OfflineIMAP

OfflineIMAP executes a regular operation as part of an assert expression. If PYTHONOPTIMIZE is set, Python skips assert statements, thus OfflineIMAP doesn't execute the regular operation. This has given me quite a headache: deleted messages reappeared on second sync since deletion.

The one location I've found is in offlineimap.folder.IMAP.IMAPFolder.deletemessages_noconvert():

if self.expunge:

    assert(imapobj.expunge()[0] == 'OK')

Other parts of the code might have the same problem. I've verified this bug is still present in the latest release.

From the Python documentation:

Assert statements are a convenient way to insert debugging assertions

 into a program:

/>
 The simple form, "assert expression", is equivalent to
/>
 The current code generator emits no code for an assert statement when 

 optimization is requested at compile time.

if debug:

   if not expression: raise AssertionError