Question

I’m learning tornado now, and I think it’s an excellent framework.
Everything is well until I separate some methods from main.py.

For example:

In the main.py which is my server startup program. I use tornado.options.define to define some properties like this:

define("port", default=8888, help="run on the given port", type=int)
define("mysql_host", default="127.0.0.1:3306", help="blog database host")
define("mysql_database", default="forum", help="database name")
define("mysql_user", default="root", help="database user")
define("mysql_password", default="passwd", help="database password")

And there is a BaseHandler in it:

class BaseHandler(tornado.web.RequestHandler):
@property
def db(self):
    return self.application.db

def get_current_user(self):
    return self.get_secure_cookie("username")

And in another file, such as topic.py, every handler in the topic.py will extend BaseHandler in main.py, so I import BaseHandler like this:

from main import BaseHandler

Then the problem happen when I startup my program:

Traceback (most recent call last):
  File "/Users/abc/money/main.py", line 85, in <module>
    define("port", default=8888, help="run on the given port", type=int)
  File "/Library/Python/2.7/site-packages/tornado-2.2-py2.7.egg/tornado/options.py", line 93, in define
options[name].file_name)
tornado.options.Error: ('Option %r already defined in %s', 'port', '/Users/suyejun/Dropbox/money/main.py')

How can I avoid this kind of problem? Or is there another way to write the code?

Answer 1

You need to move BaseHandler to a different file that main.py. The problem you are having is that you are effectively loading up the code for main.py twice. Once when you start your application and again when you import the code into topic.py.

I would recommend making a seperate file called something like ‘pagemanager.py’ and put any shared classes, functions, code there. Then you are import those into both main.py and topic.py without causing issues with the code that is specific to the initialization of Tornado.