biostars 263478

answer.py

from pyfaidx import Fasta
with Fasta('input.fasta') as fasta:
  with open('pos.txt', 'r') as nucleotides:
    for line in nucleotides:
      chrom, pos = line.rstrip().split()
      nuc = fasta[chrom][int(pos)].seq
      print("{chrom}\t{pos}\t{nuc}".format(**locals()))