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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _consumers(self):
 """ Gets consumers from Lambda environment variables prefixed with CONSUMER_KEY_SECRET_. For example, given a consumer key of foo and a shared secret of bar, you should have an environment variable CONSUMER_KEY_SECRET_foo=bar. :return: consumers map :raises: LTIException if environment variables are not found """

        consumers = {}
        for env in os.environ:
            if env.startswith('CONSUMER_KEY_SECRET_'):
                key = env[20:]  # Strip off the CONSUMER_KEY_SECRET_ prefix
                # TODO: remove below after live test
                # consumers[key] = {"secret": os.environ[env], "cert": 'NA'}
                consumers[key] = {"secret": os.environ[env], "cert": None}
        if not consumers:
            raise LTIException("No consumers found. Chalice stores "
                               "consumers in Lambda environment variables. "
                               "Have you created the environment variables?")
        return consumers