<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _unique_key(job):
 """Return a key to query our uniqueness mapping system. This makes sure that we use a consistent key between our code and selecting jobs from the table. """

    return unique_key(testtype=str(job['testtype']),
                      buildtype=str(job['platform_option']),
                      platform=str(job['platform']))