mpython.py

#!/usr/bin/python

from ast import *
import sys

def name(x, ctx):
  return Name(id = x, ctx = ctx, lineno = 0, col_offset = 0)

def call(f, *args):
  f = name(f, Load())
  return Call(func = f, args = list(args), lineno = 0,
              col_offset = 0, keywords = [], vararg = None)

def func(args, body):
  return Lambda(args = arguments(args = args, defaults = []),
                body = body, vararg = None, lineno = 0, col_offset = 0)

unit = Tuple(elts = [], lineno=0, col_offset = 0, ctx = Load())

def transform(elt, generators):
  elt = call("__singleton__", elt)

  for generator in generators[-1::-1]:
    for i in generator.ifs[-1::-1]:
      elt = call("__concatMap__",
                 func([name('_', Param())], elt),
                 IfExp(i,
                    call('__singleton__', unit),
                    call('__fail__'), lineno=0, col_offset=0))

    elt = call("__concatMap__",
               func([name(generator.target.id, Param())], elt),
               generator.iter)
  return elt

class RewriteComp(NodeTransformer):
  def visit_ListComp(self, node):
    return transform(RewriteComp().visit(node.elt),
                     [RewriteComp().visit(generator) for generator in node.generators])

def __concatMap__(f, x):
  return [z for y in x for z in f(y)]

def __singleton__(x):
  return [x]

def __fail__():
  return []

source = open(sys.argv[1]).read()
e = compile(source, "<string>", "exec", PyCF_ONLY_AST)
e = RewriteComp().visit(e)
f = compile(e, sys.argv[1], "exec")
print f
exec f
print "Done"