Web2py logging

To get logging to work in web2py, add the following code to the end of db.py (the code is taken, with few modifications, from here).

import logging, logging.handlers

class GAEHandler(logging.Handler):

"""

    Logging handler for GAE DataStore

"""

    def emit(self, record):

        from google.appengine.ext import db

        class Log(db.Model):

            name = db.StringProperty()

            level = db.StringProperty()

            module = db.StringProperty()

            func_name = db.StringProperty()

            line_no = db.IntegerProperty()

            thread = db.IntegerProperty()

            thread_name = db.StringProperty()

            process = db.IntegerProperty()

            message = db.StringProperty(multiline=True)

            args = db.StringProperty(multiline=True)

            date = db.DateTimeProperty(auto_now_add=True)

        log = Log()

        log.name = record.name

        log.level = record.levelname

        log.module = record.module

        log.func_name = record.funcName

        log.line_no = record.lineno

        log.thread = record.thread

        log.thread_name = record.threadName

        log.process = record.process

        log.message = record.msg

        log.args = str(record.args)

        log.put()

def get_configured_logger(name):

    logger = logging.getLogger(name)

    if (len(logger.handlers) == 0):

        # This logger has no handlers, so we can assume it hasn't yet been configured

        # (Configure logger)

        # Create default handler

        if request.env.web2py_runtime_gae:

            # Create GAEHandler

            handler = GAEHandler()

        else:

            # Create RotatingFileHandler

            import os

            formatter="%(asctime)s %(levelname)s %(process)s %(thread)s %(funcName)s():%(lineno)d %(message)s"

            handler = logging.handlers.RotatingFileHandler(os.path.join(request.folder,'private/app.log'),maxBytes=1024,backupCount=2)

            handler.setFormatter(logging.Formatter(formatter))

        handler.setLevel(logging.DEBUG)

        logger.addHandler(handler)

        logger.setLevel(logging.DEBUG)

        # Test entry:

        logger.debug(name + ' logger created')

    else:

        # Test entry:

        logger.debug(name + ' already exists')

    return logger

# Assign application logger to a global var

logger = get_configured_logger(request.application)

Once this is done, you can log things via:

    logger.info("The price was %r" % request.vars.price)

or (another example):

    logger.info("An integer %r or string %r variable" % (16, "may"))

You have various levels of logging; I recommend using:

debug: use rarely. Not well supported on appengine.
info: use for information you want to log (e.g. to help debug, or simply to follow progress of each request).
warning: something unusual happened, but not really an error in your code.
error: an error in your code occurred.

I particularly like to use the %r format for logs, since it is able to convert any Python object to something printable.

The logs are left in /private/ directories of apps, such as (in Mac):

/Applications/web2py.app/Contents/Resources/applications/your_application_name/private

On Appengine, the logs are added to the regular logs.

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