Split fasta file
PLAN is a free online service for BLAST based sequence annotation provided by the Noble institute. At present the people that run PLAN limit user's queries to 1000 records. This recipe shows how to split a fasta file containing thousands of records into smaller files with filenames that include the range of records included in the file.
from Bio import SeqIO in_name = "huge_run.fasta" records = list(SeqIO.parse(open(in_name, 'r'), "fasta")) # How many files of exactly 1000 records can we make? nfiles = len(records)/1000 for filenumber in range(nfiles): split_min = filenumber*1000 split_max = ((filenumber+1)*1000)-1 seqs = records[split_min:split_max] out_name = ("_%s-%s." % (split_min+1, split_max+1)).join(in_name.split(".")) out_handle = open(out_name, 'w') SeqIO.write(seqs, out_handle, "fasta") out_handle.close() # That will make a bunch of files with 1000 records, but you will almost always # have some "dregs" to mop up. if len(records) / 1000 != 0: #checking for leftovers lsplit_min = (nfiles+1)*1000 last_name = ("_%s-%s." % (lsplit_min, len(records)-1)).join(in_name.split(".")) last_handle = open(last_name, 'w') lseqs = records[lsplit_min:-1] SeqIO.write(lseqs, last_handle, "fasta") last_handle.close() else: continue
How it works
The basic approach is do use SeqIO.parse() to read the contents of a fasta file into a list, then pick out subsets to write with SeqIO.write() . Perhaps the trickiest looking line is the one that sets each new file's name:
out_name = ("_%s-%s." % (split_min+1, split_max+1)).join(in_name.split("."))
which can be broken down thus:
>>> insert = "_%s-%s." % (1, 1000) >>> insert '_1-1000.' >>> split_name = "huge_run.fasta".split(".") ['huge_run', 'fasta'] >>>(insert).join(split_name) 'huge_run_1-1000.fasta'