#!/usr/bin/env python3

import sys

# first argument is script name
# second should be fasta path
# third argument should be the text to prepend to the seq ids
# fourth argument should be the path to save the fasta at
originalFastaPath = sys.argv[1]
textToPrepend = sys.argv[2]
newFastaPath = sys.argv[3]

newFastaString = ""

with open(originalFastaPath) as fp:
    line = fp.readline()
    cnt = 1
    while line:
        if line.startswith(">"):
            id = ">" + textToPrepend + "_" + line[1:]
        else:
            sequence = line
            newFastaString += id + sequence
        line = fp.readline()
        cnt += 1

f = open(newFastaPath, "w")
f.write(newFastaString)