Matching DateTime objects in test cases with Django Rest Framework

If your model has a date_created or modified etc. kind of object(s) probably you will face a datetime object mismatch issue while asserting equality of your dictionary object with the rendered response dictionary. So, I have created a small function which will help you resolve it.

 

DATETIMEHELPER = lambda x : str(x.isoformat().split('.')[0])+'Z'

 

Now, you can call your data object as :

data = {...,"date_created":DATETIMEHELPER(self.model_name.date_created),...}
response.render()
self.AssertEqual(json.dumps(response.content), data)

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Implementation of Graph DS using Python and BFS,DFS covered with iteration

This post will be mostly code. Please use proper indenting cuz Python otherwise will make your life hell. If you’re using Sublime go to, set Convert Indentation to tabs.

Gist : I have used the collections.defaultdict dict DT for implementing a dict of sets.
Vertices have been stored as adjacency list kind of elements as a dictionary. The code is raw and may have errors ( though no compilation error as of the post’s writing). Please comment for additional details. This is purely for testing purposes.


 

graph            A Graph.

 



from collections import defaultdict

#The Graph will be a dictionary of sets
class Graph():

def __init__(self, connections, directed = False):
self.graph = defaultdict(set)
self.directed = directed
self.add_connections (connections)

def add_connections(self, connections):
for node1,node2 in connections:
self.add_connection(node1,node2)

def add_connection(self, node1, node2):
self.graph[node1].add(node2)
if not self.directed:
self.graph[node2].add(node1)

def remove(self, node):
#removes all references to the node
#Use iteritems for dict items like k,v in dictname.iteritems():
for n,cons in self.graph.iteritems():
try:
#Removing from a set involves setname.remove(element)
cons.remove(node)
except KeyError:
pass
try:
#Removing from a dictionary involves rem dict_element_name
del self.graph[node]
except KeyError:
pass

def isconnected(self, node1, node2):
if node1 in self.graph[node2] or node2 in self.graph[node1]:
return True
return False

def dfs(self,start):
#If start node does not exist, return None (search is futile)
if start not in self.graph:
return None
#Start with an empty set
visited = set()

#To return unse ( which is not a set
unset = []
#Initially fill stack with start vertex
stack = [start]

#While stack is not empty keep repeating this algorithms
while stack:
#Take the first element of stack (pop means last inserted , aggressive)
vertex = stack.pop()
#If vertex has not been visited yet, add it to visited and look for all the element in graph[vertex]
if vertex not in visited:
visited.update(vertex)
unset.append(vertex)
stack.extend(self.graph[vertex] - visited)
return unset

def bfs(self, start):
if start not in self.graph:
return None
visited = set()
queue = [start]
unset = []
while queue:
vertex = queue.pop(0)
if vertex not in visited:
visited.update(vertex)
unset.append(vertex)
queue.extend(self.graph[vertex] - visited)
return unset

#Should work but not tested
def findpath(self,v1, v2):
m = bfs(v1)
if v2 in m:
return m[:m.index(v2)+1]
return None

 

An open source ‘Good’ Web Application stack

Web Framework – Django : Python or Flask : Python

Server – Apache HTTP Server

Database – MySQL

Virtual Environment – Vagrant (You want Docker ?)

Task Watcher – Grunt

Database Agent – Sequel Pro (Macbook <3)

Server – AWS EC2

Media Server (if any) – AWS S3

Add some cute JS, CSS3, HTML5 etc. to the front end.

I guarantee some considerable amount of your savings in your next web app budget!

Django Basics : Part – 3

 

 

So, I hope you managed to setup the django project and could visit the welcome page after running the server. Now, this tutorial contains the interesting part. Creating an app that works !!!! Interesting ? Yes, certainly, for I will guide you in this tutorials as how to create models, url configurations, map a basic relationship between models, migrate the models to create suitable relations in the DB (SQLLite in your case), write code to query the database and also, run the django shell ( a ridiculously important part of learning django), apart from the primary task of getting the application run on the default django server.

In some future tutorial I will guide you how to setup django with Apache server and MySQL.

django-python

Let’s now create an app within the musicStore project.


 

Create the app

$python manage.py startapp musicApp

This creates all the necessary files inside the musicStore/musicApp/ directory.


 

Confirm if the following files were created after this command. 

musicStore/musicApp/__init__.py
musicStore/musicApp/apps.py – Configurations for the app for django settings. We won’t usei t in this tutorial, new addition in 1.9
musicStore/musicApp/models.py – Modles are created here
musicStore/musicApp/views.py  – Views are created here (Kind of Controller logic analogous to MVC)
musicStore/musicApp/urls.py – URL routing information, maps URLS to Views
musicStore/musicApp/admin.py – Admin settings for the app useful for the admin console
musicStore/musicApp/migrations/ – Contains all the migrations file so that any database change is recorded and could be used, reverted to etc.
musicStore/musicApp/tests.py  – File to contains unit tests. Mock-Brraintree would be a good start which I will cover in some future tutorial


 

“Projects vs. apps

What’s the difference between a project and an app? An app is a Web application that does something – e.g., a Weblog system, a database of public records or a simple poll app. A project is a collection of configuration and apps for a particular website. A project can contain multiple apps. An app can be in multiple projects.”

-From the django website


Model

Screen Shot 2016-03-01 at 3.52.47 PM

We can see that there are two models, Album and Artist. One Album can have only 1 Artist but 1 Artist can publish multiple Albums. This relationship is defined by the Foreign Key field in Album, album_artist and hence, every Artist object will have an album_set object containing the list of Albums that it may have, and this is a django property.

You will also observe a Meta inner class in the model. this is used to define important metadata pertaining to the model, like ordering of model objects if displayed in a list somewhere, name it will be known as in the DB, name it will be known as in the admin console etc and many more. Full documentation is available in : https://docs.djangoproject.com/en/1.9/intro/tutorial02/

 


Migrations 

Screen Shot 2016-03-01 at 2.02.28 PM
makemigrations command

 

Screen Shot 2016-03-01 at 2.02.44 PM
sqlmigrate <migration_id> command

 

Screen Shot 2016-03-01 at 2.02.56 PM
migrate command

$python manage.py makemigrations
It tells Django that some changes to our models have been made, and are to be stored as a migration in the musicapp/migrations/ directory.

At this point, we can either directly migrate to apply those changes from the migration file or we can check the actual set of SQL commands that are going to be executed by django. The former is done by the migrate command while the latter can be performed by the sqlmigrate <migration_id> command.

In short, makemigrations forms a migration file but doesn’t apply any changes yet. migrate actually applies the changes recorded in the migration file.


 

__str__ method of models

Screen Shot 2016-03-01 at 2.16.35 PM

Now, we add the __str__ method in the models because it provides us the string representation of an object whenever queried. You’ll understand the importance once you start using the shell or the admin console, apart from others which utilise it.


 

Using the django shell

$cd ~/Desktop/musicStore/
$python manage.py shell
>>>from musicApp.models import Artist
>>>Artist.objects.all()
[]
>>>from musicApp.models import Album
>>>Album.objects.all()
[]

First of all, congrats on getting access to the django shell. Here you can do a lot of things, including querying the django database and everything python. it is useful for small fixtures like checking if some value is being returned the way it is supposed to be, before applying changes in the UI etc. You will learn a lot more about it in the tutorial and coming posts.


 

Adding models objects – Continue the terminal from the previous section

>>> artist1 = Artist(artist_name = “The Chainsmokers”, artist_twitter_id = “TheChainsmokers”, slug = “thechainsmokers”)

>>> artist2 = Artist(artist_name = “Imagine Dragons”, artist_twitter_id = “ImagineDragons”, slug = “imgd”)

Add Artists

Screen Shot 2016-03-01 at 3.51.43 PM.png
Add Albums

 

Note : As you can see, we are adding stuff via the django shell but evenetually, there will be forms in the web page in the form of django forms or HTML forms which will help you add objects. this addition via shell is for illustrative purposes. 

artist1.album_set gives you the albums related to the artist1 and so on. This means, if A has a Foreign Key B, any instance of B, say b, can query all the related instances of A as b.a_set.all() and so on.



To be continued….

Next tutorial will be on using URLS and Views to query these model objects. 

 

Django Basics : Part-2

magic-pony-django-wallpaper

‘M happy to be back to  you all.

So, this post will help you setup your first django web app and will also fill in details and notes on how many of its small components work and interact. I have just explained the basic components in my previous post which is the first part without any hint of python-django code. Let me do that this time and get you acclimatized to the things that may go wrong often as well, apart from the things that will go right! This part 2 tutorial will comprise a few defined set of steps.
Before we begin I want you to refer this tutorial if you want to know anything about writing your first django app beyond this tutorial please visit : https://docs.djangoproject.com/en/1.9/intro/tutorial01/
Also, I assume that you have python 2.7 installed in your machine as this tutorial will be on django 1.9x and python 2.7. this tutorial should work on both Windows and Unix based systems, including Mac, though the directory structure is assumed to be of Mac. One can use it in Windows by making slight changes to the tutorial’s instructions.

So, let’s begin…

To know how to install pip please refer my tutorial on installing pip. All the commands below are to be executed in the terminal.

Install django

$pip install django

 

Check if Installation is successful

$python
>>>import django
>>>print django.get_version()

This will tell you the version of django that you just installed. If you did not install it properly you will see error messages in executing the first or the second function.
When done, type :

>>exit()
or
>>>ctrl + D

to exit from the python prompt

 

Create your project directory and ‘cd’ to it

$cd ~/Desktop/
$mkdir djangoTutorialStuff
$cd djangoTutorialStuff

 

Make a django project

$django-admin startproject musicStore 

Check if it worked and you may want to check the directory structure too.
$cd musicStore

You’re gonna see two things inside the project. A manage.py file and a musicStore directory. The manage.py is the principle python file governing the whole project. Anything you want to do with the project goes like python manage.py <your_command>.

Confirm if the musicStore directory has the following files : 

__init__.py  – Tells that this directory is a django directory
settings.py  – Contains the overall settings of the whole django project (musicStore)
urls.py  – Contains the root url configurations for the musicStore project
wsgi.py  – contains the application callable which the application server uses to communicate with your code

As of now, only the project has been setup without any setting changes.
Next you have to create app(s) of your choices to actually do something of its own. These apps are pluggable django entities that can also be used by other projects like musicStore does.  Apps will be created in the next tutorial – Part 3 !

Confirm if project setup works 

$cd ~/Desktop/musicStore
$python manage.py runserver

Verify if the following output shows up :

Performing system checks…
System check identified no issues (0 silenced).
You have unapplied migrations; your app may not work properly until they are applied.
Run ‘python manage.py migrate’ to apply them.
February 29, 2016 – 15:48:41
Django version 1.9.1, using settings ‘musicStore.settings’
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

Now visit : http://127.0.0.1:8000/

If django welcome page shows up you’re good to go. If not, please leave a comment.

Install pip – D awesome Python Package Manager

python-pip-and-the-staff-group-a

Folks, install pip n enjoy your python installations now :

  1. Visit https://bootstrap.pypa.io/get-pip.py
  2. Copy the content and save in a file naming it as get-pip.py
  3. Run the following command from the CLI in the directory where you saved the aforementioned file.
    $python get-pip.py
  4. If you don’t have permissions try :
    $sudo python get-pip.py

Congrats, pip is now installed in your system. Keep updating it regularly!

Now onwards, all you need to do to install a python package is:
$ sudo pip install <package name>