Python program accepting FASTA and BLAST, outputting in XML then returning IDs of all sequences

Ok. The assignment was to write a program which accepts an input argument of a FASTA file and prints the hit_id of all found sequences using three functions: run_blast (accepting the FASTA and optional input for BLAST, then using subprocess executes BLAST with BLAST output in XML format), read_blast (accepts the above BLAST XML file and returns IDs of sequences), and main (contains main processes the script will execute).

After 4 hours, all I can come up with is this:

import subprocess
from Bio.Blast import NCBIXML
def run_blast(fasta_filename,blastoutput):
    f=open(fasta_filename,'r')###opening the file with reading access           
    lines=f.read() ###lines equates to reading                                  
    col=lines.split("\n")###splits first and second lines                       
    sequence=col[1] ###gives this second column a name                          
    return sequence ###returns the answer of the second line of the FASTA       
fasta_filename='RBP1a.fa'###defining file names                                 
blastoutput='RBP1a.xml'
subprocess.call(['blastn','-query',"fasta_filename",'-db','nt','-outfmt','5','-\
out','blastoutput']) ###blast output in xml form                                
from Bio.Blast import NCBIXML
record=NCBIXML.read(open("blastoutput"))

def read_blast(blastoutput):

#####I don't even know what to put in order to extract the sequences from the XML file. Something about the order isn't correct here.