Beginner struggels with object-oriented programming to compute a time-, space- and u-dependent source term

[dokken]

Your are missing a super init in the expression class, see:

RecursionError: maximum recursion depth exceeded in the ft11_magnetostatics.py example of the "Solving PDEs in Python - The FEniCS tutorial Part 1"

The tutorial is out of date. Change your Permeability class to the following: class Permeability(UserExpression): # UserExpression instead of Expression def __init__(self, markers, **kwargs): super().__init__(**kwargs) # This part is new! self.markers = markers def eval_cell(self, values, x, cell): if self.markers[cell.index] == 0: values[0] = 4*pi*1e-7 # vacuum elif self.markers[cell.index] == 1: values[0] = 1e-5 # iron (shou…