Wrong code in an example in "Whats new in Kwant 1.3"
In the section Calculating charges and currents using the operator module of [https://kwant-project.org/doc/1/pre/whatsnew/1.3] the code
# create the operators Q = kwant.physics.LocalOperator(syst) J = kwant.physics.Current(syst)
does not apply to the new version of Kwant.