def label_residue(residue):
    """ Return a string of the label of the biopython [1] residue object.

    The label of the residue is the following:
        Chain + Position

    Parameters
    ----------
    residue: Bio.PDB.Residue.Residue
        The residue to be labeled.

    Notes
    -----
    1. http://biopython.org/wiki/Biopython

    """
    position = str(residue.id[1])
    chain = residue.parent.id
    return chain + position
