Pecan uses the Python standard library’s logging module by passing logging configuration options into the logging.config.dictConfig function. The full documentation for the dictConfig() format is the best source of information for logging configuration, but to get you started, this chapter will provide you with a few simple examples.
Sample logging configuration is provided with the quickstart project introduced in Creating Your First Pecan Application:
$ pecan create myapp
The default configuration defines one handler and two loggers.
# myapp/config.py
app = { ... }
server = { ... }
logging = {
'root' : {'level': 'INFO', 'handlers': ['console']},
'loggers': {
'myapp': {'level': 'DEBUG', 'handlers': ['console']}
},
'handlers': {
'console': {
'level': 'DEBUG',
'class': 'logging.StreamHandler',
'formatter': 'simple'
}
},
'formatters': {
'simple': {
'format': ('%(asctime)s %(levelname)-5.5s [%(name)s]'
'[%(threadName)s] %(message)s')
}
}
}
The logger named myapp is reserved for your usage in your Pecan application.
Once you have configured your logging, you can place logging calls in your code. Using the logging framework is very simple.
# myapp/myapp/controllers/root.py
from pecan import expose
import logging
logger = logging.getLogger(__name__)
class RootController(object):
@expose()
def index(self):
if bad_stuff():
logger.error('Uh-oh!')
return dict()
Python’s logging library defines a variety of handlers that assist in writing logs to file. A few interesting ones are:
Using any of them is as simple as defining a new handler in your application’s logging block and assigning it to one of more loggers.
Paste (which is not included with Pecan) includes the TransLogger middleware for logging requests in Apache Combined Log Format. Combined with file-based logging, TransLogger can be used to create an access.log file similar to Apache.
To add this middleware, modify your the setup_app method in your project’s app.py as follows:
# myapp/myapp/app.py
from pecan import make_app
from paste.translogger import TransLogger
def setup_app(config):
# ...
app = make_app(
config.app.root
# ...
)
app = TransLogger(app, setup_console_handler=False)
return app
By default, TransLogger creates a logger named wsgi, so you’ll need to specify a new (file-based) handler for this logger in our Pecan configuration file:
# myapp/config.py
app = { ... }
server = { ... }
logging = {
'loggers': {
# ...
'wsgi': {'level': 'INFO', 'handlers': ['logfile'], 'qualname': 'wsgi'}
},
'handlers': {
# ...
'logfile': {
'class': 'logging.FileHandler',
'filename': '/etc/access.log',
'level': 'INFO',
'formatter': 'messageonly'
}
},
'formatters': {
# ...
'messageonly': {'format': '%(message)s'}
}
}