Create a TSV (or CSV, depending on the extension) file listing the given 
    sequences.

    Arguments
    =========
    path: str or pathlib.Path
        The name of the file to create.  If the path extension is '.tsv', 
        fields will be delimited by tabs.  If the extension is '.csv', fields 
        will be delimited by commas.

    seqs: dict
        A mapping of names to sequences, which can be either protein or DNA.

def write_sequences_to_tsv(path, seqs):
    """
    Create a TSV (or CSV, depending on the extension) file listing the given 
    sequences.

    Arguments
    =========
    path: str or pathlib.Path
        The name of the file to create.  If the path extension is '.tsv', 
        fields will be delimited by tabs.  If the extension is '.csv', fields 
        will be delimited by commas.

    seqs: dict
        A mapping of names to sequences, which can be either protein or DNA.
    """
    import csv

    path = Path(path)
    delimiter = {'.tsv': '\t', '.csv': ','}[path.suffix]
    with path.open('w') as file:
        w = csv.writer(file, delimiter=delimiter)
        for row in seqs.items():
            w.writerow(row)