Web Frameworks: Django

1. Web Frameworks: Django Department of Biomedical Informatics University of Pittsburgh School of Medicine http://www.dbmi.pitt.edu

2. The Purpose of the Lecture Introduce the basic steps for web programming using Django. This is done by walking you though the steps that takes to create an web blog: “jiangblog” “jiangblog” is designed to allow a user to make comments online about some topics such as a presidential debate, and save these comments in a database.

3. Python and SQLite has to be installed before installing django!

4. Download and Install Django • Download Django 1.4.2 from the following website: https://www.djangoproject.com/download/. 2. Install Django: tar xzvf Django-1.4.2.tar.gz cd Django-1.4.2 sudo python setup.py install

5. Create a Django Project Django provides a utility called django-admin.py that can streamline the tasks for you when you create a django project. (Note that I use red color for the terminal output.) xjiang-lp:django xij6$ django-admin.py startproject jiangblog xjiang-lp:django xij6$ ls -l total 0 drwxr-xr-x 4 xij6 PITT\domain users 136 Nov 8 11:28 jiangblog drwxr-xr-x 7 xij6 PITT\domain users 238 Nov 8 11:05 mysite

6. Check What have been Created in jiangblog xjiang-lp:django xij6$ cd jiangblog xjiang-lp:jiangblog xij6$ ls -l total 8 drwxr-xr-x 6 xij6 PITT\domain users 204 Nov 8 11:28 jiangblog -rwxr-xr-x 1 xij6 PITT\domain users 252 Nov 8 11:28 manage.py xjiang-lp:jiangblog xij6$

7. Check What have been Created in jiangblog xjiang-lp:jiangblog xij6$ ls -l jiangblog total 32 -rw-r--r-- 1 xij6 PITT\domain users 0 Nov 8 11:28 __init__.py -rw-r--r-- 1 xij6 PITT\domain users 5221 Nov 8 11:28 settings.py -rw-r--r-- 1 xij6 PITT\domain users 565 Nov 8 11:28 urls.py -rw-r--r-- 1 xij6 PITT\domain users 1140 Nov 8 11:28 wsgi.py

8. The Files Created by Django-Admin.py startproject manage.py: Command-line interface for applications. __init__.py: Specifies to Python that this is a package. urls.py: Global URL configuration (“URLconf”). settings.py: Project-specific configuration wsgi.py: ???

9. The “pure Python” philosophy Note that every file created by the startproject command is Python code with an extension .py Django tries to stay with Python code wherever possible. This certainly reduces the complexity to the framework for a python programmer.

10. Running the Development Server The development server is a server designed for the development phase that runs on your local computer. xjiang-lp:jiangblog xij6$ python ./manage.py runserver Validating models… 0 errors found Django version 1.4.2, using settings 'jiangblog.settings' Development server is running at http://127.0.0.1:8000/ Quit the server with CONTROL-C. Error: [Errno 48] Address already in use

11. Running the Development Server Note that if you want to run your server on a different port, you can specify that on the command line: python ./manage.pyrunserver

12. xjiang-lp:jiangblog xij6$ ./manage.pyrunserver 8080 Validating models... 0 errors found Django version 1.4.2, using settings 'jiangblog.settings' Development server is running at http://127.0.0.1:8080/ Quit the server with CONTROL-C.

14. DBMIAdmins-MacBook-Pro:jiangblog xij6$ ./manage.pystartapppresdebate DBMIAdmins-MacBook-Pro:jiangblog xij6$ ls -l total 8 drwxr-xr-x 10 xij6 PITT\domain users 340 Nov 8 12:32 jiangblog -rwxr-xr-x 1 xij6 PITT\domain users 252 Nov 8 11:28 manage.py drwxr-xr-x 6 xij6 PITT\domain users 204 Nov 8 13:33 presdebate DBMIAdmins-MacBook-Pro:jiangblog xij6$

15. Create an Application within a Project We want to create an application named as “presdebate”, which can be used to collect comments from web users about a presidential debate. ./manage.py startapp presdebate

16. Again, we want to know what files have been created for our application. DBMIAdmins-MacBook-Pro:jiangblog xij6$ ls -l presdebate total 24 -rw-r--r-- 1 xij6 PITT\domain users 0 Nov 8 13:33 __init__.py -rw-r--r-- 1 xij6 PITT\domain users 57 Nov 8 13:33 models.py -rw-r--r-- 1 xij6 PITT\domain users 383 Nov 8 13:33 tests.py -rw-r--r-- 1 xij6 PITT\domain users 26 Nov 8 13:33 views.py DBMIAdmins-MacBook-Pro:jiangblog xij6$

17. The Files Created for our Application “presdebate” __init__.py: Specifies to Python that this is a package models.py: Data models views.py: view functions tests.py: unit tests What is missing? urls.py: The app’s URL configuration (“URLconf”). This is not automatically created.

18. To inform Django that the new app “presdebate” is part of our project, we need to edit settings.py. We need to open the settings.py with an editor and find the INSTALLED_APPS tuple near the bottom, then add our application name (presdebate) as a member of that tuple. In Mac I typically use either textmate or coda2 to do the editing work.

19. NSTALLED_APPS after editing

20. Creating a Data Model We need to create a data model via editing the file called models.py, which is automatically generated for application presdebate. This data model defines the data structures of presdebate. Django provides a variety of fields that map to our application data. In application presdebate, we will use three different field types.

21. Models.py before editing

22. Models.py after editing

23. The newly created class, PresDebate, is a subclass of django.db.models.Model. That’s Django standard base class for data models, which is the core of Django’s powerful ORM. The fields are defined like regular class attributes, with each one being an instance of a particular field class.

24. A CharField is appropriate for short, single lines of text. A TextField type is good for a large chunk of text, such as a large paragraph of comments we may collect from a user. A DateTimeField is represented by a Python datetime.datetime object. For a list of field types provided by Django, refer to the documentation at: https://docs.djangoproject.com/en/dev/ref/models/fields/#field-types

25. Setting Up the Database Using SQLite with the local host, you only need to do two things: • Update the engine. • Specify the name (use full pathname to avoid confusion) of the database that will be created in the settings.py file.

26. DATABASES entry in settings.py before editing

27. “DATABASES”entry in settings.py after editing

28. Setting Up the Database Now we need to tell Django to use the information (the pathname of our database) you’ve given it to connect to the database and set up tables that our application needs. We use the syncdb command of manage.py to do this.

30. Setting Up the Database When the syncdb command is issued, Django looks for a models.py file in each of the INSTALLED_APPS entry. For each model it finds, it creates a database table. Adding a super user is useful, especially when we add the Django’s automatic admin application later.

32. Creating the predebate’s User Interface With Django, a Web page has the following typical components: • A template that defines how it looks, and displays information passed to it. 2. A view function that performs the core logic for a request, fetch the information to be displayed from a database, and store new information entered by a users to the database.

33. Creating the Predebate’s User Interface 3. A URL pattern that matches an incoming request with the corresponding view. We will build our application according to the following order: • Build a template. • Design an Url Pattern. • Develop the view function.

34. Creating a Django Template We will introduce two constructs of django’s templating language: • A variable tag that is delimited by pairs of curly braces: {{ … }}. A variable tag displays the contents of the object within the braces, which can be pure data or callables. Inside a variable tag, you can use Python-style dot-notation to access attributes of the tag variables.

35. Creating a Django Template • A block tag that is delimited by curly braces and percent symbols : {% … %}. A block tag is used to embed logic such as loops and conditions into a django html template.

36. A Preliminary Template Created for presdebate Application

37. Creating a Django Template Save the HTML template code shown in the previous slide into a directory called templates inside the application folder, which we need to create. So the path to the template we just created is: /users/xij6/django/jiangblog/presdebate/templates/mytemplate.html Note that the name of the template is arbitrary, but the name of the templates directory is mandatory.

38. Creating a URL Pattern The pathnames of an URL in a users’ browsers are mapped to various parts of an applicaton. The IP address will be mapped to an Internet host (server), and the port number will be mapped to a port on the server. Once the message arrives at the Internet host, the serve will match the remainder of the URL to the corresponding project. Then the remainder of the URL (with the project name excluded) will be passed to the project url configuration file.

39. Creating a URL Pattern In our case in which we use a local host as the server, the type of request and the remainder of the URL (with the IP and port number excluded) will be passed to a django project URLconf (jiangblog/urls.py). We therefore need to edit the URLconf so that when a valid pattern (regular expression) matches to the remainder of the URL received, the request will be further passed to the next receiver, which is the application URLconf we shell create later.

40. jiangblog/urls.py before editing

41. jiangblog/urls.py after editing

42. Creating a URL Pattern The patterns() function takes as input a tuple (URL regular expression, destination). The destination is either a view function that is called for URLs that match the pattern, or it’s a call to another URLconf file via include() function. When include() is used, the current URL path head is removed and the remainder of the path is passed to the another URLconf file.

43. Creating a URL Pattern For example, for http://localhost:8080/presdebate/xxx/yyy/zzz, the xxx/yyy/zzz will be passed to presdebate/urls.py as specified by include (“presdebate.urls”), by excluding the matching regex presdebate/

44. Creating a URL Pattern The added line in the urlpattens entry of the project URLconf says that we are catching requests that begin with presdebate/ and passing them on to the presdebate/urls.py. Recall that the presdebatedoes not contain a urls.py, thus we need to create this file from scratch.

45. presdebate/urls.py

46. Creating a View Function-Create a Fake View First The purpose of creating a fake view is to test quickly whether we’ve done so fast are correct. To do this, we need to edit the jiangblog/presdebate/view.py file.

47. jiangblog/presdebate/view.py before editing

48. jiangblog/presdebate/view.py after editing