Allow modifying pep images with same name

Currently, 'peps.converters.add_pep_image' does not allow to add an
image that already exists in the database for the same name. As a
consequence images cannot be updated.

This commit modifies 'peps.converters.add_pep_image' to also update
the image db record if the corresponding file has changed as per
'filecmp.cmp'. This requires removing the file prior to the db
update, because the django 'FileField' does not override existing
files.

Alternatives to the ad hoc removal of the file in 'add_pep_image'
include passing a custom 'OverwriteStorage' to the used
'ImageField', see e.g.:

https://code.djangoproject.com/ticket/4339
https://stackoverflow.com/questions/9522759/imagefield-overwrite-image-file-with-same-name

Signed-off-by: Lukas Puehringer <lukas.puehringer@nyu.edu>

Author: Lukas Puehringer

peps/converters.py

@@ -2,6 +2,7 @@
 import datetime
 import re
 import os
+import filecmp
 
 from bs4 import BeautifulSoup
 
@@ -221,8 +222,15 @@ def add_pep_image(artifact_path, pep_number, path):
             FOUND = True
             break
 
-    if not FOUND:
-        image = Image(page=page)
+    # Add image if it does not exist or the new image differs from the existing
+    if not FOUND or not filecmp.cmp(image_path, image.image.path):
+        # If it does not exist we need a new image object ...
+        if not FOUND:
+            image = Image(page=page)
+        # ... otherwise we re-use the existing object from the loop above but
+        # first remove the image file (django does not override)
+        else:
+            os.remove(image.image.path)
 
         with open(image_path, 'rb') as image_obj:
             image.image.save(path, File(image_obj))