pool_pre_ping not a valid kwarg for create_engine for MySQL

I am on the most up-to-date SQLAlchemy (1.1.12), and trying to use the pool_pre_ping=True in the create_engine() function. Attempting to use pool_pre_ping results in an error, that pool_pre_ping is not a valid keyword argument.

Here is a test that anyone can run to re-create the problem. Instructions for needed dependencies, my version of MySQL, and my driver are in the comments at the top of the code. You will need to replace "mysql://...." with the credentials for your own database.

'''
Setup instructions for Python 3.4 or 3.5 (will probably work for any version of 3):
pip install sqlalchemy=='1.1.12'
pip install mysqlclient #database driver; necessary for MySQL & sqlalchemy for Python 3 

I have MySQL version 5.6.33 on Ubuntu 14.04
'''
from sqlalchemy import create_engine #import create_engine

engine = create_engine("mysql://username:password@localhost:port/dbname?charset=utf8mb4", pool_pre_ping=True) #attempt to create engine

'''
FULL STACK TRACE ERROR: 
Traceback (most recent call last):
  File "test.py", line 10, in <module>
    engine = create_engine("mysql://username:password@localhost:port/dbname?charset=utf8mb4", pool_pre_ping=True)
  File "/home/hclent/anaconda3/lib/python3.5/site-packages/sqlalchemy/engine/__init__.py", line 387, in create_engine
    return strategy.create(*args, **kwargs)
  File "/home/hclent/anaconda3/lib/python3.5/site-packages/sqlalchemy/engine/strategies.py", line 160, in create
    engineclass.__name__))
TypeError: Invalid argument(s) 'pool_pre_ping' sent to create_engine(), using configuration MySQLDialect_mysqldb/QueuePool/Engine.  Please check that the keyword arguments are appropriate for this combination of components.
'''

I have attached this code in a .py file as well. Running it will show the error just as I have documented it (but make sure to follow the setup instructions!)

Other comments:

If I navigate to the directory where SQLALchemy files are .../lib/python3.5/site-packages/sqlalchemy, and try: grep -r pool_pre_ping * | less There are no results, suggesting that pool_pre_ping is not actually valid for the stable release of sqlalchemy. I also checked the __init__.py in sqlalchemy/engine, where the create_engine( ) function lives, and it does not mention pool_pre_ping anywhere.

According to this documentation, create_engine(..., pool_pre_ping=True) should not fail. Since I am using MySQL and need a reliable connection pool for many users, disabling the pool as suggested in Issue 3919 and spelled out here is not a good alternative.

That being said, the release of 1.2.0b1 seems to have a bugfix that would allow me to do create_engine.pool_pre_ping( ... ). Does this mean I should be using an unstable version of SQLAlchemy?

In summary, given the documentation, the fact I'm using SQLAlchemy 1.1.12, I believe that there is a bug here.

Please let me know if I am missing anything in my Issue (I believe I properly followed the guidelines) and if there's any way I can help contribute :)

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