Sliding Window with specific window size and step size in BioPython

Question

[adhirajnath14]

I have multiple sequences in a fasta file and I want to divide it into sliding window with window size 90 and step size 10. I have a python script as follows:

from Bio import SeqIO
 with open("my90_out.txt","w") as f:
    for seq_record in SeqIO.parse("myseq.fasta", "fasta"):
        for i in range(len(seq_record.seq) - 9) :
           f.writestrseq_record.id) + "\n")
           f.write(str(seq_record.seq[i:i+90]) + "\n") 
i

The code produces sequences with window size 90 but step size 1. I need to change the step size to 10. I know I have made a blunder in the for loop. Thanks in advance for the help.

[natasha.sernova]

See this script, try to change your step size accordingly:

How to extract short sequence from FASTA file with certain step size?

Answer 1

[Joe]

Since your range() call, will give you i equal to all the integers in the range of the sequence length, you need to change the step size, you can do this with an optional argument within range() itself: range(start, stop, step).

https://www.pythoncentral.io/pythons-range-function-explained/

Try changing your loop to something like:

for seq in SeqIO.parse("Genes1.fasta", "fasta"):
     for i in range(0, len(seq.seq)-9, 10):
         printseq.id + "\n")
         print(str(seq.seq[i:i+90] + "\n"))

(I've done away with the file openings and closings for ease, but you can just sub those back in for the print statements.