output_description: Prints the number of alphabetical letters in the following format:
  
      
      
      a : _The number of 'a'_
      b : _The number of 'b'_
      c : _The number of 'c'_
        .
        .
      z : _The number of 'z'_
input_description: A sentence in English is given in several lines.
attempt: import sys
  
  alp = [
      ["a", 0],
      ["b", 0],
      ["c", 0],
      ["d", 0],
      ["e", 0],
      ["f", 0],
      ["g", 0],
      ["h", 0],
      ["i", 0],
      ["j", 0],
      ["k", 0],
      ["l", 0],
      ["m", 0],
      ["n", 0],
      ["o", 0],
      ["p", 0],
      ["q", 0],
      ["r", 0],
      ["s", 0],
      ["t", 0],
      ["u", 0],
      ["v", 0],
      ["w", 0],
      ["x", 0],
      ["y", 0],
      ["z", 0],
  ]
  for line in sys.stdin:
      s = line.lower()
      for i in range(len(s)):
          for j in range(len(alp)):
              if s[i] == alp[j][0]:
                  alp[j][1] += 1
                  break
  for i in range(len(alp)):
      print("{0} : {1}".format(alp[i][0], alp[i][1]))
  
problem_description: Counting Characters
  
    
  
  Write a program which counts and reports the number of each alphabetical
  letter. Ignore the case of characters.
samples: [{"input": "This is a pen.", "output": "a : 1\n    b : 0\n    c : 0\n    d : 0\n    e : 1\n    f : 0\n    g : 0\n    h : 1\n    i : 2\n    j : 0\n    k : 0\n    l : 0\n    m : 0\n    n : 1\n    o : 0\n    p : 1\n    q : 0\n    r : 0\n    s : 2\n    t : 1\n    u : 0\n    v : 0\n    w : 0\n    x : 0\n    y : 0\n    z : 0"}]