I am new to python and even newer to tornado/momoko. I am struggling with an example from momoko’s website. I have the database.cfg file configured with my settings.
#!/usr/bin/env python
import tornado.httpserver
import tornado.ioloop
import tornado.options
import tornado.web
from tornado import gen
import momoko
import settings
class BaseHandler(tornado.web.RequestHandler):
@property
def db(self):
return self.application.db
class OverviewHandler(BaseHandler):
def get(self):
self.write('''
<ul>
<li><a href="/query">A single query</a></li>
<li><a href="/batch">A batch of queries</a></li>
<li><a href="/chain">A chain of queries</a></li>
<li><a href="/multi_query">Multiple queries executed with gen.Task</a></li>
<li><a href="/callback_and_wait">Multiple queries executed with gen.Callback and gen.Wait</a></li>
</ul>
''')
self.finish()
class SingleQueryHandler(BaseHandler):
@tornado.web.asynchronous
@gen.engine
def get(self):
# One simple query
cursor = yield gen.Task(self.db.execute, 'SELECT 42, 12, %s, 11;', (25,))
self.write('Query results: %s' % cursor.fetchall())
self.finish()
class BatchQueryHandler(BaseHandler):
@tornado.web.asynchronous
@gen.engine
def get(self):
# These queries are executed all at once and therefore they need to be
# stored in an dictionary so you know where the resulting cursors
# come from, because they won't arrive in the same order.
cursors = yield gen.Task(self.db.batch, {
'query1': ['SELECT 42, 12, %s, %s;', (23, 56)],
'query2': 'SELECT 1, 2, 3, 4, 5;',
'query3': 'SELECT 465767, 4567, 3454;'
})
for key, cursor in cursors.items():
self.write('Query results: %s = %s<br>' % (key, cursor.fetchall()))
self.finish()
class QueryChainHandler(BaseHandler):
@tornado.web.asynchronous
@gen.engine
def get(self):
# Execute a list of queries in the order you specified
cursors = yield gen.Task(self.db.chain, (
['SELECT 42, 12, %s, 11;', (23,)],
'SELECT 1, 2, 3, 4, 5;'
))
for cursor in cursors:
self.write('Query results: %s<br>' % cursor.fetchall())
self.finish()
class MultiQueryHandler(BaseHandler):
@tornado.web.asynchronous
@gen.engine
def get(self):
cursor1, cursor2, cursor3 = yield [
gen.Task(self.db.execute, 'SELECT 42, 12, %s, 11;', (25,)),
gen.Task(self.db.execute, 'SELECT 42, 12, %s, %s;', (23, 56)),
gen.Task(self.db.execute, 'SELECT 465767, 4567, 3454;')
]
self.write('Query 1 results: %s<br>' % cursor1.fetchall())
self.write('Query 2 results: %s<br>' % cursor2.fetchall())
self.write('Query 3 results: %s' % cursor3.fetchall())
self.finish()
class CallbackWaitHandler(BaseHandler):
@tornado.web.asynchronous
@gen.engine
def get(self):
self.db.execute('SELECT 42, 12, %s, 11;', (25,),
callback=(yield gen.Callback('q1')))
self.db.execute('SELECT 42, 12, %s, %s;', (23, 56),
callback=(yield gen.Callback('q2')))
self.db.execute('SELECT 465767, 4567, 3454;',
callback=(yield gen.Callback('q3')))
cursor1 = yield gen.Wait('q1')
cursor2 = yield gen.Wait('q2')
cursor3 = yield gen.Wait('q3')
self.write('Query 1 results: %s<br>' % cursor1.fetchall())
self.write('Query 2 results: %s<br>' % cursor2.fetchall())
self.write('Query 3 results: %s' % cursor3.fetchall())
self.finish()
def main():
try:
tornado.options.parse_command_line()
application = tornado.web.Application([
(r'/', OverviewHandler),
(r'/query', SingleQueryHandler),
(r'/batch', BatchQueryHandler),
(r'/chain', QueryChainHandler),
(r'/multi_query', MultiQueryHandler),
(r'/callback_and_wait', CallbackWaitHandler),
], debug=True)
application.db = momoko.AsyncClient({
'host': settings.host,
'port': settings.port,
'database': settings.database,
'user': settings.user,
'password': settings.password,
'min_conn': settings.min_conn,
'max_conn': settings.max_conn,
'cleanup_timeout': settings.cleanup_timeout
})
http_server = tornado.httpserver.HTTPServer(application)
http_server.listen(8888)
tornado.ioloop.IOLoop.instance().start() # the problem lies here, I believe
except KeyboardInterrupt:
print('Exit')
if __name__ == '__main__':
main()
When I run the script, I get the error:
[E 121023 15:31:07 ioloop:337] Exception in I/O handler for fd 6
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/tornado/ioloop.py", line 327, in start
self._handlers[fd](fd, events)
File "/usr/local/lib/python2.7/dist-packages/momoko/pools.py", line 313, in _io_callback
state = self._conn.poll()
OperationalError: asynchronous connection failed
I can connect to the webserver. If I type in “http://localhost:8888/” I see 5 links (ie “A single query”, “A batch of queries”, etc). When I click on one, however, I get:
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 1021, in _stack_context_handle_exception
raise_exc_info((type, value, traceback))
File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 265, in _nested
if exit(*exc):
File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 161, in __exit__
return self.exception_handler(type, value, traceback)
File "/usr/local/lib/python2.7/dist-packages/tornado/gen.py", line 114, in handle_exception
return runner.handle_exception(typ, value, tb)
File "/usr/local/lib/python2.7/dist-packages/tornado/gen.py", line 388, in handle_exception
self.run()
File "/usr/local/lib/python2.7/dist-packages/tornado/gen.py", line 343, in run
yielded = self.gen.throw(*exc_info)
File "/home/desktop-admin/Desktop/eclipse/workspace/jive_backend/test.py", line 35, in get
cursor = yield gen.Task(self.db.execute, 'SELECT 42, 12, %s, 11;', (25,))
File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 258, in _nested
yield vars
File "/usr/local/lib/python2.7/dist-packages/tornado/stack_context.py", line 228, in wrapped
callback(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/momoko/pools.py", line 313, in _io_callback
state = self._conn.poll()
OperationalError: asynchronous connection failed
Momokois wrapper forpsycopg2, not formysql.With mysql try to use something from list on this page:
If you are using postgresql – try to connect to it in synchronous way first.