def write_top(outpath, molecules, title):
    """
    Write a basic TOP file.

    The topology is written in *outpath*. If *outpath* is en empty string, or
    anything for which ``bool(outpath) == False``, the topology is written on
    the standard error, and the header is omitted, and only what has been buit
    by Insane id displayed (e.g. Proteins are excluded).

    Parameters
    ----------
    outpath
        The path to the file to write. If empty, a simplify topology is
        written on stderr.
    molecules
        List of molecules with the number of them.
    title
        Title of the system.
    """
    topmolecules = []
    for i in molecules:
        if i[0].endswith('.o'):
            topmolecules.append(tuple([i[0][:-2]]+list(i[1:])))
        else:
            topmolecules.append(i)

    if outpath:
        # Write a rudimentary topology file
        with open(outpath, "w") as top:
            print('#include "martini.itp"\n', file=top)
            print('[ system ]', file=top)
            print('; name', file=top)
            print(title, file=top)
            print('\n', file=top)
            print('[ molecules ]', file=top)
            print('; name  number', file=top)
            print("\n".join("%-10s %7d"%i for i in topmolecules), file=top)
    else:
        # Here we only include molecules that have beed added by insane.
        # This is usually concatenated at the end of an existint top file.
        # As the existing file usually contain the proteins already, we do not
        # include them here.
        added_molecules = (molecule for molecule in topmolecules
                           if molecule[0] != 'Protein')
        print("\n".join("%-10s %7d"%i for i in added_molecules), file=sys.stderr)
Write a basic TOP file.

    The topology is written in *outpath*. If *outpath* is en empty string, or
    anything for which ``bool(outpath) == False``, the topology is written on
    the standard error, and the header is omitted, and only what has been buit
    by Insane id displayed (e.g. Proteins are excluded).

    Parameters
    ----------
    outpath
        The path to the file to write. If empty, a simplify topology is
        written on stderr.
    molecules
        List of molecules with the number of them.
    title
        Title of the system.