Can I have an ellipsis at the beginning of the line in a Python doctest?

You can update the ELLIPSIS_MARKER for your test so that ... does not get confused with the line continuation dots:

def foo():
    """
    >>> import doctest
    >>> doctest.ELLIPSIS_MARKER = '-ignore-'
    >>> foo()
    hello world
    >>> foo() # doctest: +ELLIPSIS
    -ignore- world
    """
    print "hello world"

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

Disclaimer: the example above works when doctests are run as

$ py.test --doctest-module foo.py

or

$ python foo.py

However, for reasons I don't understand it does not work when running doctests via

$ python -m doctest foo.py

Here's a quick and dirty hack for you:

def foo():
    """
    >>> foo() # doctest: +ELLIPSIS
    [...] world
    """
    print "hello world"

if __name__ == "__main__":
    import doctest

    OC = doctest.OutputChecker
    class AEOutputChecker(OC):
        def check_output(self, want, got, optionflags):
            from re import sub
            if optionflags & doctest.ELLIPSIS:
                want = sub(r'\[\.\.\.\]', '...', want)
            return OC.check_output(self, want, got, optionflags)

    doctest.OutputChecker = AEOutputChecker
    doctest.testmod()

This still understands the normal ( ... ) ellipsis, but it adds a new one ( [...] ) that doesn't raise the line start ambiguity.

It would be seriously hard for doctest to guess whether there is a line continuation pending or whether its a line start ellipsis - it can be done, in theory, if you subclass DocTestParser to do that work but it probably won't be fun.

In complex situations you should probably roll your own DocTestRunner that would use the new OutputChecker and use that instead of the normal testmod but this should do in simple scenarios.