>>> from Bio import SeqRecord
>>> writer = SeqRecord.io.make_writer(format = "fasta",
...                       outfile = open("sp.fasta", "w"))
>>> for record in SeqRecord.io.read("sprot38.dat"):
...     writer.write(record)
...
    .. a lot of output ...
>>>

    use Bio::SeqIO;
 
    $in  = Bio::SeqIO->new(-file => "sprot38.dat" ,
                           '-format' => 'swiss');
    $out = Bio::SeqIO->new(-file => ">sp.fasta" ,
                           '-format' => 'fasta');
 
    while ( my $seq = $in->next_seq() ) {
        $out->write_seq($seq);
    }