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== Writing GFF3 ==
== Writing GFF3 ==
Revision as of 23:42, 12 July 2009
Note: GFF parsing is not yet integrated into Biopython. This documentation is work towards making it ready for inclusion. You can retrieve the current version of the GFF parser from: http://github.com/chapmanb/bcbb/tree/master/gff. Comments are very welcome.
Generic Feature Format (GFF) is a biological sequence file format for representing features and annotations on sequences. It is a tab delimited format, making it accessible to biologists and editable in text editors and spreadsheet programs. It is also well defined and can be parsed via automated programs. GFF files are available from many of the large sequencing and annotation centers. The specification provides full details on the format and its uses.
Biopython provides a full featured GFF parser which will handle several versions of GFF: GFF3, GFF2, and GTF. It supports writing GFF3, the latest version.
GFF parsing differs from parsing other file formats like GenBank or PDB in that it is not record oriented. In a GenBank file, sequences are broken into discrete parts which can be parsed as a whole. In contrast, GFF is a line oriented format with support for nesting features. GFF is also commonly used to store only biological features, and not the primary sequence.
These differences have some consequences in how you will deal with GFF:
- Files are first examined to determine available annotations and define items of interest.
- Sequences will often be parsed separately, from an associated FASTA file.
- Parsing needs to consider available memory, which can be quickly used up on files with many annotations. This problem can be solved via two methods:
- Limiting parsing to features of interest.
- Iterating over portions of the file.
The documentation below provides a practical guide to examining, parsing and writing GFF files in Python.