feed: Don't pop from extra_headers while iterating over it

Avoid:

  Traceback (most recent call last):
    ...
      for k,v in extra_headers.items():
    File "/.../Python-3.5.0a1/Lib/_collections_abc.py", line 503, in __iter__
      for key in self._mapping:
    File "/.../Python-3.5.0a1/Lib/collections/__init__.py", line 112, in __iter__
      yield curr.key
  AttributeError: 'NoneType' object has no attribute 'key'

from continuing to iterate on items() after popping a key.  This
worked in Python 3.4 but no longer works in Python 3.5.  In any case,
mutating an object while iterating over it is always a bit
questionable, so rephrase to find the keys in one pass, and then
remove them after the iteration completes.

Reported-by: Raniere Silva <raniere@ime.unicamp.br>
Signed-off-by: W. Trevor King <wking@tremily.us>

diff --git a/rss2email/feed.py b/rss2email/feed.py
index ec5c4f683741fe3b8d4c10c3ebea15dfbab941e2..f2750efdc296b0375a70935dfee556d92b709876 100644 (file)
--- a/rss2email/feed.py
+++ b/rss2email/feed.py
@@ -470,9 +470,10 @@ class Feed (object):
                 ('X-RSS-URL', self._get_entry_link(entry)),
                 ('X-RSS-TAGS', self._get_entry_tags(entry)),
                 ))
-        for k,v in extra_headers.items():  # remove empty tags, etc.
-            if v is None:
-                extra_headers.pop(k)
+        # remove empty tags, etc.
+        keys = {k for k, v in extra_headers.items() if v is None}
+        for key in keys:
+            extra_headers.pop(key)
         if self.bonus_header:
             for header in self.bonus_header.splitlines():
                 if ':' in header: