Is it possible to add a where clause with list comprehension?

There is no where statement but you can “emulate” it using for:

a=[0]
def f(x):
    a[0] += 1
    return 2*x

print [ (x, y) for x in range(5) for y in [f(x)] if y != 2 ]
print "The function was executed %s times" % a[0]

Execution:

$ python 2.py 
[(0, 0), (2, 4), (3, 6), (4, 8)]
The function was executed 5 times

As you can see, the functions is executed 5 times, not 10 or 9.

This for construction:

for y in [f(x)]

imitate where clause.