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 cement2.core import foundation, hook
from cement2.core.exc import CementRuntimeError

try:
    app = foundation.CementApp('helloworld')
    app.setup()
    app.run()
    print('Hello World')
except CementRuntimeError as e:
    # do something with e
    pass
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 that is where cement_on_close_hook() is 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 cement_on_close_hook(). For example:

from cement2.core import hook

@hook.register()
def cement_on_close_hook(app):
    # do something when app.close() is called
    pass