Generalise exceptions and fix regression (#125)

* Fix regression for file opening

* Standardize exceptions raised by django-webpack-loader.

Make WebpackError the main exception, and have the rest of the
exceptions inherit form it.

* Create base exception

Author: phala

webpack_loader/exceptions.py

@@ -6,17 +6,31 @@
 )
 
 
-class WebpackError(Exception):
-    pass
+class BaseWebpackLoaderException(Exception):
+    """
+    Base exception for django-webpack-loader.
+    """
 
 
-class WebpackLoaderBadStatsError(Exception):
-    pass
+class WebpackError(BaseWebpackLoaderException):
+    """
+    General webpack loader error.
+    """
 
 
-class WebpackLoaderTimeoutError(Exception):
-    pass
+class WebpackLoaderBadStatsError(BaseWebpackLoaderException):
+    """
+    The stats file does not contain valid data.
+    """
 
 
-class WebpackBundleLookupError(Exception):
-    pass
+class WebpackLoaderTimeoutError(BaseWebpackLoaderException):
+    """
+    The bundle took too long to compile.
+    """
+
+
+class WebpackBundleLookupError(BaseWebpackLoaderException):
+    """
+    The bundle name was invalid.
+    """

webpack_loader/loader.py

@@ -1,5 +1,6 @@
 import json
 import time
+from io import open
 
 from django.conf import settings
 from django.contrib.staticfiles.storage import staticfiles_storage