Re-serializing values and functions into a new environment in Python

Question

I'm interested in moving a "session" across a boundary where I can only pass text.

I've been using Dill and this ALMOST seems to work.

import dill
from base64 import urlsafe_b64encode


def fun1():
    value_one = "abcdef"

    def sub_fun_one(x):
        return x * x

    __context_export = {}
    for val in globals():
        if not val.startswith("_"):
            __context_export[val] = dill.dumps(globals()[val])

    for val in locals():
        if not val.startswith("_"):
            __context_export[val] = dill.dumps(locals()[val])

    # __context_export["globals"] = dill.dumps(globals())
    # __context_export["locals"] = dill.dumps(locals())
    b64_string = str(urlsafe_b64encode(dill.dumps(__context_export)), encoding="ascii")

    print(b64_string)


fun1()

This outputs 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-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" as expected.

But in the second function - mocked up here - "value_one" doesn't seem to work at all.

import dill
from base64 import urlsafe_b64decode


def fun2(import_string):
    __base64_decode = urlsafe_b64decode(import_string)
    __context_import_dict = dill.loads(__base64_decode)
    # __globals_import = dill.loads(__context_import_dict["globals"])
    # __locals_import = dill.loads(__context_import_dict["locals"])
    print(__context_import_dict)

    for k in __context_import_dict:
        print(f"local = {k}")
        if locals().get(k) is None:
            g = dill.loads(__context_import_dict[k])
            locals()[k] = g

    print(value_one)
    print(f"Square value: {sub_fun_one(5)}")

import_value = "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-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"
fun2(import_value)

I'd prefer to do this more elegantly than eval 'k = v' because that will be hard to reserialize functions and dictionaries into.

Is this possible?

---

To be clear, I've read about the dangers of modifying locals() and I do NOT want to do this. But I also cannot rewrite the code that I'm accessing elsewhere to use a custom dict.

E.g. in fun2, I can NOT change print(value_one) to print(my_dict['value_one'])

Answer 1

Ok, so it APPEARS that doing the following works:

    for k in __context_import_dict:
        if globals().get(k) is None:
            globals()[k] = dill.loads(__context_import_dict[k])

What kind of pain am i signing myself up for?

Answer 2

From the Python documentation about locals():

Note: The contents of this dictionary should not be modified; changes may not affect the values of local and free variables used by the interpreter.

Function namespaces are not commmon dictionaries like module namespaces for performance reasons. I was bitten by this same quirk just yesterday.