Simple slack bot in python
In general this code looks pretty good.  I do have a couple of small pythonism comments:

dict.get() returns None if key not present:

This:

if 'name' in user and user.get('name') == BOT_NAME:


Can simply be this:

if user.get('name') == BOT_NAME:


... since dict.get() will return None if the key is not present and I presume BOT_NAME will never be None.    

Iterating over 0 length item:

This:

if messages and len(messages) &gt; 0:
    for message in messages:


Can simply be this:

if messages:
    for message in messages:


... since the for loop will not have anything to do if the length is zero.

Also, I am not sure what this if is testing for:

if messages:
    for message in messages:


If guarding against None, then it would be more pythonic as:

if messages is not None:
    for message in messages:


And if the check is a surrogate length check, then it isn't necessary at all, and the if could be removed.