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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def parse_fasta(infile, upper=False):
    '''
    parse a fasta-formatted file and returns header
    can be a fasta file that contains multiple records.
    '''
    try:
        fp = must_open(infile)
    except:
        fp = infile
    # keep header
    fa_iter = (x[1] for x in groupby(fp, lambda row: row[0] == '>'))
    for header in fa_iter:
        header = next(header)
        if header[0] != '>':
            continue
        # drop '>'
        header = header.strip()[1:]
        # stitch the sequence lines together and make into upper case
        seq = "".join(s.strip() for s in next(fa_iter))
        if upper:
            seq = seq.upper()
        yield header, seq