title: Remove redundancy in help function
body: <p>I can write the arguments but I can't avoid writing a function 'help' to print it if the command does not present the correct arguments.</p>
  
  <p>Any suggestion will be appreciated. </p>
  
  <pre><code>def get_arguments():
      parser = argparse.ArgumentParser(prog = 'contig2genbank.py', usage= '\n\t%(prog)s [contig ID/ or list of contigs] [output prefix]' , description = "Split a .gbk (.gbff) file and retrieve the information of the contig of interest.",formatter_class=RawTextHelpFormatter)
      parser.add_argument('-s', required = False, type = str, help='Name of input file (mandatory with -g)', metavar='') # used to extract single contigs
      parser.add_argument('-l', required = False, type = str, help='Name of input file  when in list (mandatory)', metavar='') # when giving a list of genomes and contigs to be extracted; see above the list example
      parser.add_argument('-g', required = False, type = str, help='Name of genome file (mandatory with -i)', metavar='') # when using a single genome, -g is the name of genome file in .gbk (.gbff) format
      return parser.parse_args()
  
  
  def help():
      parser = argparse.ArgumentParser(prog = 'contig2genbank.py', usage= '\n\t%(prog)s [contig ID/ or list of contigs] [output prefix]' , description = "Split a .gbk (.gbff) file and retrieve the information of the contig of interest.",formatter_class=RawTextHelpFormatter)
      parser.add_argument('-s', required = False, type = str, help='Name of input file (mandatory with -g)', metavar='') # used to extract single contigs
      parser.add_argument('-l', required = False, type = str, help='Name of input file  when in list (mandatory)', metavar='') # when giving a list of genomes and contigs to be extracted; see above the list example
      parser.add_argument('-g', required = False, type = str, help='Name of genome file (mandatory with -i)', metavar='') # when using a single genome, -g is the name of genome file in .gbk (.gbff) format 
      parser.print_help()
  
  
  def main():
      args = get_arguments()  # check arguments
  
      if args.s and args.g:
          with open(args.g, "rU") as genome: #open(args.c + '.gbk','w') as outgbk:
              for record in SeqIO.parse(genome, "genbank"):
                  if args.s == record.id:
                      #with open(args.c + '.gbk','w') as outgbk:
                      SeqIO.write([record], open(record.id + ".gbk", "w"), "genbank")
          print record.id + ".gbk created."
  
      else:
          help()
  </code></pre>
  
  <p>What I expect is to avoid the duplication of lines in get_arguments and help functions.</p>