Allow loading checkpoints from urls (#1667)

* allow loading checkpoints from urls

* tmpdir_server fixture

* test cases for loading checkpoints from url

* dir => root_dir

* default map_location to None

* test case for resume_from_checkpoint

* changelog

* doc update

* monkeypatch TORCH_HOME to avoid caching

* Use a threading server with random ports so that it is easier to clean up

* test fixes

* pep8 fix

* ThreadingHTTPServer support in 3.6

* pep8 fix

* fix changelog

* separate tests for urls

* typo

Co-authored-by: Peter Yu <2057325+yukw777@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>

CHANGELOG.md

@@ -33,6 +33,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added a model hook `transfer_batch_to_device` that enables moving custom data structures to the target device ([1756](https://github.com/PyTorchLightning/pytorch-lightning/pull/1756))
 - Added [black](https://black.readthedocs.io/en/stable/) formatter for the code with code-checker on pull ([1610](https://github.com/PyTorchLightning/pytorch-lightning/pull/1610))
 - Added back the slow spawn ddp implementation as `ddp_spawn` ([#2115](https://github.com/PyTorchLightning/pytorch-lightning/pull/2115))
+- Added loading checkpoints from URLs ([#1667](https://github.com/PyTorchLightning/pytorch-lightning/issues/1667))
 
 ### Changed
 

pytorch_lightning/core/saving.py

@@ -10,6 +10,7 @@
 
 from pytorch_lightning import _logger as log
 from pytorch_lightning.utilities import rank_zero_warn, AttributeDict
+from pytorch_lightning.utilities.io import load as pl_load
 
 PRIMITIVE_TYPES = (bool, int, float, str)
 ALLOWED_CONFIG_TYPES = (AttributeDict, dict, Namespace)
@@ -52,10 +53,10 @@ def load_from_checkpoint(
         Primary way of loading a model from a checkpoint. When Lightning saves a checkpoint
         it stores the arguments passed to `__init__`  in the checkpoint under `module_arguments`
 
-        Any arguments specified through \*args and \*\*kwargs will override args stored in `module_arguments`.
+        Any arguments specified through \*args and \*\*kwargs will override args stored in `hparams`.
 
         Args:
-            checkpoint_path: Path to checkpoint.
+            checkpoint_path: Path to checkpoint. This can also be a URL.
             args: Any positional args needed to init the model.
             map_location:
                 If your checkpoint saved a GPU model and you now load on CPUs
@@ -131,9 +132,9 @@ def load_from_checkpoint(
                 y_hat = pretrained_model(x)
         """
         if map_location is not None:
-            checkpoint = torch.load(checkpoint_path, map_location=map_location)
+            checkpoint = pl_load(checkpoint_path, map_location=map_location)
         else:
-            checkpoint = torch.load(checkpoint_path, map_location=lambda storage, loc: storage)
+            checkpoint = pl_load(checkpoint_path, map_location=lambda storage, loc: storage)
 
         # add the hparams from csv file to checkpoint
         if tags_csv is not None:
@@ -162,7 +163,6 @@ def load_from_checkpoint(
 
     @classmethod
     def _load_model_state(cls, checkpoint: Dict[str, Any], *args, **kwargs):
-
         # pass in the values we saved automatically
         if cls.CHECKPOINT_KEY_HYPER_PARAMS in checkpoint:
             # todo add some back compatibility

pytorch_lightning/trainer/trainer.py

@@ -279,6 +279,7 @@ def __init__(
             truncated_bptt_steps: Truncated back prop breaks performs backprop every k steps of
 
             resume_from_checkpoint: To resume training from a specific checkpoint pass in the path here.
+                This can be a URL.
 
             profiler:  To profile individual steps during training and assist in
 

pytorch_lightning/trainer/training_io.py

@@ -102,6 +102,7 @@
     LightningDataParallel,
 )
 from pytorch_lightning.utilities import rank_zero_warn, parsing
+from pytorch_lightning.utilities.io import load as pl_load
 
 try:
     import torch_xla
@@ -287,7 +288,7 @@ def restore(self, checkpoint_path: str, on_gpu: bool):
         #     checkpoint = torch.load(checkpoint_path)
         # else:
         # load on CPU first
-        checkpoint = torch.load(checkpoint_path, map_location=lambda storage, loc: storage)
+        checkpoint = pl_load(checkpoint_path, map_location=lambda storage, loc: storage)
 
         # load model state
         model = self.get_model()

pytorch_lightning/utilities/io.py

@@ -0,0 +1,11 @@
+import torch
+
+from urllib.parse import urlparse
+
+
+def load(path_or_url: str, map_location=None):
+    parsed = urlparse(path_or_url)
+    if parsed.scheme == '':
+        # local file
+        return torch.load(path_or_url, map_location=map_location)
+    return torch.hub.load_state_dict_from_url(path_or_url, map_location=map_location)

tests/conftest.py

@@ -1,6 +1,9 @@
-from functools import wraps
+from functools import wraps, partial
+from http.server import SimpleHTTPRequestHandler
 
+import sys
 import pytest
+import threading
 import torch.multiprocessing as mp
 
 
@@ -17,3 +20,38 @@ def pytest_pyfunc_call(pyfuncitem):
 
         mp.spawn(wraps, (testfunction, testargs))
         return True
+
+
+@pytest.fixture
+def tmpdir_server(tmpdir):
+    if sys.version_info >= (3, 7):
+        Handler = partial(SimpleHTTPRequestHandler, directory=str(tmpdir))
+        from http.server import ThreadingHTTPServer
+    else:
+        # unfortunately SimpleHTTPRequestHandler doesn't accept the directory arg in python3.6
+        # so we have to hack it like this
+        import os
+
+        class Handler(SimpleHTTPRequestHandler):
+            def translate_path(self, path):
+                # get the path from cwd
+                path = super().translate_path(path)
+                # get the relative path
+                relpath = os.path.relpath(path, os.getcwd())
+                # return the full path from root_dir
+                return os.path.join(str(tmpdir), relpath)
+
+        # ThreadingHTTPServer was added in 3.7, so we need to define it ourselves
+        from socketserver import ThreadingMixIn
+        from http.server import HTTPServer
+
+        class ThreadingHTTPServer(ThreadingMixIn, HTTPServer):
+            daemon_threads = True
+
+    with ThreadingHTTPServer(('', 0), Handler) as server:
+        server_thread = threading.Thread(target=server.serve_forever)
+        # Exit the server thread when the main thread terminates
+        server_thread.daemon = True
+        server_thread.start()
+        yield server.server_address
+        server.shutdown()

tests/trainer/test_trainer.py

@@ -16,12 +16,16 @@
 from pytorch_lightning.core.saving import load_hparams_from_tags_csv, load_hparams_from_yaml, save_hparams_to_tags_csv
 from pytorch_lightning.loggers import TensorBoardLogger
 from pytorch_lightning.trainer.logging import TrainerLoggingMixin
+from pytorch_lightning.utilities.io import load as pl_load
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from tests.base import EvalModelTemplate
 
 
-def test_no_val_module(tmpdir):
+@pytest.mark.parametrize('url_ckpt', [True, False])
+def test_no_val_module(monkeypatch, tmpdir, tmpdir_server, url_ckpt):
     """Tests use case where trainer saves the model, and user loads it from tags independently."""
+    # set $TORCH_HOME, which determines torch hub's cache path, to tmpdir
+    monkeypatch.setenv('TORCH_HOME', tmpdir)
 
     model = EvalModelTemplate()
 
@@ -49,15 +53,19 @@ def test_no_val_module(tmpdir):
     # load new model
     hparams_path = tutils.get_data_path(logger, path_dir=tmpdir)
     hparams_path = os.path.join(hparams_path, 'hparams.yaml')
+    ckpt_path = f'http://{tmpdir_server[0]}:{tmpdir_server[1]}/{os.path.basename(new_weights_path)}' if url_ckpt else new_weights_path
     model_2 = EvalModelTemplate.load_from_checkpoint(
-        checkpoint_path=new_weights_path,
+        checkpoint_path=ckpt_path,
         hparams_file=hparams_path
     )
     model_2.eval()
 
 
-def test_no_val_end_module(tmpdir):
+@pytest.mark.parametrize('url_ckpt', [True, False])
+def test_no_val_end_module(monkeypatch, tmpdir, tmpdir_server, url_ckpt):
     """Tests use case where trainer saves the model, and user loads it from tags independently."""
+    # set $TORCH_HOME, which determines torch hub's cache path, to tmpdir
+    monkeypatch.setenv('TORCH_HOME', tmpdir)
 
     model = EvalModelTemplate()
 
@@ -82,8 +90,9 @@ def test_no_val_end_module(tmpdir):
     # load new model
     hparams_path = tutils.get_data_path(logger, path_dir=tmpdir)
     hparams_path = os.path.join(hparams_path, 'hparams.yaml')
+    ckpt_path = f'http://{tmpdir_server[0]}:{tmpdir_server[1]}/{os.path.basename(new_weights_path)}' if url_ckpt else new_weights_path
     model_2 = EvalModelTemplate.load_from_checkpoint(
-        checkpoint_path=new_weights_path,
+        checkpoint_path=ckpt_path,
         hparams_file=hparams_path
     )
     model_2.eval()
@@ -320,8 +329,11 @@ def test_model_freeze_unfreeze():
     model.unfreeze()
 
 
-def test_resume_from_checkpoint_epoch_restored(tmpdir):
+@pytest.mark.parametrize('url_ckpt', [True, False])
+def test_resume_from_checkpoint_epoch_restored(monkeypatch, tmpdir, tmpdir_server, url_ckpt):
     """Verify resuming from checkpoint runs the right number of epochs"""
+    # set $TORCH_HOME, which determines torch hub's cache path, to tmpdir
+    monkeypatch.setenv('TORCH_HOME', tmpdir)
 
     hparams = EvalModelTemplate.get_default_hparams()
 
@@ -373,10 +385,14 @@ def increment_on_load_checkpoint(self, _):
 
     # Other checkpoints can be uncommented if/when resuming mid-epoch is supported
     checkpoints = sorted(glob.glob(os.path.join(trainer.checkpoint_callback.dirpath, '*.ckpt')))
+    if url_ckpt:
+        # transform local paths into url checkpoints
+        ip, port = tmpdir_server
+        checkpoints = [f'http://{ip}:{port}/' + os.path.basename(check) for check in checkpoints]
 
     for check in checkpoints:
         next_model = _new_model()
-        state = torch.load(check)
+        state = pl_load(check)
 
         # Resume training
         trainer_options['max_epochs'] = 2