python - Why doesn't this set comprehension work?

Question

In Python 2.6.5, given this list mylist = [20, 30, 25, 20]

Why does this set comprehension not work?

>>> {x for x in mylist if mylist.count(x) >= 2}
  File "<stdin>", line 1
    {x for x in mylist if mylist.count(x) >= 2}
         ^
SyntaxError: invalid syntax

Thank you.

Answer 1

$ python2.6
>>> mylist = [20, 30, 25, 20]
>>> {x for x in mylist if mylist.count(x) >= 2}
  File "<stdin>", line 1
    {x for x in mylist if mylist.count(x) >= 2}
         ^
SyntaxError: invalid syntax

$ python2.7
>>> mylist = [20, 30, 25, 20]
>>> {x for x in mylist if mylist.count(x) >= 2}
set([20])

You can accomplish the results in python2.6 using an explicit set, and a generator:

>>> set(x for x in mylist if mylist.count(x) >= 2)
set([20])