How do I write to the console in Google App Engine?

Question

Often when I am coding I just like to print little things (mostly the current value of variables) out to console. I don't see anything like this for Google App Engine, although I note that the Google App Engine Launcher does have a Log terminal. Is there any way to write to said Terminal, or to some other terminal, using Google App Engine?

Chris Calo · Accepted Answer · 2015-09-26T18:40:59.233

68

You'll want to use the Python's standard logging module.

import logging

logging.info("hello")
logging.debug("hi") # this won't show up by default

To see calls to logging.debug() in the GoogleAppEngineLauncher Logs console, you have to first add the flag --dev_appserver_log_level=debug to your app. However, beware that you're going to see a lot of debug noise from the App Engine SDK itself. The full set of levels are:

debug
info
warning
error
critical

You can add the flag by double clicking the app and then dropping it into the Extra Flags field.

edited Sep 26 '15 at 18:40

answered Mar 12 '12 at 00:23

Chris Calo

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This was the most helpful response. It deserves notice – AturSams Jun 25 '12 at 00:54
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According to [this more recent answer](http://stackoverflow.com/a/22467787/346561), you should use the extra flag `--log_level=debug` instead of `--debug`. – Jesse Webb Dec 17 '14 at 17:30
I am trying to set my log level to warning to hide the INFO noise but its not working. Any Ideas? – Jay Kyburz Jul 08 '15 at 01:35
turns out --dev_appserver_log_level=warning is the correct setting – Jay Kyburz Jul 08 '15 at 01:40

score 32 · Answer 2 · edited Feb 02 '15 at 12:45

32

See https://cloud.google.com/appengine/docs/python/requests#Python_Logging
and http://docs.python.org/library/logging.html

You probably want to use something like:

logging.debug("value of my var is %s", str(var))

edited Feb 02 '15 at 12:45

Mathias Bynens

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answered Apr 07 '09 at 20:23

vartec

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How can i do the same in java? – Manjoor Jun 26 '10 at 12:33
14

You'll most likely want to use logging.info() instead of logging.debug() because the default logging level in the GoogleAppEngineLauncher Logs console is such that you won't see any calls to logging.debug(). – Chris Calo Mar 12 '12 at 00:26
The first link to the Logging for Python GAE is broken. It should be updated to https://cloud.google.com/appengine/docs/python/requests#Python_Logging – Jesse Webb Dec 17 '14 at 17:21

score 9 · Answer 3 · answered Dec 07 '10 at 18:54

@Manjoor

You can do the same thing in java.

import java.util.logging.Logger;
// ...

public class MyServlet extends HttpServlet {
    private static final Logger log = Logger.getLogger(MyServlet.class.getName());

    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {

        log.info("An informational message.");

        log.warning("A warning message.");

        log.severe("An error message.");
    }
}

See "Logging" in http://code.google.com/appengine/docs/java/runtime.html

score 4 · Answer 4 · answered Mar 17 '14 at 23:53

If you're using a more recent version of the Python Development Server (releases > 1.7.6, or Mar 2013 and later), these seem to be the right steps to use:

Include the following in your script,

import logging logging.debug("something I want to log")
And per this docs page, set a flag by going to Edit > Application Settings > Launch Settings > Extra Command Line Flags, and adding,

--log_level=debug

score 2 · Answer 5 · answered Apr 07 '09 at 23:49

2

You should also give FirePython a look. It allows you to get server log messages in firebug.

http://appengine-cookbook.appspot.com/recipe/firepython-logger-console-inside-firebug/

answered Apr 07 '09 at 23:49

Sam

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score 1 · Answer 6 · answered Nov 22 '13 at 18:37

1

Hello I'm using the version 1.8.6 of GoogleAppEngineLauncher, you can use a flag to set the messages log level you want to see, for example for debug messages:

--dev_appserver_log_level debug

Use it instead of --debug (see @Christopher answer).

answered Nov 22 '13 at 18:37

Abimael

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score 1 · Answer 7 · answered Aug 30 '11 at 05:46

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Check out my online Python interpreter running on Google App Engine on my website, Learn Python. It might be what you're looking for. Just use print repr(variable) on things you want to look at, and execute as many times as you want.

answered Aug 30 '11 at 05:46

Ron Reiter

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score 0 · Answer 8 · answered Jul 24 '13 at 19:10

0

GAE will capture standard error and print it to the console or to a log.

print >> sys.stderr, "Something to log."

answered Jul 24 '13 at 19:10

bugloaf

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score 0 · Answer 9 · answered Sep 24 '13 at 16:30

Use log.setLevel(Level.ALL) to see messages

The default message filtering level seems to be 'error'. I didn't see any useful log messages until I used the setLevel() method to make the .info and .warning messages visible.

Text printed to System.out wasn't showing up either. It seems to be interpreted as log.info() level messaages.

score 0 · Answer 10 · answered Jan 06 '16 at 10:36

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I hope i am answering the question. The logging messages print to the AppEngine log rather than the terminal.

You can launch it by clicking on the logs button of the AppEngine Launcher

answered Jan 06 '16 at 10:36

user5751790

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clickbait · Answer 11 · 2018-07-31T03:10:11.533

0

Using the logging module is good practice, but it's not required.

You can just do plain-old print()s to write to the Google App Engine Log Console.

edited Jul 31 '18 at 03:10

answered Jul 30 '18 at 19:05

clickbait

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How do I write to the console in Google App Engine?

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