src/dunshire/errors.py

   1 """
   2 Errors that can occur when solving a linear game.
   3 """
   4
   5 from cvxopt import matrix
   6
   7
   8 def _pretty_format_dict(dictionary):
   9     """
  10     Return a pretty-formatted string representation of a dictionary
  11     containing CVXOPT matrices.
  12
  13     EXAMPLES:
  14
  15         >>> d = {'foo': 1.234, 'bar': matrix([1,2,3])}
  16         >>> print(_pretty_format_dict(d))
  17         bar:
  18           [ 1]
  19           [ 2]
  20           [ 3]
  21         foo: 1.234
  22
  23     """
  24     result = ''
  25     for (key, value) in dictionary.items():
  26         if isinstance(value, matrix):
  27             # Display matrices on their own lines, indented.
  28             result += '{:s}:'.format(key)
  29             colvec = '\n{!s}'.format(value)
  30             result += '\n  '.join(colvec.splitlines())
  31             result += '\n'
  32         else:
  33             result += '{:s}: {!s}\n'.format(key, value)
  34
  35     return result.rstrip('\n') # Kills trailing newlines on matrices.
  36
  37
  38 class GameUnsolvableException(Exception):
  39     """
  40     Every linear game has a solution (this follows from a general
  41     min-max theorem). If we can't solve the conic program associated
  42     with a linear game, then something is wrong with either the model of
  43     the input.
  44     """
  45     def __init__(self, solution_dict):
  46         """
  47         Create a new GameUnsolvableException object.
  48
  49         INPUT:
  50
  51         - ``solution_dict`` -- the solution dictionary returned from the
  52           cone program.
  53
  54         """
  55         super().__init__()
  56         self._solution_dict = solution_dict
  57
  58
  59     def __str__(self):
  60         """
  61         Return a string representation of this exception.
  62
  63         The returned representation highlights the "status" field of the
  64         CVXOPT dictionary, since that should explain what went
  65         wrong. The full CVXOPT solution dictionary is included after the
  66         status.
  67         """
  68         tpl = 'Solution failed with result "{:s}."\n' \
  69               'CVXOPT returned:\n  {!s}'
  70         cvx_lines = _pretty_format_dict(self._solution_dict).splitlines()
  71         cvx_str = '\n  '.join(cvx_lines) # Indent the whole dict by two spaces.
  72         return tpl.format(self._solution_dict['status'], cvx_str)