Chapter 1. Getting Started with Django 1.8

In this chapter, we will cover the following topics:

Working with a virtual environment
Creating a project file structure
Handling project dependencies with pip
Making your code compatible with both Python 2.7 and Python 3
Including external dependencies in your project
Configuring settings for development, testing, staging, and production environments
Defining relative paths in the settings
Creating and including local settings
Setting up STATIC_URL dynamically for Subversion users
Setting up STATIC_URL dynamically for Git users
Setting UTF-8 as the default encoding for MySQL configuration
Setting the Subversion ignore property
Creating a Git ignore file
Deleting Python-compiled files
Respecting the import order in Python files
Creating app configuration
Defining overwritable app settings

Introduction

In this chapter, we will see a few good practices when starting a new project with Django 1.8 on Python 2.7 or Python 3. Some of the tricks introduced here are the best ways to deal with the project layout, settings, and configurations. However, for some tricks, you might have to find some alternatives online or in other books about Django. Feel free to evaluate and choose the best bits and pieces for yourself while digging deep into the Django world.

I am assuming that you are already familiar with the basics of Django, Subversion and Git version control, MySQL and PostgreSQL databases, and command-line usage. Also, I am assuming that you are probably using a Unix-based operating system, such as Mac OS X or Linux. It makes more sense to develop with Django on Unix-based platforms as the websites will most likely be published on a Linux server, therefore, you can establish routines that work the same while developing as well as deploying. If you are locally working with Django on Windows, the routines are similar; however, they are not always the same.

Working with a virtual environment

It is very likely that you will develop multiple Django projects on your computer. Some modules such as Python Imaging Library (or Pillow) and MySQLdb, can be installed once and then shared for all projects. Other modules such as Django, third-party Python libraries, and Django apps, will need to be kept isolated from each other. The virtualenv tool is a utility that separates all the Python projects in their own realms. In this recipe, we will see how to use it.

Getting ready

To manage Python packages, you will need pip. It is included in your Python installation if you are using Python 2.7.9 or Python 3.4+. If you are using another version of Python, install pip by executing the installation instructions at http://pip.readthedocs.org/en/stable/installing/. Let's install the shared Python modules Pillow and MySQLdb, and the virtualenv utility, using the following commands:

$ sudo pip install Pillow
$ sudo pip install MySQL-python
$ sudo pip install virtualenv

How to do it…

Once you have your prerequisites installed, create a directory where all your Django projects will be stored, for example, virtualenvs under your home directory. Perform the following steps after creating the directory:

Go to the newly created directory and create a virtual environment that uses the shared system site packages:

$ cd ~/virtualenvs
$ mkdir myproject_env
$ cd myproject_env
$ virtualenv --system-site-packages .
New python executable in ./bin/python
Installing setuptools………….done.
Installing pip……………done.

To use your newly created virtual environment, you need to execute the activation script in your current shell. This can be done with the following command:
```
$ source bin/activate
```
You can also use the following command one for the same (note the space between the dot and bin):
```
$ . bin/activate
```
You will see that the prompt of the command-line tool gets a prefix of the project name, as follows:
```
(myproject_env)$
```
To get out of the virtual environment, type the following command:
```
$ deactivate
```

How it works…

When you create a virtual environment, a few specific directories (bin, build, include, and lib) are created in order to store a copy of the Python installation and some shared Python paths are defined. When the virtual environment is activated, whatever you have installed with pip or easy_install will be put in and used by the site packages of the virtual environment, and not the global site packages of your Python installation.

To install Django 1.8 in your virtual environment, type the following command:

(myproject_env)$ pip install Django==1.8

Creating a project file structure

A consistent file structure for your projects makes you well-organized and more productive. When you have the basic workflow defined, you can get in the business logic quicker and create awesome projects.

Getting ready

If you haven't done this yet, create a virtualenvs directory, where you will keep all your virtual environments (read about this in the Working with a virtual environment recipe). This can be created under your home directory.

Then, create a directory for your project's environment, for example, myproject_env. Start the virtual environment in it. I would suggest adding the commands directory for local bash scripts that are related to the project, the db_backups directory for database dumps, and the project directory for your Django project. Also, install Django in your virtual environment.

How to do it…

Follow these steps in order to create a file structure for your project:

With the virtual environment activated, go to the project directory and start a new Django project as follows:
```
(myproject_env)$ django-admin.py startproject myproject
```
For clarity, we will rename the newly created directory as django-myproject. This is the directory that you will put under version control, therefore, it will have the .git, .svn, or similar directories.
In the django-myproject directory, create a README.md file to describe your project to the new developers. You can also put the pip requirements with the Django version and include other external dependencies (read about this in the Handling project dependencies with pip recipe). Also, this directory will contain your project's Python package named myproject; Django apps (I recommend having an app called utils for different functionalities that are shared throughout the project); a locale directory for your project translations if it is multilingual; a Fabric deployment script named fabfile.py, as suggested in the Creating and using the Fabric deployment script recipe in Chapter 11, Testing and Deployment; and the externals directory for external dependencies that are included in this project if you decide not to use pip requirements.
In your project's Python package, myproject, create the media directory for project uploads, the site_static directory for project-specific static files, the static directory for collected static files, the tmp directory for the upload procedure, and the templates directory for project templates. Also, the myproject directory should contain your project settings, the settings.py and conf directories (read about this in the Configuring settings for development, testing, staging, and production environments recipe), as well as the urls.py URL configuration.
In your site_static directory, create the site directory as a namespace for site-specific static files. Then, separate the separated static files in directories in it. For instance, scss for Sass files (optional), css for the generated minified Cascading Style Sheets, img for styling images and logos, js for JavaScript, and any third-party module combining all types of files such as the tinymce rich-text editor. Besides the site directory, the site_static directory might also contain overwritten static directories of third-party apps, for example, cms overwriting static files from Django CMS. To generate the CSS files from Sass and minify the JavaScript files, you can use the CodeKit or Prepros applications with a graphical user interface.
Put your templates that are separated by the apps in your templates directory. If a template file represents a page (for example, change_item.html or item_list.html), then directly put it in the app's template directory. If the template is included in another template (for example, similar_items.html), put it in the includes subdirectory. Also, your templates directory can contain a directory called utils for globally reusable snippets, such as pagination, language chooser, and others.

How it works…

The whole file structure for a complete project in a virtual environment will look similar to the following:

Handling project dependencies with pip

The pip is the most convenient tool to install and manage Python packages. Besides installing the packages one by one, it is possible to define a list of packages that you want to install and pass it to the tool so that it deals with the list automatically.

You will need to have at least two different instances of your project: the development environment, where you create new features, and the public website environment that is usually called the production environment in a hosted server. Additionally, there might be development environments for other developers. Also, you may have a testing and staging environment in order to test the project locally and in a public website-like situation.

For good maintainability, you should be able to install the required Python modules for development, testing, staging, and production environments. Some of the modules will be shared and some of them will be specific. In this recipe, we will see how to organize the project dependencies and manage them with pip.

Getting ready

Before using this recipe, you need to have pip installed and a virtual environment activated. For more information on how to do this, read the Working with a virtual environment recipe.

How to do it…

Execute the following steps one by one to prepare pip requirements for your Django project:

Let's go to your Django project that you have under version control and create the requirements directory with these text files: base.txt for shared modules, dev.txt for development environment, test.txt for testing environment, staging.txt for staging environment, and prod.txt for production.

Edit base.txt and add the Python modules that are shared in all environments, line by line, for example:

# base.txt
Django==1.8
djangorestframework
-e git://github.com/omab/python-social-auth.git@6b1e301c79#egg=python-social-auth

If the requirements of a specific environment are the same as in the base.txt, add the line including the base.txt in the requirements file of that environment, for example:
```
# prod.txt
-r base.txt
```
If there are specific requirements for an environment, add them as shown in the following:
```
# dev.txt
-r base.txt
django-debug-toolbar
selenium
```
Now, you can run the following command in order to install all the required dependencies for development environment (or analogous command for other environments), as follows:
```
(myproject_env)$ pip install -r requirements/dev.txt
```

How it works…

The preceding command downloads and installs all your project dependencies from requirements/base.txt and requirements/dev.txt in your virtual environment. As you can see, you can specify a version of the module that you need for the Django framework and even directly install from a specific commit at the Git repository for the python-social-auth in our example. In practice, installing from a specific commit would rarely be useful, for instance, only when having third-party dependencies in your project with specific functionality that are not supported in the recent versions anymore.

When you have many dependencies in your project, it is good practice to stick to specific versions of the Python modules as you can then be sure that when you deploy your project or give it to a new developer, the integrity doesn't get broken and all the modules function without conflicts.

If you have already manually installed the project requirements with pip one by one, you can generate the requirements/base.txt file using the following command:

(myproject_env)$ pip freeze > requirements/base.txt

There's more…

If you want to keep things simple and are sure that, for all environments, you will be using the same dependencies, you can use just one file for your requirements named requirements.txt, by definition:

(myproject_env)$ pip freeze > requirements.txt

To install the modules in a new environment simply call the following command:

(myproject_env)$ pip install -r requirements.txt

Note

If you need to install a Python library from other version control system or local path, you can learn more about pip from the official documentation at http://pip-python3.readthedocs.org/en/latest/reference/pip_install.html.

Making your code compatible with both Python 2.7 and Python 3

Since version 1.7, Django can be used with Python 2.7 and Python 3. In this recipe, we will take a look at the operations to make your code compatible with both the Python versions.

Getting ready

When creating a new Django project or upgrading an old existing project, consider following the rules given in this recipe.

How to do it…

Making your code compatible with both Python versions consists of the following steps:

At the top of each module, add from __future__ import unicode_literals and then use usual quotes without a u prefix for Unicode strings and a b prefix for bytestrings.
To ensure that a value is bytestring, use the django.utils.encoding.smart_bytes function. To ensure that a value is Unicode, use the django.utils.encoding.smart_text or django.utils.encoding.force_text function.

For your models, instead of the __unicode__ method, use the __str__ method and add the python_2_unicode_compatible decorator, as follows:

# models.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from django.db import models
from django.utils.translation import ugettext_lazy as _
from django.utils.encoding import \
    python_2_unicode_compatible

@python_2_unicode_compatible
class NewsArticle(models.Model):
    title = models.CharField(_("Title"), max_length=200)
    content = models.TextField(_("Content"))

    def __str__(self):
        return self.title

    class Meta:
        verbose_name = _("News Article")
        verbose_name_plural = _("News Articles")

To iterate through dictionaries, use iteritems(), iterkeys(), and itervalues() from django.utils.six. Take a look at the following:

from django.utils.six import iteritems
d = {"imported": 25, "skipped": 12, "deleted": 3}
for k, v in iteritems(d):
    print("{0}: {1}".format(k, v))

When you capture exceptions, use the as keyword, as follows:

try:
    article = NewsArticle.objects.get(slug="hello-world")
except NewsArticle.DoesNotExist as exc:
    pass
except NewsArticle.MultipleObjectsReturned as exc:
    pass

To check the type of a value, use django.utils.six, as shown in the following:

from django.utils import six
isinstance(val, six.string_types) # previously basestring
isinstance(val, six.text_type) # previously unicode
isinstance(val, bytes) # previously str
isinstance(val, six.integer_types) # previously (int, long)

Instead of xrange, use range from django.utils.six.moves, as follows:

from django.utils.six.moves import range
for i in range(1, 11):
    print(i)

To check whether the current version is Python 2 or Python 3, you can use the following conditions:

from django.utils import six
if six.PY2:
    print("This is Python 2")
if six.PY3:
    print("This is Python 3")

How it works…

All strings in Django projects should be considered as Unicode strings. Only the input of HttpRequest and output of HttpResponse is usually in the UTF-8 encoded bytestring.

Many functions and methods in Python 3 now return the iterators instead of lists, which make the language more efficient. To make the code compatible with both the Python versions, you can use the six library that is bundled in Django.

Read more about writing compatible code in the official Django documentation at https://docs.djangoproject.com/en/1.8/topics/python3/.

Tip

Downloading the example code

You can download the example code files for all Packt books that you have purchased from your account at http://www.packtpub.com. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register in order to have the files e-mailed directly to you.

Including external dependencies in your project

Sometimes, it is better to include external dependencies in your project. This ensures that whenever a developer upgrades third-party modules, all the other developers will receive the upgraded version in the next update from the version control system (Git, Subversion, or others).

Also, it is better to have external dependencies included in your project when the libraries are taken from unofficial sources, that is, somewhere other than Python Package Index (PyPI), or different version control systems.

Getting ready

Start with a virtual environment with a Django project in it.

How to do it…

Execute the following steps one by one:

If you haven't done this already, create an externals directory under your Django project django-myproject directory. Then, create the libs and apps directories under it.
The libs directory is for the Python modules that are required by your project, for example, boto, Requests, Twython, Whoosh, and so on. The apps directory is for third-party Django apps, for example, django-cms, django-haystack, django-storages, and so on.
Tip
I highly recommend that you create the README.txt files in the libs and apps directories, where you mention what each module is for, what the used version or revision is, and where it is taken from.
The directory structure should look something similar to the following:

The next step is to put the external libraries and apps under the Python path so that they are recognized as if they were installed. This can be done by adding the following code in the settings:

# settings.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
import os
import sys

BASE_DIR = os.path.abspath(os.path.join(
    os.path.dirname(__file__), ".."
))

EXTERNAL_LIBS_PATH = os.path.join(
    BASE_DIR, "externals", "libs"
)
EXTERNAL_APPS_PATH = os.path.join(
    BASE_DIR, "externals", "apps"
)
sys.path = ["", EXTERNAL_LIBS_PATH, EXTERNAL_APPS_PATH] + \
    sys.path

How it works…

A module is meant to be under the Python path if you can run Python and import that module. One of the ways to put a module under the Python path is to modify the sys.path variable before importing a module that is in an unusual location. The value of sys.path is a list of directories starting with an empty string for the current directory, followed by the directories in the virtual environment, and finally the globally shared directories of the Python installation. You can see the value of sys.path in the Python shell, as follows:

(myproject_env)$ python
>>> import sys
>>> sys.path

When trying to import a module, Python searches for the module in this list and returns the first result that is found.

Therefore, we first define the BASE_DIR variable, which is the absolute path to one level higher than the settings.py file. Then, we define the EXTERNAL_LIBS_PATH and EXTERNAL_APPS_PATH variables, which are relative to BASE_DIR. Lastly, we modify the sys.path property, adding new paths to the beginning of the list. Note that we also add an empty string as the first path to search, which means that the current directory of any module should always be checked first before checking other Python paths.

Tip

This way of including external libraries doesn't work cross-platform with the Python packages that have C language bindings, for example, lxml. For such dependencies, I would recommend using the pip requirements that were introduced in the Handling project dependencies with pip recipe.

Configuring settings for development, testing, staging, and production environments

As noted earlier, you will be creating new features in the development environment, test them in the testing environment, then put the website to a staging server to let other people to try the new features, and lastly, the website will be deployed to the production server for public access. Each of these environments can have specific settings and you will see how to organize them in this recipe.

Getting ready

In a Django project, we'll create settings for each environment: development, testing, staging, and production.

How to do it…

Follow these steps to configure project settings:

In myproject directory, create a conf Python module with the following files: __init__.py, base.py for shared settings, dev.py for development settings, test.py for testing settings, staging.py for staging settings, and prod.py for production settings.
Put all your shared settings in conf/base.py.
If the settings of an environment are the same as the shared settings, then just import everything from base.py there, as follows:
```
# myproject/conf/prod.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from .base import *
```
Apply the settings that you want to attach or overwrite for your specific environment in the other files, for example, the development environment settings should go to dev.py as shown in the following:
```
# myproject/conf/dev.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from .base import *
EMAIL_BACKEND = \
    "django.core.mail.backends.console.EmailBackend"
```

At the beginning of the myproject/settings.py, import the configurations from one of the environment settings and then additionally attach specific or sensitive configurations such as DATABASES or API keys that shouldn't be under version control, as follows:

# myproject/settings.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from .conf.dev import *

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.mysql",
        "NAME": "myproject",
        "USER": "root",
        "PASSWORD": "root",
    }
}

Create a settings.py.sample file that should contain all the sensitive settings that are necessary for a project to run; however, with empty values set.

How it works…

By default, the Django management commands use the settings from myproject/settings.py. Using the method that is defined in this recipe, we can keep all the required non-sensitive settings for all environments under version control in the conf directory. Whereas, the settings.py file itself would be ignored by version control and will only contain the settings that are necessary for the current development, testing, staging, or production environments.

Defining relative paths in the settings

Django requires you to define different file paths in the settings, such as the root of your media, the root of your static files, the path to templates, the path to translation files, and so on. For each developer of your project, the paths may differ as the virtual environment can be set up anywhere and the user might be working on Mac OS X, Linux, or Windows. Anyway, there is a way to define these paths that are relative to your Django project directory.

Getting ready

To start with, open settings.py.

How to do it…

Modify your path-related settings accordingly instead of hardcoding the paths to your local directories, as follows:

# settings.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
import os

BASE_DIR = os.path.abspath(
    os.path.join(os.path.dirname(__file__), "..")
)

MEDIA_ROOT = os.path.join(BASE_DIR, "myproject", "media")

STATIC_ROOT = os.path.join(BASE_DIR, "myproject", "static")

STATICFILES_DIRS = (
    os.path.join(BASE_DIR, "myproject", "site_static"),
)

TEMPLATE_DIRS = (
    os.path.join(BASE_DIR, "myproject", "templates"),
)

LOCALE_PATHS = (
    os.path.join(BASE_DIR, "locale"),
)

FILE_UPLOAD_TEMP_DIR = os.path.join(
    BASE_DIR, "myproject", "tmp"
)

How it works…

At first, we define BASE_DIR, which is an absolute path to one level higher than the settings.py file. Then, we set all the paths relative to BASE_DIR using the os.path.join function.

Creating and including local settings

Configuration doesn't necessarily need to be complex. If you want to keep things simple, you can work with two settings files: settings.py for common configuration and local_settings.py for sensitive settings that shouldn't be under version control.

Getting ready

Most of the settings for different environments will be shared and saved in version control. However, there will be some settings that are specific to the environment of the project instance, for example, database or e-mail settings. We will put them in the local_settings.py file.

How to do it…

To use local settings in your project, perform the following steps:

At the end of settings.py, add a version of local_settings.py that claims to be in the same directory, as follows:

# settings.py
# … put this at the end of the file …
try:
    execfile(os.path.join(
        os.path.dirname(__file__), "local_settings.py"
    ))
except IOError:
    pass

Create local_settings.py and put your environment-specific settings there, as shown in the following:

# local_settings.py
DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.mysql",
        "NAME": "myproject",
        "USER": "root",
        "PASSWORD": "root",
    }
}

EMAIL_BACKEND = \
    "django.core.mail.backends.console.EmailBackend"

INSTALLED_APPS += (
    "debug_toolbar",
)

How it works…

As you can see, the local settings are not normally imported, they are rather included and executed in the settings.py file itself. This allows you to not only create or overwrite the existing settings, but also adjust the tuples or lists from the settings.py file. For example, we add debug_toolbar to INSTALLED_APPS here in order to be able to debug the SQL queries, template context variables, and so on.

Setting up STATIC_URL dynamically for Subversion users

If you set STATIC_URL to a static value, then each time you update a CSS file, JavaScript file, or image, you will need to clear the browser cache in order to see the changes. There is a trick to work around clearing the browser's cache. It is to have the revision number of the version control system shown in STATIC_URL. Whenever the code is updated, the visitor's browser will force the loading of all-new static files.

This recipe shows how to put a revision number in STATIC_URL for subversion users.

Getting ready

Make sure that your project is under the subversion version control and you have BASE_DIR defined in your settings, as shown in the Defining relative paths in the settings recipe.

Then, create the utils module in your Django project, and also create a file called misc.py there.

How to do it…

The procedure to put the revision number in the STATIC_URL setting consists of the following two steps:

Insert the following content:

# utils/misc.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
import subprocess

def get_media_svn_revision(absolute_path):
    repo_dir = absolute_path
    svn_revision = subprocess.Popen(
        'svn info | grep "Revision" | awk \'{print $2}\'',
        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
        shell=True, cwd=repo_dir, universal_newlines=True)
    rev = svn_revision.communicate()[0].partition('\n')[0]
    return rev

Then, modify the settings.py file and add the following lines:

# settings.py
# … somewhere after BASE_DIR definition …
from utils.misc import get_media_svn_revision
STATIC_URL = "/static/%s/" % get_media_svn_revision(BASE_DIR)

How it works…

The get_media_svn_revision() function takes the absolute_path directory as a parameter and calls the svn info shell command in that directory to find out the current revision. We pass BASE_DIR to the function as we are sure that it is under version control. Then, the revision is parsed, returned, and included in the STATIC_URL definition.

Setting up STATIC_URL dynamically for Git users

If you don't want to refresh the browser cache each time you change your CSS and JavaScript files, or while styling images, you need to set STATIC_URL dynamically with a varying path component. With the dynamically changing URL, whenever the code is updated, the visitor's browser will force loading of all-new uncached static files. In this recipe, we will set a dynamic path for STATIC_URL when you use the Git version control system.

Getting ready

Make sure that your project is under the Git version control and you have BASE_DIR defined in your settings, as shown in the Defining relative paths in the settings recipe.

If you haven't done it yet, create the utils module in your Django project. Also, create a misc.py file there.

How to do it…

The procedure to put the Git timestamp in the STATIC_URL setting consists of the following two steps:

Add the following content to the misc.py file placed in utils/:

# utils/misc.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
import subprocess
from datetime import datetime

def get_git_changeset(absolute_path):
    repo_dir = absolute_path
    git_show = subprocess.Popen(
        'git show --pretty=format:%ct --quiet HEAD',
        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
        shell=True, cwd=repo_dir, universal_newlines=True,
    )
    timestamp = git_show.communicate()[0].partition('\n')[0]
    try:
        timestamp = \
            datetime.utcfromtimestamp(int(timestamp))
    except ValueError:
        return ""
    changeset = timestamp.strftime('%Y%m%d%H%M%S')
    return changeset

Then, import the newly created get_git_changeset() function in the settings and use it for the STATIC_URL path, as follows:

# settings.py
# … somewhere after BASE_DIR definition …
from utils.misc import get_git_changeset
STATIC_URL = "/static/%s/" % get_git_changeset(BASE_DIR)

How it works…

The get_git_changeset() function takes the absolute_path directory as a parameter and calls the git show shell command with the parameters to show the Unix timestamp of the HEAD revision in the directory. As stated in the previous recipe, we pass BASE_DIR to the function as we are sure that it is under version control. The timestamp is parsed; converted to a string consisting of year, month, day, hour, minutes, and seconds; returned; and included in the definition of STATIC_URL.

Setting UTF-8 as the default encoding for MySQL configuration

MySQL is the most popular open source database. In this recipe, I will tell you how to set UTF-8 as the default encoding for it. Note that if you don't set this encoding in the database configuration, you might get into a situation where LATIN1 is used by default with your UTF-8 encoded data. This will lead to database errors whenever symbols such as € are used. Also, this recipe will save you from the difficulties of converting the database data from LATIN1 to UTF-8, especially when you have some tables encoded in LATIN1 and others in UTF-8.

Getting ready

Make sure that the MySQL database management system and the MySQLdb Python module are installed and you are using the MySQL engine in your project's settings.

How to do it…

Open the /etc/mysql/my.cnf MySQL configuration file in your favorite editor and ensure that the following settings are set in the sections: [client], [mysql], and [mysqld], as follows:

# /etc/mysql/my.cnf
[client]
default-character-set = utf8

[mysql]
default-character-set = utf8

[mysqld]
collation-server = utf8_unicode_ci
init-connect = 'SET NAMES utf8'
character-set-server = utf8

If any of the sections don't exist, create them in the file. Then, restart MySQL in your command-line tool, as follows:

$ /etc/init.d/mysql restart

How it works…

Now, whenever you create a new MySQL database, the databases and all their tables will be set in UTF-8 encoding by default.

Don't forget to set this in all computers where your project is developed or published.

Setting the Subversion ignore property

If you are using Subversion for version control, you will need to keep most of the projects in the repository; however, some files and directories should only stay locally and not be tracked.

Getting ready

Make sure that your Django project is under the Subversion version control.

How to do it…

Open your command-line tool and set your default editor as nano, vi, vim or any other that you prefer, as follows:

$ export EDITOR=nano

Tip

If you don't have a preference, I would recommend using nano, which is very intuitive and a simple text editor for the terminal.

Then, go to your project directory and type the following command:

$ svn propedit svn:ignore myproject

This will open a temporary file in the editor, where you need to put the following file and directory patterns for Subversion to ignore:

# Project files and directories
local_settings.py
static
media
tmp

# Byte-compiled / optimized / DLL files
__pycache__
*.py[cod]
*$py.class

# C extensions
*.so

# PyInstaller
*.manifest
*.spec

# Installer logs
pip-log.txt
pip-delete-this-directory.txt

# Unit test / coverage reports
htmlcov
.tox
.coverage
.coverage.*
.cache
nosetests.xml
coverage.xml
*.cover

# Translations
*.pot

# Django stuff:
*.log

# PyBuilder
target

Save the file and exit the editor. For every other Python package in your project, you will need to ignore several files and directories too. Just go to a directory and type the following command:

$ svn propedit svn:ignore .

Then, put this in the temporary file, save it, and close the editor, as follows:

# Byte-compiled / optimized / DLL files
__pycache__
*.py[cod]
*$py.class

# C extensions
*.so

# PyInstaller
*.manifest
*.spec

# Installer logs
pip-log.txt
pip-delete-this-directory.txt

# Unit test / coverage reports
htmlcov
.tox
.coverage
.coverage.*
.cache
nosetests.xml
coverage.xml
*.cover

# Translations
*.pot

# Django stuff:
*.log

# PyBuilder
target

How it works…

In Subversion, you need to define the ignore properties for each directory of your project. Mainly, we don't want to track the Python-compiled files, for instance, *.pyc. We also want to ignore local_settings.py that is specific for each environment, static that replicates collected static files from different apps, media that contains uploaded files and changes together with the database, and tmp that is temporarily used for file uploads.

Tip

If you keep all your settings in a conf Python package as described in the Configuring settings for development, testing, staging, and production environments recipe, add settings.py to the ignored files too.

Creating the Git ignore file

If you are using Git—the most popular distributed version control system—ignoring some files and folders from version control is much easier than with Subversion.

Getting ready

Make sure that your Django project is under the Git version control.

How to do it…

Using your favorite text editor, create a .gitignore file at the root of your Django project and put these files and directories there, as follows:

# .gitignore
# Project files and directories
/myproject/local_settings.py
/myproject/static/
/myproject/tmp/
/myproject/media/

# Byte-compiled / optimized / DLL files
__pycache__/
*.py[cod]
*$py.class

# C extensions
*.so

# PyInstaller
*.manifest
*.spec

# Installer logs
pip-log.txt
pip-delete-this-directory.txt

# Unit test / coverage reports
htmlcov/
.tox/
.coverage
.coverage.*
.cache
nosetests.xml
coverage.xml
*.cover

# Translations
*.pot

# Django stuff:
*.log

# Sphinx documentation
docs/_build/

# PyBuilder
target/

How it works…

The .gitignore file specifies the paths that should intentionally be untracked by the Git version control system. The .gitignore file that we created in this recipe will ignore the Python-compiled files, local settings, collected static files, temporary directory for uploads, and media directory with the uploaded files.

Tip

If you keep all your settings in a conf Python package as described in the Configuring settings for development, testing, staging, and production environments recipe, add settings.py to the ignored files too.

Deleting Python-compiled files

When you run your project for the first time, Python compiles all your *.py code in bytecode-compiled files, *.pyc, which are used later for execution.

Normally, when you change the *.py files, *.pyc is recompiled; however, sometimes when switching branches or moving the directories, you need to clean up the compiled files manually.

Getting ready

Use your favorite editor and edit or create a .bash_profile file in your home directory.

How to do it…

Add this alias at the end of .bash_profile, as follows:

# ~/.bash_profile
alias delpyc="find . -name \"*.pyc\" -delete"

Now, to clean the Python-compiled files, go to your project directory and type the following command in the command line:

$ delpyc

How it works…

At first, we create a Unix alias that searches for the *.pyc files and deletes them in the current directory and its children. The .bash_profile file is executed when you start a new session in the command-line tool.

Respecting the import order in Python files

When you create the Python modules, it is good practice to stay consistent with the structure in the files. This makes it easier for other developers and yourself to read the code. This recipe will show you how to structure your imports.

Getting ready

Create a virtual environment and a Django project in it.

How to do it…

Use the following structure in a Python file that you create. Just after the first line that defines UTF-8 as the default Python file encoding, put the imports categorized in sections, as follows:

# -*- coding: UTF-8 -*-
# System libraries
from __future__ import unicode_literals
import os
import re
from datetime import datetime

# Third-party libraries
import boto
from PIL import Image

# Django modules
from django.db import models
from django.conf import settings

# Django apps
from cms.models import Page

# Current-app modules
from . import app_settings

How it works…

We have five main categories for the imports, as follows:

System libraries for packages in the default installation of Python
Third-party libraries for the additionally installed Python packages
Django modules for different modules from the Django framework
Django apps for third-party and local apps
Current-app modules for relative imports from the current app

There's more…

When coding in Python and Django, use the official style guide for Python code, PEP 8. You can find it at https://www.python.org/dev/peps/pep-0008/.

Creating app configuration

When developing a website with Django, you create one module for the project itself and then, multiple Python modules called applications or apps that combine the different modular functionalities and usually consist of models, views, forms, URL configurations, management commands, migrations, signals, tests, and so on. The Django framework has application registry, where all apps and models are collected and later used for configuration and introspection. Since Django 1.7, meta information about apps can be saved in the AppConfig instance for each used app. Let's create a sample magazine app to take a look at how to use the app configuration there.

Getting ready

Either create your Django app manually or using this command in your virtual environment (learn how to use virtual environments in the Working with a virtual environment recipe), as follows:

(myproject_env)$ django-admin.py startapp magazine

Add some NewsArticle model to models.py, create administration for the model in admin.py, and put "magazine" in INSTALLED_APPS in the settings. If you are not yet familiar with these tasks, study the official Django tutorial at https://docs.djangoproject.com/en/1.8/intro/tutorial01/.

How to do it…

Follow these steps to create and use the app configuration:

First of all, create the apps.py file and put this content in it, as follows:

# magazine/apps.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from django.apps import AppConfig
from django.utils.translation import ugettext_lazy as _

class MagazineAppConfig(AppConfig):
    name = "magazine"
    verbose_name = _("Magazine")

    def ready(self):
        from . import signals

Then, edit the __init__.py file of the app and put the following content:

# magazine/__init__.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
default_app_config = "magazine.apps.MagazineAppConfig"

Lastly, let's create a signals.py file and add some signal handlers there:

# magazine/signals.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from django.db.models.signals import post_save, post_delete
from django.dispatch import receiver
from django.conf import settings
from .models import NewsArticle

@receiver(post_save, sender=NewsArticle)
def news_save_handler(sender, **kwargs):
    if settings.DEBUG:
        print("%s saved." % kwargs['instance'])

@receiver(post_delete, sender=NewsArticle)
def news_delete_handler(sender, **kwargs):
    if settings.DEBUG:
        print("%s deleted." % kwargs['instance'])

How it works…

When you run an HTTP server or invoke a management command, django.setup() is called. It loads the settings, sets up logging, and initializes app registry. The app registry is initialized in three steps, as shown in the following:

Django imports the configurations for each item from INSTALLED_APPS in the settings. These items can point to app names or configuration directly, for example,"magazine" or "magazine.apps.NewsAppConfig".
Django tries to import models.py from each app in INSTALLED_APPS and collect all the models.
Finally, Django runs the ready() method for each app configuration. This method is a correct place to register signal handlers, if you have any. The ready() method is optional.
In our example, the MagazineAppConfig class sets the configuration for the magazine app. The name parameter defines the name of the current app. The verbose_name parameter is used in the Django model administration, where models are presented and grouped by apps. The ready() method imports and activates the signal handlers that, when in DEBUG mode, print in the terminal that a NewsArticle was saved or deleted.

There is more…

After calling django.setup(), you can load the app configurations and models from the registry as follows:

>>> from django.apps import apps as django_apps
>>> magazine_app_config = django_apps.get_app_config("magazine")
>>> magazine_app_config
<MagazineAppConfig: magazine>
>>> magazine_app_config.models_module
<module 'magazine.models' from 'magazine/models.pyc'>
NewsArticle = django_apps.get_model("magazine", "NewsArticle")

You can read more about app configuration in the official Django documentation at https://docs.djangoproject.com/en/1.8/ref/applications/

Defining overwritable app settings

This recipe will show you how to define settings for your app that can be then overwritten in your project's settings.py or local_settings.py file. This is useful especially for reusable apps.

Getting ready

Either create your Django app manually or using the following command:

(myproject_env)$ django-admin.py startapp myapp1

How to do it…

If you just have one or two settings, you can use the following pattern in your models.py file. If the settings are extensive and you want to have them organized better, create an app_settings.py file in the app and put the settings in the following way:

# models.py or app_settings.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from django.conf import settings
from django.utils.translation import ugettext_lazy as _

SETTING1 = getattr(settings, "MYAPP1_SETTING1", u"default value")
MEANING_OF_LIFE = getattr(settings, "MYAPP1_MEANING_OF_LIFE", 42)
STATUS_CHOICES = getattr(settings, "MYAPP1_STATUS_CHOICES", (
    ("draft", _("Draft")),
    ("published", _("Published")),
    ("not_listed", _("Not Listed")),
))

Then, you can use the app settings in models.py, as follows:

# models.py
# -*- coding: UTF-8 -*-
from __future__ import unicode_literals
from django.db import models
from django.utils.translation import ugettext_lazy as _

from .app_settings import STATUS_CHOICES

class NewsArticle(models.Model):
    # …
    status = models.CharField(_("Status"),
        max_length=20, choices=STATUS_CHOICES
    )

If you want to overwrite the STATUS_CHOICES setting for just one project, you simply open settings.py and add the following:

# settings.py
# …
from django.utils.translation import ugettext_lazy as _
MYAPP1_STATUS_CHOICES = (
    ("imported", _("Imported")),
    ("draft", _("Draft")),
    ("published", _("Published")),
    ("not_listed", _("Not Listed")),
    ("expired", _("Expired")),
)

How it works…

The getattr(object, attribute_name[, default_value]) Python function tries to get the attribute_name attribute from object and returns default_value if it is not found. In this case, different settings are tried in order to be taken from the Django project settings module, and if they are not found, the default values are assigned.