<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def __output_path(toolchain, rule, output_dir):
 """Gets the output path for a file given the toolchain, rule and output_dir"""

    filename = '%s_%s.json' % (toolchain, rule)
    return os.path.join(output_dir, filename)