annoregion2 = Annoregion2(fmt="gtf",gattr="gene_name",tattr="transcript_name",gidattr="gene_id",tidattr="transcript_id",genetypeattr="gene_type",transcripttypeattr="transcript_type",tanno="exon,CDS,UTR")
annoregion2.gtf2exons(gtf_filename) 
# then  all genes is in 
annoregion2.h  # which is a dict, include all genes,  key => value, key is geneid, value is corresponding Gene_instance