Why is importing a module breaking my doctest (Python 2.7)

Question

I tried to use a StringIO instance in a doctest in my class, in a Python 2.7 program. Instead of getting any output from the test, I get a response, "Got nothing".

This simplified test case demonstrates the error:

#!/usr/bin/env python2.7
# encoding: utf-8

class Dummy(object):
    '''Dummy: demonstrates a doctest problem

    >>> from StringIO import StringIO
    ... s = StringIO()
    ... print("s is created")
    s is created
    '''

if __name__ == "__main__":
    import doctest
    doctest.testmod()

Expected behaviour: test passes.

Observed behaviour: test fails, with output like this:

% ./src/doctest_fail.py
**********************************************************************
File "./src/doctest_fail.py", line 7, in __main__.Dummy
Failed example:
    from StringIO import StringIO
    s = StringIO()
    print("s is created")
Expected:
    s is created
Got nothing
**********************************************************************
1 items had failures:
   1 of   1 in __main__.Dummy
***Test Failed*** 1 failures.

Why is this doctest failing? What change to I need to make in order to be able to use StringIO-like functionality (a literal string with a file interface) in my doctests?

Answer 1

It's the continuation line syntax (...) that is confusing doctest parser. This works:

#!/usr/bin/env python2.7
# encoding: utf-8

class Dummy(object):
    '''Dummy: demonstrates a doctest problem

    >>> from StringIO import StringIO
    >>> s = StringIO()
    >>> print("s is created")
    s is created
    '''

if __name__ == "__main__":
    import doctest
    doctest.testmod()