使用带Python的Google App Engine无法看到调试打印语句

Question

I am new to both Google App Engine and Python. When things go wrong I'd like to see variable values and such, but print statements don't seem to be output anywhere. I would have expected them to appear in the same window where I started dev_appserver, but the only time I can see them is if a server error is imminent, then they appear in the output as I'd expect, right before the server error. Otherwise I don't see them.

I'm sure I'm missing something very fundamental... it seems everyone else can see their print statements just fine. I have tried using the logger functionality, but best I can tell it is intended for deployed apps. At any rate I can't see any output from those either. A simple example:

class PageHandler(BaseHandler):
def get(self): 
    // the page renders just fine, but no print statement to be found
    print "rendering the page!"        
    self.render("page.html")

Am I just looking in the wrong spot for the print output? Do I need to be doing something to redirect output before printing? Very confused why the print statements work only when an error is about to occur.

Answer 1

print outputs to standard output ( sys.stdout ) whose destination on a web app is always iffy. Rather, use the logging module...:

import logging
...
logging.info('rendering the page')

and you'll be able to see all messages in the logs.