Checking ipywidgets is installed for ensure tqdm working (#2417)

* Adding importing ipywidgets before importing tqdm.auto to make sure ipywidgets is installed.

* Updated CHANGELOG.md

* Updated ipywidgets importing checks to @awaelchli comments.

Co-authored-by: William Falcon <waf2107@columbia.edu>

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ## [unreleased] - YYYY-MM-DD
 
+### Fixed
+
+- Fixed crashing or wrong displaying progressbar because of missing ipywidgets ([#2417](https://github.com/PyTorchLightning/pytorch-lightning/pull/2417))
+
 ### Added
 
 
@@ -20,7 +24,6 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
-
 ## [0.8.3] - 2020-06-29
 
 ### Fixed

pytorch_lightning/callbacks/progress.py

@@ -5,9 +5,16 @@
 Use or override one of the progress bar callbacks.
 
 """
+import importlib
 import sys
 
-from tqdm.auto import tqdm
+
+# check if ipywidgets is installed before importing tqdm.auto
+# to ensure it won't fail and a progress bar is displayed
+if importlib.util.find_spec('ipywidgets') is not None:
+    from tqdm.auto import tqdm
+else:
+    from tqdm import tqdm
 
 from pytorch_lightning.callbacks import Callback
 

pytorch_lightning/trainer/lr_finder.py

@@ -1,15 +1,23 @@
 """
 Trainer Learning Rate Finder
 """
+import os
+import importlib
 from abc import ABC, abstractmethod
 from typing import Optional, Sequence, Tuple, List, Union
 
 import numpy as np
 import torch
 from torch.optim.lr_scheduler import _LRScheduler
 from torch.utils.data import DataLoader
-from tqdm.auto import tqdm
-import os
+
+# check if ipywidgets is installed before importing tqdm.auto
+# to ensure it won't fail and a progress bar is displayed
+if importlib.util.find_spec('ipywidgets') is not None:
+    from tqdm.auto import tqdm
+else:
+    from tqdm import tqdm
+
 
 from pytorch_lightning.core.lightning import LightningModule
 from pytorch_lightning.callbacks import Callback