Assemble is an integration command.
If you want to evaluate a trial function at a given point, see for instance:
https://bitbucket.org/fenics-project/dolfin/src/43642bad27866a5bf4e8a117c87c0f6ba777b196/python/test/unit/fem/test_manifolds.py?at=master#test_manifolds.py-235,243
or
Evaluate_basis() gives strange results - #2 by kamensky (and the original post in the linked thread)