Executing “SELECT … WHERE … IN …” using MySQLdb

Question

I\'m having a problem executing some SQL from within Python, despite similar SQL working fine from the mysql command-line.

The table looks like this:

Answer 1

Improving on João's and satru's code, I suggest creating a cursor mixin that can be used to build a cursor with an execute that accepts nested iterables and handles them correctly. A better name would be nice, though... For Python3, use str instead of basestring.

from MySQLdb.cursors import Cursor

class BetterExecuteMixin(object):
    """
    This mixin class provides an implementation of the execute method
    that properly handles sequence arguments for use with IN tests.
    Examples:
    execute('SELECT * FROM foo WHERE id IN (%s) AND type=%s', ([1,2,3], 'bar'))
    # Notice that when the sequence is the only argument, you still need
    # a surrounding tuple:
    execute('SELECT * FROM foo WHERE id IN (%s)', ([1,2,3],))
    """

    def execute(self, query, args=None):
        if args is not None:
            try:
                iter(args)
            except TypeError:
                args = (args,)
            else:
                if isinstance(args, basestring):
                    args = (args,)
            real_params = []
            placeholders = []
            for arg in args:
                # sequences that we treat as a single argument
                if isinstance(arg, basestring):
                    real_params.append(arg)
                    placeholders.append('%s')
                    continue
                try:
                    real_params.extend(arg)
                    placeholders.append(','.join(['%s']*len(arg)))
                except TypeError:
                    real_params.append(arg)
                    placeholders.append('%s')
            args = real_params
            query = query % tuple(placeholders)
        return super(BetterExecuteMixin, self).execute(query, args)

class BetterCursor(BetterExecuteMixin, Cursor):
    pass

This can then be used as follows (and it's still backwards compatible!):

import MySQLdb
conn = MySQLdb.connect(user='user', passwd='pass', db='dbname', host='host',
                       cursorclass=BetterCursor)
cursor = conn.cursor()
cursor.execute('SELECT * FROM foo WHERE id IN (%s) AND type=%s', ([1,2,3], 'bar'))
cursor.execute('SELECT * FROM foo WHERE id IN (%s)', ([1,2,3],))
cursor.execute('SELECT * FROM foo WHERE type IN (%s)', (['bar', 'moo'],))
cursor.execute('SELECT * FROM foo WHERE type=%s', 'bar')
cursor.execute('SELECT * FROM foo WHERE type=%s', ('bar',))