gistfile1.py

import functools
import inspect

# OMG, what have I done!? (Don't read this bit. Ever.)

class inject(object):
    @classmethod
    def require(__cls, *args):
        def decorator(func):
            functools.wraps(func)
            def wrapper(**kwargs):
                required_args = [arg for arg in args if arg not in kwargs]
                if required_args:
                    raise Exception("Missing required args {} for function {}".format(
                            ', '.join(required_args),
                            func.__name__)
                        )
                members = inspect.getmembers(func)
                __func_code = [v for k, v in members if k == '__code__'][0]
                __func_globals = [v for k, v in members if k == 'func_globals'][0]
                def real(**kw):
                    exec ';'.join('{}={}'.format(arg, kw[arg]) for arg in args) in locals(), __func_globals
                    __func_globals.update(locals())
                    return eval(__func_code, __func_globals)
                return real(**kwargs)
            if wrapper.__doc__:
                wrapper.__doc__ = 'Requires {}\n{}'.format(', '.join(args), wrapper.__doc__)
            else:
                wrapper.__doc__ = 'Requires {}'.format(', '.join(args))
            return wrapper
        return decorator


# Usage

@inject.require('r1', 'r2')
def foo1():
    print 'r1:', r1
    print 'r2:', r2
    print "and also in kw", kw
    foo2(**kw)
    return "har har" # return values work too
    

@inject.require('r3', 'r1')
def foo2():
    print "Look ma, r3 as a var:", r3
    print "AND in kw['r3']:",kw['r3']
    


retval = foo1(r1=1, r2=2, r3=3, r4=4)