Merge pull request #164 from inferno-pytorch/gradient_callback

add gradient logging callback

inferno/trainers/callbacks/__init__.py

@@ -1,9 +1,10 @@
-__all__ = ['CallbackEngine','Callback', 'Console','essentials','scheduling']
+__all__ = ['CallbackEngine', 'Callback', 'Console', 'essentials', 'scheduling', 'gradients']
 
 from .base import CallbackEngine, Callback
 from .console import Console
 from . import essentials
 from . import scheduling
+from . import gradients
 
 try:
     from .tqdm import TQDMProgressBar

inferno/trainers/callbacks/gradients.py

@@ -0,0 +1,49 @@
+from ...utils.train_utils import Frequency
+from ...utils.exceptions import assert_, FrequencyValueError
+from .base import Callback
+
+
+class LogOutputGradients(Callback):
+    """Logs the gradient of the network output"""
+
+    def __init__(self, frequency):
+        super(LogOutputGradients, self).__init__()
+        self.log_every = frequency
+        self.registered = False
+        self.hook_handle = None
+
+    @property
+    def log_every(self):
+        return self._log_every
+
+    @log_every.setter
+    def log_every(self, value):
+        self._log_every = Frequency(value, 'iterations')
+        assert_(self.log_every.is_consistent,
+                "Log frequency is not consistent.",
+                FrequencyValueError)
+
+    def add_hook(self):
+        def hook(module, grad_input, grad_output):
+            if self.log_every.match(iteration_count=self.trainer.iteration_count,
+                                    epoch_count=self.trainer.epoch_count,
+                                    persistent=True, match_zero=True):
+                self.trainer.update_state('output_gradient', grad_output[0].detach().cpu())
+
+        self.hook_handle = self.trainer.model.register_backward_hook(hook)
+
+    def begin_of_fit(self, **kwargs):
+        self._trainer.logger.observe_state("output_gradient",
+                                           observe_while='training')
+        self.add_hook()
+
+    def begin_of_save(self, **_):
+        # remove hook from model, because you can't pickle it.
+        if self.hook_handle is not None:
+            self.hook_handle.remove()
+            self.hook_handle = None
+
+
+    def end_of_save(self, **_):
+        # add hook after model save
+        self.add_hook()