old_contents: from collections import Counter
  
  if __name__ == '__main__':
  
      with open('data/rosalind_dna.txt', mode='r') as f:
          sequence = f.read()
  
      counts = Counter(sequence)
  
      print '%d %d %d %d' % (counts['A'], counts['C'], counts['G'], counts['T'])
  
new_contents: """
  A string is simply an ordered collection of symbols selected from some alphabet and formed into a word;
  the length of a string is the number of symbols that it contains.
  
  An example of a length 21 DNA string (whose alphabet contains the symbols 'A', 'C', 'G', and 'T') is
  "ATGCTTCAGAAAGGTCTTACG."
  
  Given: A DNA string s of length at most 1000 nt.
  
  Return: Four integers (separated by spaces) counting the respective number of times that the symbols
  'A', 'C', 'G', and 'T' occur in s.
  """
  
  from collections import Counter
  
  if __name__ == '__main__':
  
      with open('data/rosalind_dna.txt', mode='r') as f:
          sequence = f.read()
  
      counts = Counter(sequence)
  
      print '%d %d %d %d' % (counts['A'], counts['C'], counts['G'], counts['T'])
  
subject: Add description to problem1.py