datafolklabs/cement

Application Framework for Python

BJ Dierkes

@derks

awesome

Dela Anthonio

@delaanthonio

When I try to get a value using app.config.get('section', 'value') and the value doesn't exist, I get a configparser.NoOptionError, yet I cannot handle this exception since I'm not sure which module it's declared in. I tried searching for it in the cement source code but I couldn't find the module which declares the error. I would like to know how to catch this error or if I should just set all the default app.config values before I parse a config file.

BJ Dierkes

@derks

import configparser
try:
    pass
except configparser.NoOptionError as e:
    pass

should work in theory

Dela Anthonio

@delaanthonio

I see. I didn't notice that configparser is in the Python standard library.

BJ Dierkes

@derks

It is, yeah

In generate, a lot of the interfaces/handlers in Cement are built on top of other libraries. Cement core has zero dependencies so most things are in Python Standard Library (Logging, ConfigParser, Argparse, etc)

AkhIL

@akhilman

@derks, take a look how plugins implemented in https://github.com/click-contrib/click-plugins and https://docs.openstack.org/developer/stevedore/. They are uses entry points from setuptools to automaticaly descover plugins

BJ Dierkes

@derks

@akhilman early versions of cement used entry points but there were issues with it, and I think Cement 2 was the first release that dropped it

maybe things have changed since then though

Craig Schlegelmilch

@cschlegelmilch

Hello, I was wondering if I could ask for some design advice. My project is essentially split into two version where there is a “regular” version and a “lite” version where the lite version is a subset of functionality of the regular. However, this doesn’t mean that the suite of commands differs, it means that the commands themselves do more in the regular version than the lite version. Is there a “Cementy” way of structuring this? I see that there is a plugin infrastructure that sort of checks off all of the boxes but is really does seem built for adding additional functionality, not overridding core functionality. Is that a valid description? Or am I just SOL and need to manage this myself?

BJ Dierkes

@derks

The commands are the same… but the arguments differ? What exactly differs?

and could you give an example?

Craig Schlegelmilch

@cschlegelmilch

For sake of argument, lets assume that commands are exactly the same. The difference is the behaviour/implemenation of the commands differs between the versions of the app

Essentially, I want to replace the functionality of an entire controller

BJ Dierkes

@derks

Literally replace (like two complete different controllers in code), or extend (build off of the lite version to add functionality)?

Craig Schlegelmilch

@cschlegelmilch

The later. If I was I talking in OO terms, I would want to inherit from the original controller and override the methods that define the commands

BJ Dierkes

@derks

Yeah, basically… this is maybe what I would look at… you have LiteController.some_command .. and some_command() would call _actual_code_of_some_command() … AdvancedController would inherit LiteController, but override _actual_code_of_some_command() ….

the interface to the end user is the same, but the logic differs

Craig Schlegelmilch

@cschlegelmilch

Am I able to package that up as a plugin? Or is that just the wrong question?

BJ Dierkes

@derks

you could also have some_command() call _some_command_lite() and _some_command_advanced() … and the AdvancedController would only override _some_command_advanced() (which would preserve the lite versions code, but do more things also)

You can definitely do a plugin. What I would try is, the plugin would import and subclass yourapp.whatever.controllers.LiteController … and then int he plugin’s load() function you would app.handler.register(AdvancedController, force=True) which forces it to register overtop of the LiteController (of the same label)

BJ Dierkes

@derks

assumes that LiteController.Meta.label and AdvancedController.Meta.label are the same, because it provides the same functionality

Craig Schlegelmilch

@cschlegelmilch

Ah. There’s the magic sauce (force=true). That’s what I was looking for. OK, cool. This makes sense.

BJ Dierkes

@derks

Awesome

Craig Schlegelmilch

@cschlegelmilch

Just as a sanity check, this isn’t going to break into a million pieces once v3 is out is it?

(I’m now starting to roadmap the migration to Python 3 and Cement 3)

BJ Dierkes

@derks

No no… most of the core api will be pretty well intact (loading plugins, etc). Especially if you build off of cement.ext.ext_argparse.ArgparseController

Craig Schlegelmilch

@cschlegelmilch

Which I am. Good stuff.

BJ Dierkes

@derks

Major design change will be things like from cement.core.foundation import CementApp will be from cement import App …

Simplifying usage

Craig Schlegelmilch

@cschlegelmilch

Nice. You know when its going to drop?

I promise not to hold you to it

BJ Dierkes

@derks

from cement.ext.ext_argparse import ArgparseController, expose … will be from cement import Controller, ex … things like that.

I’ve made a few of the major changes already… I’m actually focussig mainly on revamping the site and documentation

I’m hoping for later this year

I’m rewriting SphinxDoc to Markdown… it’s mostly just tedious work right now… then I will button up the major design changes I wanted to roll out

p3j4p5

@p3j4p5

Hi everyone,
I hope this is the right place to ask.
I've started working on a project that is using the Cement framework and I would like to ask a few things.
We are using a plugin that takes a number of config options.
Those options get set in the expected place in: /etc/<project_name>/<project_name>.conf
The question is, what is the most elegant way to retrieve the config options inside a plugin?
I know it is possible to do something like: self.app.config.get('section', 'option') in the _setup function of the plugin but is there a way retrieve that information without invoking app?
Didn't have much luck when reading the docs, so I would appreciate if someone could point me to the right place.
Thanks,
Paul

BJ Dierkes

@derks

what is the reason for not wanting to invoke app?

if it is simply because it is annoying to call self.app.config.get (understandable) you could create a shortcut like using get_section_dict

like self.config = self.app.config.get_section_dict(‘my_plugin’) … then just use self.config[‘my_key’] through out your plugin

@p3j4p5 ^

p3j4p5

@p3j4p5

Thanks,
The main reason is that app is only available in the `_seti

The main reason is that app is only available in the _setup method.

BJ Dierkes

@derks

actually, app is passed to the _setup() method … because that is called when the plugin is instantiated during app.setup(). You should set self.app = app in _setup() .. or if you subclass from cement.core.handler.CementHandler just make sure you super() in _setup() and it does that

afte app.setup() you can access self.app anywhere in the plugin class

p3j4p5

@p3j4p5

okay, thank you @derks! I will try that

zero-signal

@zero-signal

Hi! Just getting to grips with the framework although have hit a stumbling block. Using cement 2.10.2 and following the BOSS app creation documentation. Created an app although when I run it it doesnt seem to load the example.py plugin module. Have not modified the BOSS app in anyway. Any thoughts? Can post debug output if that is any use?

Checked for tickets relating to this on both cement and BOSS issue trackers but cannot see anything obvious

Thanks in advance

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