functionize.py

# coding: utf-8
import ast

class _MakeFunction(ast.NodeTransformer):
    def __init__(self, name, args, body):
        self.name = name
        self.args = args
        self.body = body

    def run(self):
        template = 'def {self.name}({self.args}): pass'.format(self=self)
        template_ast = ast.parse(template, mode='exec')
        return self.visit(template_ast)

    def visit_Pass(self, node):
        return ast.parse(self.body, mode='exec').body


class _ReturnLastResult(ast.NodeTransformer):
    def visit_FunctionDef(self, node):
        self.generic_visit(node)
        retval_assign = \
                ast.Assign(targets=[ast.Name(id='_retval_', ctx=ast.Store())],
                           value=ast.NameConstant(value=None))               
        retval_return = \
                ast.Return(value=ast.Name(id='_retval_', ctx=ast.Load()))
        node.body.insert(0, retval_assign)
        node.body.append(retval_return)
        return ast.fix_missing_locations(node)

    def visit_Expr(self, node):
        target = ast.Name(id='_retval_', ctx=ast.Store())
        assign = ast.copy_location(
                    ast.Assign(targets=[target], value=node.value), node)
        return assign


def functionize(name, args, body):
    functionized_ast = \
            _ReturnLastResult().visit(_MakeFunction(name, args, body).run())
    return compile(functionized_ast, '<string>', mode='exec')