Hi Christoph, This is a well-working code that computes conductance for graphene with 2 leads (conductance is now commented in the end). The issue appears at line 485. Loading the large package warning may be due to running from Eric6 Python IDE that I use. I have now the latest 1.4 Kwant version installed via pip3 , which added the necessity to remove the default values from "args" parameter list, as it's no longer supported As for ppa install, I might be doing something wrong: (Linux Mint 19 = Ubuntu bionic) sudo add-apt-repository ppa:kwant-project/ppa sudo apt-get update sudo apt-get install kwant returns: "Unable to locate package kwant" The test python3 -c 'import kwant; kwant.test(verbose=False)' returns 21 warnings: (see below) .local/lib/python3.6/site-packages/kwant/tests/test_plotter.py::test_map /home/sergey/.local/lib/python3.6/site-packages/numpy/lib/function_base.py:3652: RuntimeWarning: Invalid value encountered in percentile interpolation=interpolation) /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1300: RuntimeWarning: invalid value encountered in greater overflow_pct = 100 * np.sum(unmasked_data > new_vmax) / len(unmasked_data) /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1301: RuntimeWarning: invalid value encountered in less underflow_pct = 100 * np.sum(unmasked_data < new_vmin) / len(unmasked_data) .local/lib/python3.6/site-packages/kwant/tests/test_plotter.py::test_spectrum /home/sergey/.local/lib/python3.6/site-packages/mpl_toolkits/mplot3d/axes3d.py:1069: UserWarning: Axes3D.figure.canvas is 'None', mouse rotation disabled. Set canvas then call Axes3D.mouse_init(). "Axes3D.figure.canvas is 'None', mouse rotation disabled. " /home/sergey/.local/lib/python3.6/site-packages/numpy/core/fromnumeric.py:83: RuntimeWarning: invalid value encountered in reduce return ufunc.reduce(obj, axis, dtype, out, **passkwargs) .local/lib/python3.6/site-packages/kwant/tests/test_plotter.py::test_density_interpolation /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns .local/lib/python3.6/site-packages/kwant/tests/test_plotter.py::test_current_interpolation /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns /home/sergey/.local/lib/python3.6/site-packages/kwant/plotter.py:1684: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. field_out[field_slice] += magns .local/lib/python3.6/site-packages/kwant/tests/test_plotter.py::test_current /home/sergey/.local/lib/python3.6/site-packages/kwant/tests/test_plotter.py:522: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. plotter.current(syst, current, file=out) /home/sergey/.local/lib/python3.6/site-packages/kwant/tests/test_plotter.py:526: FutureWarning: Using a non-tuple sequence for multidimensional indexing is deprecated; use `arr[tuple(seq)]` instead of `arr[seq]`. In the future this will be interpreted as an array index, `arr[np.array(seq)]`, which will result either in an error or a different result. plotter.current(syst, current, ax=ax, file=out) .local/lib/python3.6/site-packages/kwant/tests/test_wraparound.py::test_symmetry /home/sergey/.local/lib/python3.6/site-packages/kwant/tests/test_wraparound.py:169: RuntimeWarning: `particle_hole` and `time_reversal` symmetries are set on the input builder. However they are ignored for the wrapped system, since Kwant lacks a way to express the existence (or not) of a symmetry at k != 0. wrapped = wraparound(syst) .local/lib/python3.6/site-packages/kwant/tests/test_wraparound.py::test_plot_2d_bands /home/sergey/.local/lib/python3.6/site-packages/numpy/core/fromnumeric.py:83: RuntimeWarning: invalid value encountered in reduce return ufunc.reduce(obj, axis, dtype, out, **passkwargs) -- Docs: http://doc.pytest.org/en/latest/warnings.html =================== 282 passed, 21 warnings in 51.40 seconds ===================