pdfstrip.py: make the code simpler and more robust

Instead of relying on the name field of the individual objects, which is
not always defined, find objects by their IDs and delete them using the
"page-local" name which is always defined.

diff --git a/pdfstrip.py b/pdfstrip.py
index 1b287f8..006eefc 100755 (executable)
--- a/pdfstrip.py
+++ b/pdfstrip.py
@@ -34,35 +34,20 @@ logger.addHandler(console_handler)
 logger.propagate = False
 
 
-def resolve_objects_names(pdf, objects_ids):
-    logger.debug("objects_ids %s", objects_ids)
-    objects_names = []
-    for objnum in objects_ids:
-        indirect_object = pdf.findindirect(objnum, 0)
-        if isinstance(indirect_object, PdfIndirect):
-            try:
-                real_object = indirect_object.real_value()
-                if real_object.Name:
-                    objects_names.append(real_object.Name)
-                else:
-                    logger.warning("Object %d has an empty 'Name' attribute", objnum)
-            except AttributeError:
-                logger.warning("Object %d has no 'Name' attribute", objnum)
-        else:
-            logger.warning("Object %d is not a PdfIndirect but a %s",
-                           objnum, type(indirect_object))
-
-    logger.debug("objects_names %s\n", objects_names)
-    return objects_names
-
-
-def strip_objects(pdf, objects_names):
+def strip_objects(pdf, objects_ids):
     for i, page in enumerate(pdf.pages):
         logger.debug("Page %d", i + 1)
+
+        # Map all the objects in the page using the objects id as the key and
+        # the resource name as the value.
+        name_map = {indirect_obj.indirect[0]: name for name, indirect_obj in page.Resources.XObject.items()}
+        logger.debug("name_map: %s", name_map)
+
         logger.debug("Before %s", page.Resources.XObject.keys())
-        for obj in objects_names:
-            if obj in page.Resources.XObject:
-                del page.Resources.XObject[obj]
+
+        for obj in objects_ids:
+            if obj in name_map:
+                del page.Resources.XObject[name_map[obj]]
 
         logger.debug("After  %s\n", page.Resources.XObject.keys())
 
@@ -97,8 +82,7 @@ def main():
 
     pdf_data = PdfReader(args.input_filename)
 
-    objects_names = resolve_objects_names(pdf_data, args.objects_ids)
-    pdf_data = strip_objects(pdf_data, objects_names)
+    pdf_data = strip_objects(pdf_data, args.objects_ids)
 
     PdfWriter().write(args.output_filename, pdf_data)