code: def count_sequences(infile):
      '''Returns the number of sequences in a file'''
      seq_reader = sequences.file_reader(infile)
      n = 0
      for seq in seq_reader:
          n += 1
      return f count_sequences(infile):
      '''Returns the number of sequences in a file'''
      seq_reader = sequences.file_reader(infile)
      n = 0
      for seq in seq_reader:
          n += 1
      return n
docs: Returns the number of sequences in a file