parameters: (cls, value, alternate='')
return_statement: return Resolve
docstring: Returns a dynamic value that defaults to an alternate.
  
      Args:
          value: The main value to resolve.
          alternate: The value to use if the main value does not resolve.
      Returns:
          value if it resolves, alternate otherwise.
docstring_summary: Returns a dynamic value that defaults to an alternate.
docstring_tokens: Returns a dynamic value that defaults to an alternate .
function: def Optional(cls, value, alternate=''):
      """Returns a dynamic value that defaults to an alternate.
  
      Args:
          value: The main value to resolve.
          alternate: The value to use if the main value does not resolve.
      Returns:
          value if it resolves, alternate otherwise.
      """
      def Resolve(base):
        try:
          return base.Substitute(value)
        except KeyError:
          return base.Substitute(alternate)
      return Resolve
function_tokens: def Optional ( cls , value , alternate = '' ) : def Resolve ( base ) : try : return base . Substitute ( value ) except KeyError : return base . Substitute ( alternate ) return Resolve