Exception handler in ConnectionPool.__init__ does not close all open connections and raises IndexError

When an error happens while initializing ConnectionPool (for me it was OperationalError: Too many connections), the error handling code does not close all open connections and raises an IndexError

Steps to Reproduce

not tested

1. change ConnectionPool._init_

   index a18d81a..cf59d82 100644

   --- a/mariadb/connectionpool.py

   +++ b/mariadb/connectionpool.py

   @@ -108,6 +108,8 @@ class ConnectionPool(object):

   # fill connection pool

   for i in range(0, self._pool_args["size"]):

   try:

   + if i == 5:

   + raise mariadb.Error("ONLY TESTING")

   connection = mariadb.Connection(**self._conn_args)

   except mariadb.Error:

   # if an error occurred, close all connections

2. Initialize ConnectionPool {{c = ConnectionPool(<parameters>)}

Expected result

• Connections 0…4 get closed
• mariadb.Error raised

Actual result

• Only every second connection closed.
• Raises IndexError: list index out of range

Suggested Fix

Not tested.

Delete connections in reverse order:

diff --git a/mariadb/connectionpool.py b/mariadb/connectionpool.py

index a18d81a..1a69cba 100644

--- a/mariadb/connectionpool.py

+++ b/mariadb/connectionpool.py

@@ -112,7 +112,7 @@ class ConnectionPool(object):

                     except mariadb.Error:

                         # if an error occurred, close all connections

                         # and raise exception

-                        for j in range(0, len(self._connections_free)):

+                        for j in reversed(range(len(self._connections_free))):

                             try:

                                 self._connections_free[j].close()

                             except mariadb.Error: