<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def tenant_exists(self, keystone, tenant):
 """Return True if tenant exists."""

        self.log.debug('Checking if tenant exists ({})...'.format(tenant))
        return tenant in [t.name for t in keystone.tenants.list()]