Michael Fairley Michael Fairley - 26 days ago 7
Python Question

Is there an easy way to pickle a python function (or otherwise serialize its code)?

I'm trying to transfer a function across a network connection (using asyncore). Is there an easy way to serialize a python function (one that, in this case at least, will have no side affects) for transfer like this?

I would ideally like to have a pair of functions similar to these:

def transmit(func):
obj = pickle.dumps(func)
[send obj across the network]

def receive():
[receive obj from the network]
func = pickle.loads(s)
func()

Answer

You could serialise the function bytecode and then reconstruct it on the caller. The marshal module can be used to serialise code objects, which can then be reassembled into a function. ie:

import marshal
def foo(x): return x*x
code_string = marshal.dumps(foo.func_code)

Then in the remote process (after transferring code_string):

import marshal, types

code = marshal.loads(code_string)
func = types.FunctionType(code, globals(), "some_func_name")

func(10)  # gives 100

A few caveats:

  • marshal's format (any python bytecode for that matter) may not be compatable between major python versions.

  • Will only work for cpython implementation.

  • If the function references globals (including imported modules, other functions etc) that you need to pick up, you'll need to serialise these too, or recreate them on the remote side. My example just gives it the remote process's global namespace.

  • You'll probably need to do a bit more to support more complex cases, like closures or generator functions.