docs: def export(ctx, outfile, variant_type):
      """Export the variants of a loqus db
          
          The variants are exported to a vcf file
      """
      adapter = ctx.obj['adapter']
      version = ctx.obj['version']
      
      LOG.info("Export the variants from {0}".format(adapter))
      nr_cases = 0
  
      is_sv = variant_type == 'sv'
      existing_chromosomes = set(adapter.get_chromosomes(sv=is_sv))
      
      ordered_chromosomes = []
      for chrom in CHROMOSOME_ORDER:
          if chrom in existing_chromosomes:
              ordered_chromosomes.append(chrom)
              existing_chromosomes.remove(chrom)
      for chrom in existing_chromosomes:
          ordered_chromosomes.append(chrom)
      
      nr_cases = adapter.cases().count()
      LOG.info("Found {0} cases in database".format(nr_cases))
  
      head = HeaderParser()
      head.add_fileformat("VCFv4.3")
      head.add_meta_line("NrCases", nr_cases)
      head.add_info("Obs", '1', 'Integer', "The number of observations for the variant")
      head.add_info("Hom", '1', 'Integer', "The number of observed homozygotes")
      head.add_info("Hem", '1', 'Integer', "The number of observed hemizygotes")
      head.add_version_tracking("loqusdb", version, datetime.now().strftime("%Y-%m-%d %H:%M"))
      
      if variant_type == 'sv':
          head.add_info("END", '1', 'Integer', "End position of the variant")
          head.add_info("SVTYPE", '1', 'String', "Type of structural variant")
          head.add_info("SVLEN", '1', 'Integer', "Length of structural variant")
          
          
      for chrom in ordered_chromosomes:
          length = adapter.get_max_position(chrom)
          head.add_contig(contig_id=chrom, length=str(length))
  
      print_headers(head, outfile=outfile)
      
      for chrom in ordered_chromosomes:
          if variant_type == 'snv':
              LOG.info("Collecting all SNV variants")
              variants = adapter.get_variants(chromosome=chrom)
          else:
              LOG.info("Collecting all SV variants")
              variants = adapter.get_sv_variants(chromosome=chrom)
          LOG.info("{} variants found".format(variants.count()))
          for variant in variants:
              variant_line = format_variant(variant, variant_type=variant_type)
              # chrom = variant['chrom']
              # pos = variant['start']
              # ref = variant['ref']
              # alt = variant['alt']
              # observations = variant['observations']
              # homozygotes = variant['homozygote']
              # hemizygotes = variant['hemizygote']
              # info = "Obs={0}".format(observations)
              # if homozygotes:
              #     info += ";Hom={0}".format(homozygotes)
              # if hemizygotes:
              #     info += ";Hem={0}".format(hemizygotes)
              # variant_line = "{0}\t{1}\t.\t{2}\t{3}\t.\t.\t{4}\n".format(
              #     chrom, pos, ref, alt, info)
              print_variant(variant_line=variant_line, outfile=outfile)