I need a python script to get a genbank file, with the intron-exons boundaries, and give me the sequences of these boundaries. I think it should be easy with biopython seqIO, but I don't know how to use it in that way.
As others have said, it would be good if you could explain the what features your genbank files have and exactly what you want to get from them. Presuming you have genomic DNA with "exon" features like this one and you want to get sequences either side of the exon-intron boundary you can do this:
from Bio import SeqIO
record = SeqIO.read("LDH.gb", "genbank")
exons = [f for f in record.features if f.type == "exon"]
for start in [e.location.start.position for e in exons]:
print record.seq[start - 1 : start + 1]
You should also check out the biopython tutorial which describes the SeqRecord and SeqFeature objects