Comparing two multi-fasta files of the same set of proteins with parser - to find and count mutations after treatment My task is to count the mutations  occurred in several proteins after a treatment. The sequences are all present in the two files in the same order. I opened both files with the FASTA parser (SeqIO.parse) in Biopython and I got all the proteins listed (separated before and after the treatment).

How can I zip the parsers together to count the mutations?

How can I count the mutations that occured after the treatment?

from Bio import SeqIO
for normal_samples in SeqIO.parse("/data/statistic/normal_samples", "fasta"):
    print(normal_samples.id)
    print(repr(normal_samples.seq))
    print(len(normal_samples))

for treated_samples in SeqIO.parse("/data/statistic/with_treatment", "fasta"):
    print(normal_samples.id)
    print(repr(normal_samples.seq))
    print(len(normal_samples))

dict_n_t = dict(zip(normal_samples &amp; treated_samples))
from Bio import SeqIO
for normal, treated in zip(SeqIO.parse("/data/statistic/normal_samples", "fasta"),
                           SeqIO.parse("/data/statistic/with_treatment", "fasta")):
    ... do stuff...


That's generally how you zip iterators together in python.