Type Hints for Lightning Core (Lightning-AI#946)

* first pass for LightningModule typehints

* fix return types

* add missing types

* add type annotations to grads.py

* add type annotations to hooks.py

* add type annotation to memory.py

* proper docstring quotation marks

* add type annotations to saving.py

* fix cyclic import problem

* fix cyclic import problem

* add missing whitespace

* finish type hints for load_from_ methods

* docs: prepare_data does not return anything

* fix auto types in docs

* revert typehint for trainer in hook

* remove unnecessary return docs

* some fixes for memory docs

* revert typing for args kwargs

* added all missing None return types

* remove unused import

* add more details to dict/list return types

* fix line too long

* optimize imports

* linted

* Revert "linted"

This reverts commit 8555961.

* remove whitespace

* update

* update

* update

* update

* update

* changelog

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>
Co-authored-by: William Falcon <waf2107@columbia.edu>

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Added
 
+- Added type hints to `pytorch_lightning.core` ([#946](https://github.com/PyTorchLightning/pytorch-lightning/pull/946))
 - Added support for IterableDataset in validation and testing ([#1104](https://github.com/PyTorchLightning/pytorch-lightning/pull/1104))
 
 ### Changed

pytorch_lightning/core/grads.py

@@ -1,13 +1,14 @@
 """
 Module to describe gradients
 """
+from typing import Dict
 
 from torch import nn
 
 
 class GradInformation(nn.Module):
 
-    def grad_norm(self, norm_type):
+    def grad_norm(self, norm_type: float) -> Dict[str, int]:
         results = {}
         total_norm = 0
         for name, p in self.named_parameters():

pytorch_lightning/core/hooks.py

@@ -14,10 +14,11 @@
 3. Add the correct place in the :py:mod:`pytorch_lightning.models.trainer` where it should be called.
 
 """
-
+from typing import Any
 
 import torch
-
+from torch import Tensor
+from torch.optim.optimizer import Optimizer
 
 try:
     from apex import amp
@@ -36,48 +37,45 @@ def on_sanity_check_start(self):
         :return:
         """
 
-    def on_train_start(self):
+    def on_train_start(self) -> None:
         """Called at the beginning of training before sanity check
-        :return:
         """
         # do something at the start of training
 
-    def on_train_end(self):
+    def on_train_end(self) -> None:
         """
         Called at the end of training before logger experiment is closed
-        :return:
         """
         # do something at the end of training
 
-    def on_batch_start(self, batch):
+    def on_batch_start(self, batch: Any) -> None:
         """Called in the training loop before anything happens for that batch.
 
         :param batch:
-        :return:
         """
         # do something when the batch starts
 
-    def on_batch_end(self):
+    def on_batch_end(self) -> None:
         """Called in the training loop after the batch."""
         # do something when the batch ends
 
-    def on_epoch_start(self):
+    def on_epoch_start(self) -> None:
         """Called in the training loop at the very beginning of the epoch."""
         # do something when the epoch starts
 
-    def on_epoch_end(self):
+    def on_epoch_end(self) -> None:
         """Called in the training loop at the very end of the epoch."""
         # do something when the epoch ends
 
-    def on_pre_performance_check(self):
+    def on_pre_performance_check(self) -> None:
         """Called at the very beginning of the validation loop."""
         # do something before validation starts
 
-    def on_post_performance_check(self):
+    def on_post_performance_check(self) -> None:
         """Called at the very end of the validation loop."""
         # do something before validation end
 
-    def on_before_zero_grad(self, optimizer):
+    def on_before_zero_grad(self, optimizer: Optimizer) -> None:
         """Called after optimizer.step() and before optimizer.zero_grad()
 
         Called in the training loop after taking an optimizer step and before zeroing grads.
@@ -89,17 +87,13 @@ def on_before_zero_grad(self, optimizer):
             model.on_before_zero_grad(optimizer) # < ---- called here
             optimizer.zero_grad
 
-        :param optimizer:
-        :return:
+        :param optimizer: The optimizer for which grads should be zeroed.
         """
         # do something with the optimizer or inspect it.
 
-    def on_after_backward(self):
-        """Called after loss.backward() and before optimizers do anything.
-
-        :return:
+    def on_after_backward(self) -> None:
+        """Called in the training loop after loss.backward() and before optimizers do anything.
 
-        Called in the training loop after model.backward()
         This is the ideal place to inspect or log gradient information
 
         .. code-block:: python
@@ -116,14 +110,13 @@ def on_after_backward(self):
 
         """
 
-    def backward(self, trainer, loss, optimizer, optimizer_idx):
+    def backward(self, trainer, loss: Tensor, optimizer: Optimizer, optimizer_idx: int) -> None:
         """Override backward with your own implementation if you need to
 
         :param trainer: Pointer to the trainer
         :param loss: Loss is already scaled by accumulated grads
         :param optimizer: Current optimizer being used
         :param optimizer_idx: Index of the current optimizer being used
-        :return:
 
         Called to perform backward step.
         Feel free to override as needed.