Python (single expression)

Now, while this is quite easy to figure out for Pythoneers, others might find it at least interesting. Who doesn't love underscores? Ideone

(lambda ______________:(lambda ______,_______,________:(lambda _____:(lambda _,___,__,____,_____________:(lambda _________,__________:(lambda ___________,____________:___________(____________,____[_________**(_________+__________)-__________::_________+_________+_________]+_[__________::_________]+__[_________+__________])(____________,______________))((lambda _,__:________(______(_))[__]),(________(__import__(_[_________]+__[_________*_________+__________]+_[_________]))[_[_________:_________+_________]+___[__________/_________]+__[__________]+_____(u'')[__________/_________]+_[_________+__________]])))((_____________(_)+_____________(_))/_____________(_),_____________(_)/_____________(_)))(_____([]),_____({}),_____(None),_____({}.__iter__),lambda _:len(_)))(lambda _:_______(______(_))))((lambda _:_.__class__),(lambda _:_.__name__),(lambda _:_.__dict__)))('Just another Python Hacker\n')

An indented version if you prefer:

(lambda ______________:
    (lambda ______,_______,________:
        (lambda _____:
            (lambda _,___,__,____,_____________:
                (lambda _________,__________:
                    (lambda ___________,____________:
                        ___________(____________,____[_________**(_________+__________)-__________::_________+_________+_________]+_[__________::_________]+__[_________+__________])(____________,______________)) (
                        (lambda _,__:________(______(_))[__]),
                        (________(__import__(_[_________]+__[_________*_________+__________]+_[_________]))[_[_________:_________+_________]+___[__________/_________]+__[__________]+_____(u'')[__________/_________]+_[_________+__________]]))) (
                    (_____________(_)+_____________(_))/_____________(_),
                    _____________(_)/_____________(_))) (
                _____([]),
                _____({}),
                _____(None),
                _____({}.__iter__),
                lambda _:len(_))) (
            lambda _:_______(______(_)))) (
        (lambda _:_.__class__),
        (lambda _:_.__name__),
        (lambda _:_.__dict__)))('Just another Python Hacker\n')