Question

I want to read mails from a mbox file and do some action based on that. I don’t want to write/modify the mbox file but it will be modified by another process (Mostly adding new mails).

I am reading this documentation. http://docs.python.org/library/mailbox.html#mailbox.mbox

But I don’t understand the following

1. Should I call lock() before reading the mail? (I am not writing to
   the file)
2. Is there anyway I can get a callback when other process
   (thunderbird) modifies the file?
3. Is the changes in the file reflected in the mbox object? I mean, after I create the mbox object, if a new mail is added to the file, will I access the message using the object? Or should I create a new object again?

PS: I am not allowed to install any plugins of thunderbird:(

Answer 1

1. No need to call Mailbox.lock() when you don’t modify the mbox. A quote from the documentation of Mailbox.lock() (emphasis my own):

   You should always lock the mailbox before making any modifications to
   its contents.

2. Notification on file changes is out of the scope of the mailbox module. On Linux systems you can use pyinotify to get this functionality.

3. This is also answered in the documentation:

   The default Mailbox iterator iterates over message representations, not keys as the
   default dictionary iterator does. Moreover, modification of a mailbox during iteration
   is safe and well-defined. Messages added to the mailbox after an iterator is created
   will not be seen by the iterator. Messages removed from the mailbox before the
   iterator yields them will be silently skipped, though using a key from an iterator
   may result in > a KeyError exception if the corresponding message is subsequently
   removed.

   In short, you need to create a new Mailbox instance, after the mbox file has changed.