Update GradientDescentTrainer to automatically create directory for serialization_dir (#4940)

* Automatically create serialization_dir when GradientDescent is instantiated

* Update CHANGELOG

* Update CHANGELOG.md

Co-authored-by: Evan Pete Walsh <[email protected]>

* Move to unreleased

* Update CHANGELOG.md

* Update trainer.py

* Fix

* Update CHANGELOG.md

* Fix whitespace

Co-authored-by: Evan Pete Walsh <[email protected]>

Author: Makoto Hiramatsu

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Added `tokenizer_kwargs` and `transformer_kwargs` arguments to `PretrainedTransformerBackbone`
 
+### Changed
+
+- GradientDescentTrainer makes `serialization_dir` when it's instantiated, if it doesn't exist.
+
 ### Fixed
 
 - `common.util.sanitize` now handles sets.

allennlp/training/trainer.py

@@ -81,6 +81,9 @@ def __init__(
         self._rank = local_rank
         self._primary = self._rank == 0
         self._world_size = world_size
+        # Ensure serialization directory exists.
+        if serialization_dir is not None:
+            os.makedirs(serialization_dir, exist_ok=True)
 
     def train(self) -> Dict[str, Any]:
         """