Introduction to Django and installation

B.Krishnakumar

Architecture

virtual environment

• It is a way for you to have multiple versions of python on your machine without them clashing with each other, each version can be considered as a development environment and you can have different versions of python libraries and modules all isolated from one another

How to create Virtual Environment?�

• Step – 1
• Open your terminal and create a directory to store all your virtual environments, using the command mkdir (mkdir environment)
• Now go inside the directory using the command CD which stands for call Directory, CD Environments (cd environment)
• Step 2
• use a module named virtualenv to create isolated virtual environments.
• So, first install this module by the following command,
• pip install virtualenv
• To verify a successful installation run this
• virtualenv –versionNow
• Next, create a virtual environment named myenv.

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How to create Virtual Environment?

• How to create Virtual Environment if you have two different versions of Python installed in your machine?
• To create a Virtual Environment for Python 2.x do the following
• virtualenv myenv
• For a Python 3 virtual environment type –
• python3 -m venv myenvI
• if you only have Python 3 on your machine do the following
• virtualenv myenv
• This will also work 🡪 python -m venv myenv

• To add modules and packages in our Environment, we need to activate it first.

​

• myenv\Scripts\activate.bat
• test\Scripts\activate.bat

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Installing Django

• proceed to Install Django.
• pip install Django
• to know the version of Django installed in your system execute this is terminal.
• django-admin --version

Creating and Running a Django Project�

• django-admin startproject mysite
• mysite/
• manage.py
• mysite/
• __init__.py
• settings.py
• urls.py
• wsgi.py

Running A Django Project

• python manage.py runserver

​

• open your preferred browser and go to http://127.0.0.1:8000/

Creating A Django App�

• python manage.py startapp my_app
• Open your preferred text editor and open the settings.py file and scroll to the INSTALLED_APPS section.
• INSTALLED_APPS =

[ 'django.contrib.admin',

'django.contrib.auth',

'django.contrib.contenttypes', 'django.contrib.sessions',

'django.contrib.messages',

'django.contrib.staticfiles',

'my_app' ]

Creating Web App

• views.py

from django.http import HttpResponse

def index(request):

return HttpResponse('Hello, World !')

• urls.py

from django.contrib import admin

from django.urls import path

# imported views

from my_app import views

urlpatterns = [

path('admin/', admin.site.urls),

# configured the url

path('',views.index, name="homepage")

]

• python manage.py runserver
• visit http://127.0.0.1:8000/

URLconfs and Loose Coupling

• loose coupling is a software-development approach that values the importance of making pieces interchangeable.
• If two pieces of code are loosely coupled, then changes made to one of the pieces will have

little or no effect on the other.

​

• In a Django web application, the URL definitions and the view functions they call are loosely coupled
• that is, the decision of what the URL should be for a given function, and the implementation of the function itself, reside in two separate places. This lets you switch out one piece without affecting the other.

• If we wanted to change the URL for the application – say, to move it from /time/ to /current-time/ – we could make a quick change to the URLconf, without having to worry about the view itself.
• if we wanted to change the view function – altering its logic somehow – we could do that without affecting the URL to which the function is bound.

• if we wanted to expose the current-date functionality at several URLs
• url(r’^time/$’, current_datetime),
• url(r’^another-time-page/$’, current_datetime),

Dynamic URLs

• In our current_datetime view, the contents of the page – the current date/time – were dynamic, but the URL (/time/) was static.

​

• Let’s create a third view that displays the current date and time offset by a certain number of hours.
• The goal is to craft a site in such a way that the page /time/plus/1/ displays the date/time one hour into the future,
• The page /time/plus/2/ displays the date/time two hours into the future,
• the page /time/plus/3/ displays the date/time three hours into the future, and so on.

urlpatterns = patterns(’’,

url(r’^time/$’, current_datetime),

url(r’^time/plus/1/$’, one_hour_ahead),

url (r’^time/plus/2/$’, two_hours_ahead),

url(r’^time/plus/3/$’, three_hours_ahead),

url (r’^time/plus/4/$’, four_hours_ahead),

)

• url(r’^time/plus/\d+/$’, hours_ahead),

​

• url(r’^time/plus/\d{1,2}/$’, hours_ahead),

def hours_ahead(request, offset):

try:

offset = int(offset)

except ValueError:

raise Http404()

dt = datetime.datetime.now() + datetime.timedelta(hours=offset)

html = "<html><body>In %s hour(s), it will be %s.</body></html>" % (offset, dt)

return HttpResponse(html)

• request is an HttpRequest object, just as in hello and current_datetime.

each view always takes an HttpRequest object as its first parameter

• offset is the string captured by the parentheses in the URLpattern.
• For example, if the requested URL were /time/plus/3/, then offset would be the string ’3’.
• If the requested URL were /time/plus/21/, then offset would be the string ’21’. Note that captured values will always be strings, not integers, even if the string is composed of only digits, such as ’21’.

• we do within the function is call int() on offset. This converts the string value to an integer

• def hours_ahead(request, offset): try: offset = int(offset) except ValueError: raise Http404() dt = datetime.datetime.now() + datetime.timedelta(hours=offset) html = "<html><body>In %s hour(s), it will be %s.</body></html>" % (offset, dt) return HttpResponse(html)

• from django.conf.urls import url, include
• url(r'^time/plus/(\d+)/$', views.hours_ahead, name='hours_ahead')