code: def get_qual(fastafile, suffix=QUALSUFFIX, check=True):
      
      qualfile1 = fastafile.rsplit(".", 1)[0] + suffix
      qualfile2 = fastafile + suffix
  
      if check:
          if op.exists(qualfile1):
              logging.debug("qual file `{0}` found".format(qualfile1))
              return qualfile1
          elif op.exists(qualfile2):
              logging.debug("qual file `{0}` found".format(qualfile2))
              return qualfile2
          else:
              logging.warning("qual file not found")
              return None
  
      return qualfile1
docs: Check if current folder contains a qual file associated with the fastafile