If you had
a) Taken the time to search the forum for this error, you would for instance have found the solution in this post RecursionError: maximum recursion depth exceeded in the ft11_magnetostatics.py example of the "Solving PDEs in Python - The FEniCS tutorial Part 1"
b) If it had not been the case that you could find the solution by searching the forum, please read Read before posting: How do I get my question answered?
as your question is way too vague for anyone to answer.