Question: Reciprocal Blast & Parse best hits
gravatar for Izal
2.1 years ago by
Izal10 wrote:

Hi everyone,

I'm novice doing reciprocal blast and I have spent a lot of time trying it. I don't know how to do a reciprocal blast and how to parse the best hits and compare & find matches. So, an advice would be a big help to me.

I need to do a reciprocal Blast in Python (Jupyter) to identify same proteins.

  • For that, first I make a db with the respective FASTA with the coding sequences.

    !makeblastdb -in $fastap_1 -dbtype 'prot'

    !makeblastdb -in $fastap_2 -dbtype 'prot'

  • Then, I run blastp for both files:

    blastp_ab = !blastp -query $fastap_1 -db $fastap_2 -out ab.txt

    blastp_ba = !blastp -query $fastap_2 -db $fastap_1 -out ba.txt

Up to here everything works. Now, I have to parse the blast results to collect best hits. I have tried it, but not even print "hello??"

If I pass as argument the file "ab.txt", the function "collect_best_hits" returns me an empty dictionary. And if I pass the handle "blastp_ab" as argument, "collect_best_hits" functions return me and advice of "blastall" and the empty dictionary:

no BLAST output. Check that blastall is in your PATH

{ }


filename = "ab.txt"

filename = blastp_ab

filename = open("ab.txt", "r")


The function contains:

import os import sys import csv import blastparser

 def collect_best_hits(filename):
   d = {}
        for n, record in enumerate(blastparser.parse_fp(filename)):
            print "hola"
            if n % 100 == 0:
                  print >>sys.stderr, 'loading 1 ...', n

            print "!-", n, record

            best_score = None
            for hit in record.hits:
                print "!- ", hit, len(record.hits)
                for match in hit.matches:
                    print "!- ", match, len(hit.matches)
                    query = record.query_name
                    if query.startswith('gi'):
                        query = query.split('|', 2)[2]
                    subject = hit.subject_name

                    score = match.score
                    print "!- ", score

                    # only keep the best set of scores for any query
                    if best_score and best_score > score:
                    best_score = score

                    x = d.get(query, [])
                    x.append((subject, score))
                    d[query] = x

                if best_score and best_score != score:
    except Exception as e:
    return d

What I'm doing wrong?

All help is welcome!

parse blast best hit reciprocal • 1.0k views
ADD COMMENTlink modified 2.1 years ago • written 2.1 years ago by Izal10
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