Pony fails with mysql on Python 2.6

[thedrow]

See this import error: https://travis-ci.org/maxtepkeev/architect/jobs/38495030

[amalashkevich]

Could you try to launch python2.6 and then do the import:

    from _mysql import string_literal

If the import fails then you need to check what is wrong with MySQLdb installation

[thedrow]

Nothing is wrong. Breakage was introduced with 0.5.4.
https://travis-ci.org/maxtepkeev/architect/jobs/38506193

[amalashkevich]

Trying to figure out where is the problem. Could you launch python2.6 in your testing environment and do the import

    from _mysql import string_literal

What is the result of such import?

[socketpair]

Thanks for not supporting Centos 6 / RedHATE 6. These distros should die with very outdated Python 2.6.

[maxtepkeev]

Hi!

I found the cause of the problem, now we just have to figure out how to properly fix it. This has nothing to do with Python 2.6, this problem exists in all Python versions and all Pony versions starting from 0.5.4.

In my code I use

from pymysql import install_as_MySQLdb
install_as_MySQLdb()

which I believe is a perfectly valid way to use pymysql instead of mysqldb. Now, the thing is that in Pony you have the following inside orm/dbproviders/mysql.py:

try:
    import MySQLdb as mysql_module
except ImportError as e:
    try:
        import pymysql as mysql_module
    except ImportError:
        raise ImportError('No module named MySQLdb or pymysql found')
    else:
        import pymysql.converters as mysql_converters
        from pymysql.constants import FIELD_TYPE, FLAG, CLIENT
        mysql_converters.encoders[buffer] = lambda val: mysql_converters.escape_str(str(val))
        mysql_converters.encoders[timedelta] = lambda val: mysql_converters.escape_str(timedelta2str(val))
        mysql_module_name = 'pymysql'
else:
    import MySQLdb.converters as mysql_converters
    from MySQLdb.constants import FIELD_TYPE, FLAG, CLIENT
    mysql_module_name = 'MySQLdb'
    from _mysql import string_literal

What happens here is that because I already installed pymysql as mysqldb using the install_as_MySQLdb() pony thinks that mysqldb is installed in the system and the ImportError exception is not raised which causes the else block to execute which leads to this error.

To fix this we can eliminate the else block and move all it's code to the try block like this:

try:
    import MySQLdb as mysql_module
    import MySQLdb.converters as mysql_converters
    from MySQLdb.constants import FIELD_TYPE, FLAG, CLIENT
    mysql_module_name = 'MySQLdb'
    from _mysql import string_literal
except ImportError as e:
    try:
        import pymysql as mysql_module
    except ImportError:
        raise ImportError('No module named MySQLdb or pymysql found')
    else:
        import pymysql.converters as mysql_converters
        from pymysql.constants import FIELD_TYPE, FLAG, CLIENT
        mysql_converters.encoders[buffer] = lambda val: mysql_converters.escape_str(str(val))
        mysql_converters.encoders[timedelta] = lambda val: mysql_converters.escape_str(timedelta2str(val))
        mysql_module_name = 'pymysql'

That will fix the error and make everybody happy. If you agree I can make a pull request or you can inject this fix by yourself.

What do you think ?

[kozlovsky]

Thanks for the patch! I fixed the Pony code according to your suggestion, it will be part of the upcoming release PonyORM 0.6.2

[maxtepkeev]

Awesome, thanks!