"VALUE" = (SELECT MAX("VALUE") FROM in_raster)

"VALUE" = some_number

whereclause = "VALUE = " + str(arcpy.GetRasterProperties_management("C:/path_to_rasters/in_raster", "MAXIMUM"))
out_raster = arcpy.sa.ExtractByAttributes("C:/path_to_rasters/in_raster", whereclause)

[zonal_out] = in_raster