old_contents: def mutate(csv_data, exceptions_file, environ):
  
      with open(exceptions_file) as f:
         for exception in f:
            try:
               hostname, id = exception.split()
            except ValueError:
               continue
            # commented lines:
            if hostname[0] = '#':
               continue
            # don't do anything if we don't have matches for the hostname
            if not hostname in csv_data.host_to_vulns:
               continue
            csv_data.host_to_vulns[hostname] = filter( lambda vuln: vuln != id, csv_data.host_to_vulns[hostname] )
            if not csv_data.host_to_vulns[hostname]:
               del csv_data.host_to_vulns[hostname]
      
      # rebuild vuln_to_hosts
      csv_data.rebuild_vuln_to_hosts() 
  
new_contents: def mutate(csv_data, exceptions_file, environ):
  
      with open(exceptions_file) as f:
         for exception in f:
            try:
               hostname, id = exception.split()
            except ValueError:
               continue
            # commented lines:
            if hostname[0] == '#':
               continue
            # don't do anything if we don't have matches for the hostname
            if not hostname in csv_data.host_to_vulns:
               continue
            csv_data.host_to_vulns[hostname] = filter( lambda vuln: vuln != id, csv_data.host_to_vulns[hostname] )
            if not csv_data.host_to_vulns[hostname]:
               del csv_data.host_to_vulns[hostname]
      
      # rebuild vuln_to_hosts
      csv_data.rebuild_vuln_to_hosts() 
  
subject: Fix typo in comparison