'Read configuration from environment variable.
The value of the environment variable must be the name
of a module to import.
Example:
>>> os.environ[\'CELERY_CONFIG_MODULE\'] = \'myapp.celeryconfig\'
>>> celery.config_from_envvar(\'CELERY_CONFIG_MODULE\')'

def config_from_envvar(self, variable_name, silent=False, force=False):

    module_name = os.environ.get(variable_name)
    if (not module_name):
        if silent:
            return False
        raise ImproperlyConfigured(ERR_ENVVAR_NOT_SET.strip().format(variable_name))
    return self.config_from_object(module_name, silent=silent, force=force)
