input: 
  from typing import List, Dict
  
  def calculate_percent_mapped_rRNA(htseq_file: str, gtf_file: str) -> Dict[str, float]:
      """
      Calculate the percent of transcripts mapping to rRNA and MT for a given HTseq_counts file and GTF file.
      Return a dictionary with the percentages of rRNA and MT mapped reads.
      
      >>> calculate_percent_mapped_rRNA('C17_3_S20_Aligned.out.srt.bam_htseq_combined_counts.txt', 'Mus_musculus.GRCm38.84.gtf')
      {'Percent rRNA mapped reads': 10.523, 'Percent MT mapped reads': 5.213}
      """
  
output:     rRNA_count = 0
      MT_count = 0
      total_count = 0
  
      with open(htseq_file, 'r') as htseq:
          for line in htseq:
              if line.startswith('__'):
                  continue
              total_count += int(line.split('\t')[1])
  
      with open(gtf_file, 'r') as gtf:
          for line in gtf:
              if 'rRNA' in line:
                  rRNA_count += 1
              if 'MT' in line:
                  MT_count += 1
  
      percent_rRNA = (rRNA_count / total_count) * 100
      percent_MT = (MT_count / total_count) * 100
  
      return {'Percent rRNA mapped reads': percent_rRNA, 'Percent MT mapped reads': percent_MT}