old_contents: #
  # Copyright 2014, NICTA
  #
  # This software may be distributed and modified according to the terms of
  # the BSD 2-Clause license. Note that NO WARRANTY is provided.
  # See "LICENSE_BSD2.txt" for details.
  #
  # @TAG(NICTA_BSD)
  #
  
  '''Various helpers for doing advanced things with dictionaries.'''
  
  def get_fields(s):
      '''Return a set of field names referenced as formatting keys in the given
      string. I thought there would be an easier way to get this, but I can't
      find one. E.g. get_fields('%(hello)s %(world)s') returns
      set('hello', 'world').'''
      class FakeDict(dict):
          def __init__(self):
              super(FakeDict, self).__init__()
              self.referenced = set()
          def __getitem__(self, key):
              self.referenced.add(key)
              return ''
      f = FakeDict()
      s % f # Value deliberately discarded
      return f.referenced
  
  class Guard(object):
      '''Representation of a condition required for some action. See usage in
      Template.py.'''
      def __init__(self, guard_fn):
          self.guard_fn = guard_fn
  
      def __call__(self, arg):
          return self.guard_fn(arg)
  
new_contents: #
  # Copyright 2014, NICTA
  #
  # This software may be distributed and modified according to the terms of
  # the BSD 2-Clause license. Note that NO WARRANTY is provided.
  # See "LICENSE_BSD2.txt" for details.
  #
  # @TAG(NICTA_BSD)
  #
  
  '''Various helpers for doing advanced things with dictionaries.'''
  
  import re
  
  def get_fields(s):
      '''Return a set of field names referenced as formatting keys in the given
      string. I thought there would be an easier way to get this, but I can't
      find one. E.g. get_fields('%(hello)s %(world)s') returns
      set('hello', 'world').'''
      return set(re.findall(r'%\(([^)]+)\)', s))
  
  class Guard(object):
      '''Representation of a condition required for some action. See usage in
      Template.py.'''
      def __init__(self, guard_fn):
          self.guard_fn = guard_fn
  
      def __call__(self, arg):
          return self.guard_fn(arg)
  
subject: Support non-string formats in `get_fields`.