注意tornado中的日志操作

通过源码可以发现，tornado中也是大量使用了python中的logging模块来处理日志操作。但tornado在处理日志的时候，特别是tornado.options.parse_command_line()时将根日志的级别设置为info，这点需要特别注意！如果在tornado.options.parse_command_line()之前程序对logging的日志级别进行了设置，则很有可能会被tornado进行改写，这点需要特别注意。
通过下面的代码可以很容易就能看出tornado对跟logger的级别进行了调整：

import os
import ssl
import logging
from tornado.httpserver import HTTPServer
from tornado.web import Application, RequestHandler
from tornado.ioloop import IOLoop
import tornado.options
from tornado.options import define, options


LOG = logging.getLogger(__name__)

define("port", default=8000, help="run on the given port", type=int)
class TestHandler(RequestHandler):
    def get(self):
        self.write("Hello, World!\n")

application = Application([
    (r"/", TestHandler),],
    debug = True)

if __name__ == "__main__":
    print "main 1 getEffectiveLevel = ", LOG.getEffectiveLevel()
    print "tornado default log level = "tornado.options.options.logging
    tornado.options.options.logging = "debug"
    tornado.options.parse_command_line()

    print "main getEffectiveLevel = ", LOG.getEffectiveLevel()
    # server = HTTPServer(application,ssl_options={
    #        "certfile": os.path.join(os.path.abspath("."), "cert.pem"),
    #        "keyfile": os.path.join(os.path.abspath("."), "privatekey.pem"),
    #    })
    server = HTTPServer(applicatio)
    server.listen(options.port)
    IOLoop.instance().start()

 对根logger的日志级别进行更改主要是tornado的tornado.options所为，源码如下：

def parse_command_line(self, args=None):
        if args is None:
            args = sys.argv
        remaining = []
        for i in xrange(1, len(args)):
            # All things after the last option are command line arguments
            if not args[i].startswith("-"):
                remaining = args[i:]
                break
            if args[i] == "--":
                remaining = args[i + 1:]
                break
            arg = args[i].lstrip("-")
            name, equals, value = arg.partition("=")
            name = name.replace('-', '_')
            if not name in self:
                print_help()
                raise Error('Unrecognized command line option: %r' % name)
            option = self[name]
            if not equals:
                if option.type == bool:
                    value = "true"
                else:
                    raise Error('Option %r requires a value' % name)
            option.parse(value)
        if self.help:
            print_help()
            sys.exit(0)

        # Set up log level and pretty console logging by default
        if self.logging != 'none':
            logging.getLogger().setLevel(getattr(logging, self.logging.upper()))
            enable_pretty_logging()

        return remaining

# Default options
define("help", type=bool, help="show this help information")
define("logging", default="info",
       help=("Set the Python log level. If 'none', tornado won't touch the "
             "logging configuration."),
       metavar="debug|info|warning|error|none")

 可以看到，tornado.options在parse_command_line的时候，会判断self.logging 是否为none，非none时执行logging.getLogger().setLevel(getattr(logging, self.logging.upper()))，也就是对根logger的level进行设置，在tornado.options被import的时候定义了一个logging，parse_command_line的时候将logging的根级别设置为info。
总之，在tornado应用中，应该特别注意logging级别设置同tornado.options.parse_command_line的先后顺序。