How to have hidden setup code for doctests

example.rst

This code is executed, but not rendered

This code is both executed by doctest and rendered in the output document

>>> datetime.datetime.fromtimestamp(0)
datetime.datetime(1970, 1, 1, 1, 0)

gistfile1.txt

$ python -m doctest -v example.rst
Trying:
    import datetime
Expecting nothing
ok
Trying:
    datetime.datetime.fromtimestamp(0)
Expecting:
    datetime.datetime(1970, 1, 1, 1, 0)
ok
1 items passed all tests:
   2 tests in fred.rst
2 tests in 1 items.
2 passed and 0 failed.
Test passed.