<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def list_probes():
 """Return the list of built-in probes."""

    curdir = op.realpath(op.dirname(__file__))
    return [op.splitext(fn)[0] for fn in os.listdir(op.join(curdir, 'probes'))
            if fn.endswith('.prb')]