Problem with demo.py in Tutorial

More a remark than a question, as I've found a way around it:

When I entered the demo example from http://www.fenics.org/wiki/Tutorial, I got the error message

fenics-test$ python demo.py
Calling FFC just-in-time (JIT) compiler, this may take some time.
Traceback (most recent call last):
  File "demo.py", line 13, in <module>
    u0 = Constant(mesh, 0.0)
TypeError: __init__() takes exactly 2 arguments (3 given)

Looking at the demos in dolfin-docs, I found I needed to change

u0 = Constant(mesh, 0.0)
to
u0 = Constant(0.0)

and later

f = Function(V, "500.0 * exp(-(pow(x[0] - 0.5, 2) + pow(x[1] - 0.5, 2)) / 0.02)")
to
f = Expression("500.0 * exp(-(pow(x[0] - 0.5, 2) + pow(x[1] - 0.5, 2)) / 0.02)")

to get it to work. I just started with python and FEniCS, do you think the problem is with my installation?