<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def load (self, filename):
 """Loads Command Definitions from the given YAML file into this Command Dictionary. """

        if self.filename is None:
            self.filename = filename

        stream = open(self.filename, "rb")
        for doc in yaml.load_all(stream):
            for table in doc:
                self.add(table)
        stream.close()