def __init__(self, proper_hits_diamond, decoy_diamond=None):
self._decoy_diamond = decoy_diamond<EOL>self._proper_hits_diamond = proper_hits_diamond<EOL>
Create a new DecoyFilter.

        Parameters
        ----------
        proper_hits_diamond: Diamond
            Diamond object containing real sequences.
        decoy_diamond: Diamond or None.
            Diamond object with db containing decoy sequences. If None, no
            searching against a decoy database is carried out.