def eval(self, construct):
data = clips.data.DataObject(self._env)<EOL>if lib.EnvEval(self._env, construct.encode(), data.byref) != <NUM_LIT:1>:<EOL><INDENT>raise CLIPSError(self._env)<EOL><DEDENT>return data.value<EOL>
Evaluate an expression returning its value.

        The Python equivalent of the CLIPS eval command.