How do I efficiently filter computed values within a Python list comprehension?

Question

The Python list comprehension syntax makes it easy to filter values within a comprehension. For example:

result = [x**2 for x in mylist if type(x) is int]
<         


        

Answer 1

I will have a preference for:

itertools.ifilter(bool, (expensive(x) for x in mylist))

This has the advantage to:

• avoid None as the function (will be eliminated in Python 3): http://bugs.python.org/issue2186
• use only iterators.