C.3 Chapter 3

1. Coding basic loops. If you work through this exercise, you'll wind up with code that looks like the following:

   >>> S = 'spam'
   >>> for c in S:
   ...     print ord(c)
   ...
   115
   112
   97
   109
   
   >>> x = 0
   >>> for c in S: x = x + ord(c)
   ...
   >>> x
   433
   
   >>> x = []
   >>> for c in S: x.append(ord(c))
   ...
   >>> x
   [115, 112, 97, 109]
   
   >>> map(ord, S)
   [115, 112, 97, 109]

2. Backslash characters. The example prints the bell character (\a) 50 times; assuming your machine can handle it, you'll get a series of beeps (or one long tone, if your machine is fast enough). Hey—we warned you.

3. Sorting dictionaries. Here's one way to work through this exercise; see Chapter 2 if this doesn't make sense:

   >>> D = {'a':1, 'b':2, 'c':3, 'd':4, 'e':5, 'f':6, 'g':7}
   >>> D
   {'f': 6, 'c': 3, 'a': 1, 'g': 7, 'e': 5, 'd': 4, 'b': 2}
   >>>
   >>> keys = D.keys()
   >>> keys.sort()
   >>> for key in keys:
   ...     print key, '=>', D[key]
   ...
   a => 1
   b => 2
   c => 3
   d => 4
   e => 5
   f => 6
   g => 7

4. Program logic alternatives. Here's how we coded the solutions; your results may vary a bit.

   1. L = [1, 2, 4, 8, 16, 32, 64]
      X = 5
      
      i = 0
      while i < len(L):
          if 2 ** X == L[i]:
              print 'at index', i
              break
          i = i+1
      else:
          print X, 'not found'

   2. L = [1, 2, 4, 8, 16, 32, 64]
      X = 5
      
      for p in L:
          if (2 ** X) == p:
              print (2 ** X), 'was found at', L.index(p)
              break
      else:
          print X, 'not found'

   3. L = [1, 2, 4, 8, 16, 32, 64]
      X = 5
      
      if (2 ** X) in L:
          print (2 ** X), 'was found at', L.index(2 ** X)
      else:
          print X, 'not found'

   4. X = 5
      L = []
      for i in range(7): L.append(2 ** i)
      print L
      
      if (2 ** X) in L:
          print (2 ** X), 'was found at', L.index(2 ** X)
      else:
          print X, 'not found'

   5. X = 5
      L = map(lambda x: 2**x, range(7))
      print L
      
      if (2 ** X) in L:
          print (2 ** X), 'was found at', L.index(2 ** X)
      else:
          print X, 'not found'