When extract water quality results using the Output object in pyswmm, users need to use the classes in swmm.toolkit.shared_enum as an argument for the method Output.link_attribute(). This will result in problem and failures when there are more than one pollutants defined in the SWMM input file. For example, when I have 4 pollutants, the swmm.toolkit.shared_enum.LinkAttribute class only has the attribute POLLUT_CONC_0, I've found that this problem can be fixed when I added POLLUT_CONC_1, POLLUT_CONC_2, POLLUT_CONC_3 manually in shared_enum.py (see also https://github.com/QianyangWang/Modified_swmmtoolkit_files.git). Maybe this problem can be easily fixed by some minor edits on the original code.