Reassign scalar value within for loop

2

Consider the following:

from dolfin import *
import time

mesh = UnitSquareMesh(10,10)
V = FunctionSpace(mesh, "CG", 1)
u, v = TrialFunction(V), TestFunction(V)
alpha = Constant(1)
a = alpha*inner(u, v)*dx
for i in range(4):
    alpha.assign(i)
    start = time.time()
    A = assemble(a)
    end = time.time()
    print(end-start,  A.norm("frobenius"))

This produces

Calling FFC just-in-time (JIT) compiler, this may take some time.
Calling FFC just-in-time (JIT) compiler, this may take some time.
Calling FFC just-in-time (JIT) compiler, this may take some time.
Calling FFC just-in-time (JIT) compiler, this may take some time.
Calling FFC just-in-time (JIT) compiler, this may take some time.
Calling FFC just-in-time (JIT) compiler, this may take some time.
3.021070957183838 0.0
0.0009584426879882812 0.05157249482255294
0.0006306171417236328 0.10314498964510588
0.0006115436553955078 0.15471748446765718

As you can see, the form is only compiled once.