Improve error message for %logstop

[takluyver]

If %logstop is called when logging is not active, it throws a traceback with a fairly unhelpful AttributeError: 'NoneType' object has no attribute 'close'. We should catch this error and display a one-line message like "Logging hadn't been started."

[bernardpaulus]

Hello!

By taking a peek in the current code (commit 088eb7d), it can solved by (in IPython/core/logger.py) :

def logstop(self):
    """Fully stop logging and close log file.

    In order to start logging again, a new logstart() call needs to be
    made, possibly (though not necessarily) with a new filename, mode and
    other options."""

    if self.logfile is not None:
        self.logfile.close()
        self.logfile = None
    self.log_active = False

and the diff

--- a/IPython/core/logger.py
+++ b/IPython/core/logger.py
@@ -206,8 +206,9 @@ which already exists. But you must first start the logging p
         made, possibly (though not necessarily) with a new filename, mode and
         other options."""

-        self.logfile.close()
-        self.logfile = None
+        if self.logfile is not None:
+            self.logfile.close()
+            self.logfile = None
         self.log_active = False

     # For backwards compatibility, in case anyone was using this.

I'm not familiar with git yet, so either you commit this directly, or you wait I read http://progit.org/book/ ;)

[takluyver]

Thanks, Bernard. I think we should also display a brief error message when it's called from a magic command. That's best added to magic_logstop:

https://github.com/ipython/ipython/blob/master/IPython/core/magic.py#L1194

A brief rundown of using github:

Click the fork button to copy the repo to your own account. Then on your computer:

git clone https://github.com/bernardpaulus/ipython.git
cd ipython
git checkout -b logstop-error   # last bit is the branch name
# Change files as desired
git commit -a
git push origin logstop-error

Finally, back on github, find the branch you changed, and click the 'Pull request' button to submit the changes. We've got a more detailed explanation of the workflow in the docs: http://ipython.org/ipython-doc/stable/development/gitwash/index.html

[bernardpaulus]

fixed in #834

I however put the print statement in logger.py since other functions inside it behave like that (switch_log() for instance https://github.com/ipython/ipython/blob/master/IPython/core/logger.py#L127 )

Thanks for your explanations!

[takluyver]

Thanks - closing this issue.