Application Cleanup

The concept of ‘cleanup’ after application run time is nothing new. What happens during ‘cleanup’ all depends on the application. This might mean cleaning up temporary files, removing session data, or removing a PID (Process ID) file.

To allow for application cleanup not only within your program, but also external plugins and extensions, there is the app.close() function that must be called after app.run() and after program execution.

For example:

from cement.core import foundation
from cement.core.exc import CementRuntimeError

app = foundation.CementApp('helloworld')

try:
    app.setup()
    app.run()
finally:
    app.close()

You will note that we put app.run() within a ‘try’ block, and app.close() in a ‘finally’ block. The important thing to note is that we put app.close() within a ‘finally’ block so that regardless of whether an exception is encountered or not, we always run app.close(). The primary purpose of app.close() is that is where the ‘pre_close’ and ‘post_close’ hooks are run, allowing extensions/plugins/etc to cleanup after the program runs.

Running Cleanup Code

Any extension, or plugin, or even the application itself that has ‘cleanup’ code can do so within the ‘pre_close’ or ‘post_close’ hooks. For example:

from cement.core import hook

def my_cleanup(app):
    # do something when app.close() is called
    pass

hook.register('pre_close', my_cleanup)