pylab.lt website

Website for Python workshops internal needs.

Contacts

Website: pylab.lt

Mailing list: https://groups.google.com/d/forum/python-dirbtuves

Development environment

You need Ubuntu 14.04 or greater. In Ubuntu terminal execute these commands:

$ sudo apt-get install python-dev python3-dev
$ sudo apt-get install postgresql
$ sudo apt-get install python-pip   # Python package management system
$ sudo pip install virtualenv       # A tool to create isolated Python environments
$ sudo apt-get install libpq.dev    # info: https://packages.debian.org/jessie/libpq-dev
$ sudo apt-get install g++          # C++ compiler for some Python modules
$ sudo -u postgres psql
# create role <unix_username>;
# alter role <unix_username> with superuser;
# alter role <unix_username> with login;
$ createdb pylab          # Creates Postgresql database with name ``pylab``
$ make                    # Downloads and configures python packages
$ bin/django migrate      # Creates tables in the database
$ make testall            # Checks if everything works properly
$ make run                # Runs localserver

Project structure

Principles

We use Separation of concerns, Command-query separation and Multilayered architecture principles to organize code structure.

Separation of concerns

This is principle, when code is organized into modules by business logic. Sometimes people name their modules something like utils or helpers. These names should be avoided, unless they live in a small scoped Django app, for example accounts.utils or accounts/helpers would be good naming.

In other words, SoC principle tells us to separate our code by business logic, not by code type or something like that.

Command-query separation

This principle tells us to separate commands and queries to separate modules. In our case we separate commands and queries to single module called services.

It means, that our models.py should be used only for model definitions, no more logic should be put into models.py, unless this is directly related with model itself.

All business logic should go to services. For Django apps with larger scope, services should be a package with modules in it, for apps with smaller scope, services can be a module.

Multilayered architecture

This principle explains, that it is not enough to have code organized by business logic, we also need need layered architecture to be able to manage dependencies between those modules more flexibly.

In Django case, we have these layers:

1. Data access layer - basically this is model definitions in models.py.
2. Business layer - services, helpers, forms, utilities and so on.
3. Application layer - views, admin, sometimes helpers and forms.
4. Presentation layer - urls, templates.

Multilayered architecture have one important rule: each layer can access only same or lower layer.

Structure

At the top level project has these folders:

• config - contains project build configuration.
• pylab - this is the whole source code of our project.
• scripts - various utility scripts.
• var - files that are created or generated automatically, these files should not be kept under version control.
• parts - this is similar to var but used by Buildout, usually we store static assets automatically downloaded by hexagonit.recipe.download recipe or other artifacts created by other Buildout recipes.

Dependencies between apps

As mentioned above, pylab folder contains the source code and it contains list of Django apps. Only locale ad settings are not apps. locale contains translation strings and settings - Django settings.

Also there is two special apps, core and website.

Usually most of the code can be easily refactored when project grows, but Django models are not that easy to refactor. Each refactoring that touches models required database migrations and database migrations are something that you have to be careful with.

To avoid refactoring issues, we keep all project data access logic in single Django app called core. Also this helps us to better manage dependencies between apps. Since core contains data access logic which is lowest layer according to multilayered architecture, this means, that is is very likely, that most of the code will depend on this app. So since core tend to be referenced by many other modules and apps, we keep core lean.

website app is another special case and it belongs to application and presentation layers. This means that no other apps can website depend on website, but website should depend on all other apps. In other words, website works like top level app with purpose to connect all components in order to assemble whole project.

The visualisation of app interdependencies could looks like this:

+------------+
| website    |
+------------+
      |
      v   ,------+
+------------+   |
| other apps |<--+
+------------+
      |
      v
+------------+
| core       |
+------------+