Class FingerprintFromFileGenerator

Class to generate (identifier, fingerprint) items, one at a time,
from a structure file.  Optional property filtering controls which
structures are emitted as fingerprints.  By default only unique
structures, as judged by C{id_prop}, are generated.

API Examples:
-------------

# Only unique fingerprint for structures with a title of 'foo',
# 'bar', or 'baz' are generated.
activefps = FingerprintFromFileGenerator(
    structure.StructureReader('mystructures.mae'),
    fp_gen,
    prop_filter={'s_m_title': ['foo', 'bar', 'baz']}, 
)
for id, fp in activefps:
    process_fingerprint(fp)

# Only unique fingerprint for structures that don't have a title
# of 'foo', 'bar', or 'baz' are generated.
inactivefps = FingerprintFromFileGenerator(
    structure.StructureReader('mystructures.mae'),
    fp_gen,
    prop_filter={'s_m_title': ['foo', 'bar', 'baz']}, 
)
inactivfps.setInvertFilter()
for id, fp in inactivefps:
    process_fingerprint(fp)