One-liner

Live demo at onelinepy.herokuapp.com!

Convert any Python file into a single line of code which has the same functionality.

No newlines allowed. No semicolons allowed, either.

Installation and Usage

$ git clone https://github.com/csvoss/oneliner
$ cd oneliner
$ python main.py target_file.py --debug
$ python target_file.ol.py

Examples

Before:

x = 3
y = 4
print (x < y < 5)

After:

(lambda __builtin__: (lambda __print, __y, d: [[__print(d.x<d.y<5) for d.y in [(4)]][0] for d.x in [(3)]][0])(__builtin__.__dict__['print'],(lambda f: (lambda x: x(x))(lambda y: f(lambda *args: y(y)(*args)))),type('StateDict',(),__builtin__.__dict__)()))(__import__('__builtin__'))

That line looks complicated, because we need some tricks to import the print function and to support certain tricks which are needed for more complicated features such as while and if. For a program as simple as this one, though, you can think of it as working this way:

(lambda x: (lambda y: print(x<y<5))(4))(3)

Before:

def f(x):
    return x+5
print f(13)

After:

(lambda __builtin__: (lambda __print, __y, d: [__print(d.f(13)) for d.f in [(lambda x:[(d.x+5) for d.x in [(x)]][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__'))

...or, if you want to think about something more simplified:

(lambda f: print(f(13)))(lambda x: x+5)

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__'))

FAQ

Oh dear God why?

Yeah. I'm sorry. But on the other hand, why not?

Can't you use semicolons?

That would be against the spirit of this exercise. Why pass up a perfectly good excuse to abuse lambda functions, ternary expressions, list comprehensions, and even the occasional Y combinator? Never pass up an opportunity to use the Y combinator.

Analysis

Output program size

O(n). No code is ever duplicated, so the one-lined code produced is linear in the size of the input code.

Time

I'm guessing it's slower, but no more than linearly so; I have yet to analyze this.

Tips

The one-lined code tends to contain many nested lambdas; if there are too many, Python will refuse to run it.

$ python main.ol.py
s_push: parser stack overflow
MemoryError

This can be fixed using pypy.

$ pypy main.ol.py

However, since while loops and for loops are implemented with recursion, you might encounter maximum recursion depth exceeded errors during runtime if your loops go on for too long.

To get around this, you can put

import sys
sys.setrecursionlimit(new_limit)

in your original Python code. (oneliner will not place this command in for you.)

Not Implemented

• classes and OOP
• from foo import *

Open Problems

• try/except/finally
• global variables
• with
• yield

Further Reading

• StackOverflow post about how functional programming helps with Python mastery
• On writing Python one-liners -- a similar idea