code: def getFasta(opened_file, sequence_name):
      
  
      lines = opened_file.readlines()
      seq=str("")
      for i in range(0, len(lines)):
          line = lines[i]
          if line[0] == ">":
              fChr=line.split(" ")[0].split("\n")[0]
              fChr=fChr[1:]
              if fChr == sequence_name:
                  s=i
                  code=['N','A','C','T','G']
                  firstbase=lines[s+1][0]
                  while firstbase in code:
                      s=s + 1
                      seq=seq+lines[s]
                      firstbase=lines[s+1][0]
  
      if len(seq)==0:
          seq=None
      else:
          seq=seq.split("\n")
          seq="".join(seq)
  
      return seq
docs: Retrieves a sequence from an opened multifasta file
  
      :param opened_file: an opened multifasta file eg. opened_file=open("/path/to/file.fa",'r+')
      :param sequence_name: the name of the sequence to be retrieved eg. for '>2 dna:chromosome chromosome:GRCm38:2:1:182113224:1 REF' use: sequence_name=str(2)
  
      returns: a string with the sequence of interest