Sharing locally defined modules / objects to a remote head


As already mentioned in #7133 and #3116, it is currently not possible to use any python object defined in local modules that are not available on the PYTHONPATH of the remote node(s).

IMHO, this is a major issue for using Ray within a research or fast-development context (e.g. data science), where you need to be able to quickly rerun code with minor modifications.
PySpark allows you to upload your custom python modules dynamically so that your code is available to every worker with the addFile method.

The Ray cookbooks for cloud clusters (AWS, GCS, Azure) allow you to specify which local folders you wish to copy to the remote machines, but that is not dynamical.

I think it should be possible to implement a simple API integration based on the existing Ray machinery that allows you to serialize a selection of files/folders and dispatch them to all remote nodes, so that any failed import statement run on the remote node will fallback to try to be resolved using these files.

I will try to do it myself and then make a PR or share a recipe. Please let me know if there is already a dynamical solution or why it is not possible.

Thanks a lot,


If you are planning to contribute this type of feature (that needs scoping), it’ll be nice if you can create a 1~2 pages design doc (which includes motivation, API specs, and implementation details) and post it on Ray’s Github issue page.

Here’s my recipe!

@sangcho unfortunately I do not have time to follow-up with a design proposal and clean PR.
I won’t create a PR then but just share my (dirty) solution here hoping that another contributor can build on it.

import os
import sys
import importlib
from time import sleep
import tempfile
from glob import glob

import ray

def remote_import(paths, wait=10):
    """Dynamically copy and import local custom modules and packages to all Ray workers

    Call this function after starting Ray up but before executing any remote operation (task or actor) that depends
     on the custom modules.

    The modules/packages are copied and imported every time the function is called,
     even if the local files have changed. Only .py files will be copied, any other extension will be ignored.

    The actual files will exist on a secure temporary folder on the remote machine just for the time needed to
    import them to the global namespace, then they are deleted.

    After the function returns, you may run any kind of import statement on the remote workers
    as if the packages were installed there. Please note that this is obtained with a rather dirty hack,
    polluting the global namespace. Be sure that none of the custom package names collides with other packages.

    :param paths: iterable of all locations you want to scan for python packages and modules.
    :param wait: number of seconds to wait for all workers to complete the module copying and loading.
    Since the underlying Ray method run_function_on_all_workers does not allow you to explicitly wait for
    these tasks to complete. Defaults to 10.
    copy_to_remote = {}

    for module_path in paths:  # /look/here/for/packages
        for filename in glob(os.path.join(module_path, '**', '*.py'), recursive=True):
            with open(filename) as f:
                # /look/here/for/packages/my_package/ ==> my_package/
                subpath = filename.replace(module_path, '').strip('/')
                copy_to_remote[subpath] = ray.put(  # the file content is sent to Ray object store

    # This function will run on every worker
    def on_remote(_):

        modules_to_be_imported = set()

        with tempfile.TemporaryDirectory(prefix='ray_custom_remote_modules') as temp_folder:
            # Retrieve files from Ray object store and copies them into a local tempfolder (including subfolders).
            for subpath, content_id in copy_to_remote.items():

                subpath_chunks = subpath.replace('.py', '').split(os.sep)  # ['package', 'subpackage', 'module']
                for i in range(len(subpath_chunks)):
                    # ['package', 'package.subpackage',      'package.subpackage.module'] will be added to global namespace

                target_path = os.path.join(temp_folder, subpath)
                os.makedirs(os.path.dirname(target_path), exist_ok=True)
                with open(target_path, 'w+') as f:

            sys.path.append(temp_folder)  # Add tempfolder to the sys path
            importlib.invalidate_caches()  # Clear import caches so that the new folder can be seen and read

            for module_name in modules_to_be_imported:
                module = importlib.import_module(module_name)  # Programmatically import the module
                module = importlib.reload(module)  # (in case files have been modified, this will re-read them)
                print('Importing', module_name)
                globals()[module_name] = module  # available to global namespace

            # tempfolder is deleted


Thanks for a lot the solution! Is there a recent PR that cover this issue?

Not that I know of, sorry. I never had time for a proper PR.