One-liner is a “compiler” that converts any Python file into a single line of code with the same functionality. Really, just one line! No newlines or semicolons allowed!

Take a look at the interactive demo to learn more about how it works.

Before:

def guess_my_number(n):
    while True:
        user_input = raw_input("Enter a positive integer to guess: ")
        if len(user_input)==0 or not user_input.isdigit():
            print "Not a positive integer!"
        else:
            user_input = int(user_input)
            if user_input > n:
                print "Too big! Try again!"
            elif user_input < n:
                print "Too small! Try again!"
            else:
                print "You win!"
                return True
guess_my_number(42)

After:

(lambda __builtin__: (lambda __print, __y, d: [(lambda ___: None)(d.guess_my_number(42)) for d.guess_my_number in [(lambda n:[(__y(lambda __this: (lambda d: (lambda __after: [(lambda __after: (lambda ___: __after(d))(__print('Not a positive integer!')) if (d.len(d.user_input)==0 or (not d.user_input.isdigit())) else [(lambda __after: (lambda ___: __after(d))(__print('Too big! Try again!')) if d.user_input>d.n else (lambda __after: (lambda ___: __after(d))(__print('Too small! Try again!')) if d.user_input<d.n else (lambda ___: d.True)(__print('You win!')))(lambda d: __after(d)))(lambda d: __after(d)) for d.user_input in [(d.int(d.user_input))]][0])(lambda d: __this(d)) for d.user_input in [(d.raw_input('Enter a positive integer to guess: '))]][0] if d.True else __after(d))(lambda d: None))))(d) for d.n in [(n)]][0])]][0])(__builtin__.__dict__['print'],(lambda f: (lambda x: x(x))(lambda y: f(lambda *args: y(y)(*args)))),type('StateDict',(),__builtin__.__dict__)()))(__import__('__builtin__'))

See the code on GitHub.