i=0
    while i < len(lines):
        line = lines[i]
        if line[0] == ">":
            f2.write(line)
            fChr=line.split(" ")[0]
            fChr=fChr[1:]
            if fChr == sequence_name:
                code=['N','A','C','T','G']
                firstbase=lines[i+1][0]
                while firstbase in code:
                    i=i+1
                    firstbase=lines[i][0]
                s=0
                while s <= len(sequence):
                    f2.write(sequence[s:s+60]+"\n")
                    s=s+60
            else:
                i=i+1
        else:
            f2.write(line)
            i=i+1

    f2.close
    f.close