Error in GFFParser: UnknownSeq is deprecated in biopython 1.81

[Kmassau]

from Bio.Seq import UnknownSeq is deprecated in biopython 1.81 ( https://github.com/biopython/biopython/blob/dcf52bd4546410e1a60d39fbcd4c0041ec1e6fe6/DEPRECATED.rst#biosequnknownseq) and we have the error below:

    from BCBio.GFF.GFFParser import GFFParser, DiscoGFFParser, GFFExaminer, parse, parse_simple
/usr/local/lib/python3.9/site-packages/BCBio/GFF/GFFParser.py:34: in <module>
    from Bio.Seq import UnknownSeq
E   ImportError: cannot import name 'UnknownSeq' from 'Bio.Seq' (/usr/local/lib/python3.9/site-packages/Bio/Seq.py)

I am reporting a problem with bcbio-gff-0.6.9, Biopython version 1.81.

[corneliusroemer]

Thanks! This came quite surprising, was there no deprecation warning added in Biopython 1.79? At least that would have allowed us to prepare :/

[abretaud]

no deprecation warning added in Biopython 1.79

I never saw one, but maybe the code is not using it enough to trigger the warning (just an import and isinstance check)

[StickHu]

So how can we correct the code to use?