Django community: Community blog posts RSS
This page, updated regularly, aggregates Community blog posts from the Django community.
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Deploying Django with Fabric
This is a followup to my previous posting Deploying Django with Gunicorn and Supervisor. I have been using Fabric for five or even more years. Fabric is a very flexible and powerful tool for automating deployment routines. My fabfile.py is composed for Git, but you can easily change it to Mercurial or even Subversion. It's much easier to deploy when you use deploy keys, but it is still possible to use HTTP. I personally hate entering passwords, so I would recommend using deploy keys and SSH. I'm assuming that you already have installed nginx and configured your database instance. You will only need two commands to bootstrap and deploy: $ fab staging bootstrap # Clones your project from the repository and perform the initial setup $ fab staging deploy # Pushes your latest changes Obviously, replacing staging with production will change your environment. Here's my typical fabfile.py: import os from contextlib import contextmanager from fabric.api import cd, env, prefix, run, sudo, task PROJECT_NAME = 'YOUR PROJECT NAME' PROJECT_ROOT = '/var/www/%s' % PROJECT_NAME VENV_DIR = os.path.join(PROJECT_ROOT, '.venv') REPO = 'git@bitbucket.org:monmar/%s.git' % PROJECT_NAME env.hosts = [] @task def staging(): env.hosts = ['user@staging-server'] env.environment = 'staging' @task def production(): env.hosts = ['user@production-server'] env.environment ... -
Django Tips #15 Using Mixins With Class-Based Views
I was reading today the book Two Scoops of Django by Audrey and Daniel Roy Greenfeld and found some interesting tips about using class-based views with mixins. Some general rules to use mixins to compose your own view classes, as suggested by Kenneth Love, which I grabbed from the above mentioned book: The base view classes provided by Django always go to the right; Mixins go to the left of the base view; Mixins should inherit from Python’s built-in object type Following an example to illustrate the rules: class FormMessageMixin(object): @property def form_valid_message(self): return NotImplemented form_invalid_message = 'Please correct the errors below.' def form_valid(self, form): messages.success(self.request, self.form_valid_message) return super(FormMessageMixin, self).form_valid(form) def form_invalid(self, form): messages.error(self.request, self.form_invalid_message) return super(FormMessageMixin, self).form_invalid(form) class DocumentCreateView(FormMessageMixin, CreateView): model = Document fields = ('name', 'file') success_url = reverse_lazy('documents') form_valid_message = 'The document was successfully created!' In a similar way you could reuse the same FormMessageMixin in a UpdateView for example, and also override the default form_invalid_message: class DocumentUpdateView(FormMessageMixin, UpdateView): model = Document fields = ('name', ) success_url = reverse_lazy('documents') form_valid_message = 'The document was successfully updated!' form_invalid_message = 'There are some errors in the form below.' Since Django 1.9 we have the built-in mixins LoginRequiredMixin and UserPassesTestMixin. ... -
Acing Your Architecture Interview
My most memorable interview started with an entirely unexpected question: “How well do you remember calculus?” I smiled and said that it had been some years, and that I was rather out of practice. Nonetheless we spent the next hour trying to do calculus, which I bombed spectacularly. Many people have similar misgivings about “architecture interviews”, which are one of my favorite interviews for experienced candidates from within the internet industry, and I decided to write up my algorithm for approaching these questions. Before jumping in, a few examples of typical architecture interview questions: Design the architecture for Facebook, Twitter, Uber, Foursquare or a similarly well known product. Diagram a basic web application of your choice. Design a reliable website similar to a newspaper’s website. Design a scalable API to power a mobile game. From that starting point, the interviewer will either give you more constraints to solve for (“your database starts to get overloaded”), or ask you to think of ways that your system will run into scaling problems and how to address them (“well, first off, I think we’d run out of workers to process incoming requests”). The basic algorithm to this class of interviews is: Diagram your ... -
uWSGI File Wrapper and Python 3.5
A couple of weeks ago we hit a small but hard to track issue in one of our clients. They opened an issue telling us that the downloaded files appeared as corrupt. After closer examination, the downloaded files had 0 bytes. The HTTP response was a solid 200 OK with a 0 bytes file attachment. This was very strange, given that no automatic error reports had been triggered and there was clearly an error. Morover we noticed that this issue in particular happened whenever the backend Django app returned a file in the response. This is quite rare in a production environment, given that you most certainly don’t want the Django app handling files, but rather links to the files. However, one usual exception for this rule are small dynamic reports (for bigger ones you’ll want to send an email link when its ready). On the Django logs we could clearly see that the reports were properly created and no errors were present neither there nor in the nginx logs. That left us to take a peek at the application server logs, in this case, uWSGI. It was there that we got to see the following:io.UnsupportedOperation: fileno During handling of ... -
Fail Open and Layer Policy
Around 2009, the Dynamo paper materialized into Cassandra. Cassandra escaped Facebook in the fashion of the time: an abrupt code bomb errupting into existence with little ongoing maintenance. Maintaining early versions of Cassandra was itself an explosive experience, and those who ran early versions developed a shared joke that Cassandra was a trojan horse released to blot out progress by an entire generation of Silicon Valley startups. Working at Digg and running Cassandra 0.6, we didn’t laugh much. While operationally it was a bit of a challenge, it introduced me to what felt like a very novel idea at the time: Cassandra and similarly designed NoSQL databases were bringing scalability to the masses by only providing operations that worked well at scale. Sure, later they released CQL and that rigid enforcement faded, but the idea that you can drive correct user behavior by radically restricting choice was a very powerful one. A couple jobs later, I joined a team which was exploring the logical extremes of this concept; we had extremely rigid service provisioning and configuration tools, which only allowed a very specific shape of service run in a very specific way (colloquially, The Right Way). Our customers loved that ... -
How to Create a Password Reset View
For this short tutorial we will be using the django.contrib.auth views to add a password reset functionality to your Django application. The process of reseting passwords involves sending emails. For that matter we will be using console email backend to debug and check if everything is working. In the end of this tutorial I will also provide resources to properly configure a prodution-quality email server. Dependencies Basically all you need is to have django.contrib.auth in your INSTALLED_APPS and a email service properly configurated (for production). During the development we can use file/console email backend. settings.py INSTALLED_APPS = [ ... 'django.contrib.auth', ] EMAIL_BACKEND = 'django.core.mail.backends.console.EmailBackend' # During development only Implementing We need 4 different views: password_reset: Form where the user submit the email address password_reset_done: Page displayed to the user after submitting the email form. Usually with instructions to open the email account, look in the spam folder etc. And asking for the user to click on the link he will receive. password_reset_confirm: The link that was emailed to the user. This view will validate the token and display a password form if the token is valid or an error message if the token is invalid (e.g. was already used or ... -
Thoughts on Envoy's Design
A couple days ago Lyft released Envoy, which is a pretty exciting take on a layer 7 proxy. This is an area that I’ve been thinking about a fair amount, both in terms of rolling out widespread quality of service, as well as request routing in heavily polygot environments. Before getting into my thoughts, let’s take a quick recap of common load balancing strategies. Historically, the most common approach to load balancing was to use a centralized load balancer of some kind and to route all traffic to it. These LBs can be done at a per-service level like ELBs, or can be very sophisticated hardware like F5s. Increasingly these seem to be going out of style. In part due to their cost and complexity, but my take is that their lack of popularity is more driven by a lack of flexiblity and control. As a programmer, it’s relatively intuitive to programmatically manage HAProxy, in a way that most centralized load balancers don’t offer. (And it’s not even that easy to manage HAProxy programmatically, although it’s making steady progress.) On the other end of the continuum, there is per-process load balancing like Finagle, where each one of your processes maintains ... -
Caktus Group @ PyData Carolinas 2016
Tomorrow marks the official beginning of PyData Carolinas 2016 (though technically, the tutorials started today). This is the first time PyData has hosted a conference in our area. We’re especially proud of the way local leaders and members of meetups like TriPython, TechGirlz, Girl Develop It RDU, and PyLadies have worked in tandem to put this event together for the Python community. Caktus will be at PyData tomorrow and Friday as a Silver sponsor. We’re glad to be in the company of esteemed sponsoring organizations like IBM, RENCI, Continuum Analytics, and the Python Software Foundation. Come see us at the following PyData events and talks! Wednesday, September 14th 7:00PM - 8:00PM Evening Social at the 21c Museum Hotel Join us after the tutorials with a social hosted by the Durham Convention Center. More details here. Thursday, September 15th 8:30AM - 5:30PM Caktus Booth We’ll have a booth with giveaways for everyone plus a raffle. We’ll also have a display of OpenDataPolicingNC, a project Caktus CTO Colin Copeland helped lead; it received a White House nod for Code for Durham. 11:30AM - 12:10PM Reach More People: SMS Data Collection with RapidPro (Room 1) Erin Mullaney (Caktus) and Rebecca Muraya (TransLoc) will ... -
Django Shortcuts
This module is a collection of helper classes generally used in view functions/classes. All the shortcuts are available in the module django.shortcuts. render Params: def render(request, template_name, context=None, content_type=None, status=None, using=None) Shortcut for: content = loader.render_to_string(template_name, context, request, using=using) return HttpResponse(content, content_type, status) There is also render_to_response, the only difference is that it does not pass the request to the context. redirect Params: def redirect(to, *args, **kwargs): Returns an HttpResponseRedirect (or HttpResponsePermanentRedirect) to the appropriate URL for the arguments passed. The arguments could be: A model: the model’s get_absolute_url() function will be called. A view name, possibly with arguments: urls.reverse() will be used to reverse-resolve the name. A URL, which will be used as-is for the redirect location. Shortcut for: def post_view(request, post_id): post = Post.objects.get(pk=post_id) return redirect(post) # equivalent to: return HttpResponseRedirect(post.get_absolute_url()) def post_view(request, post_id): return redirect('post_details', id=post_id) # equivalent to: return HttpResponseRedirect(reverse('post_details', args=(post_id, ))) def relative_url_view(request): return redirect('/posts/archive/') # equivalent to: return HttpResponseRedirect('/posts/archive/') def absolute_url_view(request): return redirect('https://simpleblog.com/posts/archive/') # equivalent to: return HttpResponseRedirect('https://simpleblog.com/posts/archive/') See more in this post about the redirect function. get_object_or_404 Params: def get_object_or_404(klass, *args, **kwargs): Shortcut for: try: return Model.objects.get(pk=1) except Model.DoesNotExist: raise Http404() get_list_or_404 Params: def get_list_or_404(klass, *args, **kwargs): Shortcut for: obj_list = list(Model.objects.filter(title='test')) if ... -
QoS, Cost & Quotas
One of the most exciting inversions thats comes with scaling a company is the day when someone repeats the beloved refrain that engineers are more expensive than servers, followed by a pregnant pause where you collectively realize that the lines have finally crossed: servers have become more expensive than engineers. But what do you do with this newfound knowledge? Why, you kick off a Cost Accounting or Efficiency project to start optimzing your spend! These projects tend to take on a two pronged approach of: identify some low-hanging fruit for show immediate wins, and begin to instrument and tag your costs to create transparency into how your spends actually work. The later gets interesting quickly. First, let’s start with the fundamental unit of infrastructure cost: a server. For each server you probably have a role (your mysql01-west is probably in a mysql role), and for each role you can probably assign an owner to it (perhaps your database team in this case). Now you write a quick script which queries your server metadata store every hour and emits the current servers and owners into Graphite or some such. A job well done! Your work here is over… until later that ... -
A Brief Introduction to Django Channels
Django has long been an excellent web framework. It has helped many developers and numerous businesses succeed over the years. But before the introduction of Channels, Django only supported the http protocol well. With the gradual evolution of the web technologies, standing here in 2016, supporting http only is simply not enough. Today, we are using websockets for real time communications, WebRTC is getting popular for real time collaboration or video calling, HTTP/2 is also being adapted by many. In the current state of the web, any modern web framework needs to be able to support more and more protocols. This is where Django Channels come into play. Channels aim at adding new capabilities to Django, including the support for modern web technologies like websockets or http2. How does “Channels” work? The idea behind Channels is quite simple. To understand the concept, let’s first walk through an example scenario, let’s see how Channels would process a request. A http/websocket request hits the reverse proxy (ie, nginx). This step is not compulsory but we’re conscious developers and always make sure our requests first go through a hardened, battle proven reverse proxy before it hits our application server Nginx passes the request ... -
Testing dates in Django
Django makes unit & functional testing easy (especially with WebTest). Tests on routing, permissions, database updates and emails are all straightforward to implement but how do you test dates & time? You might for example want to test regular email notifications. -
Fixing "Symbol not found: _PyUnicodeUCS2_Compare and _PyUnicodeUCS2_AsASCIIString"
I've got a new client with a legacy Django project running on Python 2.7 with Pandas. When I was configuring my local OS X environment I got a bunch of nasty errors: ImportError: dlopen(/Users/mike/.pyenv/versions/project/lib/python2.7/site-packages/pandas/hashtable.so, 2): Symbol not found: _PyUnicodeUCS2_Compare Referenced from: /Users/mike/.pyenv/versions/project/lib/python2.7/site-packages/pandas/hashtable.so Expected in: flat namespace in /Users/mike/.pyenv/versions/project/lib/python2.7/site-packages/pandas/hashtable.so My first assumption was to upgrade Pandas from 0.15.1 to the most recent 0.18.1, but that didn't help. I rolled back to Pandas 0.15.1 to avoid any possible regressions. After tens minutes of reading traceback messages and googling, I managed to fix that error with running $ pip install -U cython. After that I've got: ImportError: dlopen(/Users/mike/.pyenv/versions/2.7.12/envs/project/lib/python2.7/site-packages/numpy/core/multiarray.so, 2): Symbol not found: _PyUnicodeUCS2_AsASCIIString Referenced from: /Users/mike/.pyenv/versions/2.7.12/envs/project/lib/python2.7/site-packages/numpy/core/multiarray.so Expected in: flat namespace in /Users/mike/.pyenv/versions/2.7.12/envs/project/lib/python2.7/site-packages/numpy/core/multiarray.so It seemed to be fixed in the most recent Numpy version, so I ran $ pip install -U numpy pandas, and the error disappeared. I hope this short blog post will save your time. You're welcome to share your experience with fixing similar not obvious issues. -
Django Tips #14 Using the Messages Framework
Keeping the users of your application aware of what is going on makes a huge difference in the user experience. If there is something users hate more than slow applications, it is applications that does not communicate with them. – The user clicks in a save button. – Nothing happens. – So, did it save the data or not? – User reaction after a couple of (mili)seconds: *Click!* *Click!* *Click!* *Click!* Let’s make our users more confident and comfortable, shall we? Configuration By default, a brand new Django project already comes with the messages framework installed. If you did not change anything in relation to the messages framework, just skip to the next section. Otherwise, set it up: INSTALLED_APPS django.contrib.messages MIDDLEWARE or MIDDLEWARE_CLASSES in older versions: django.contrib.sessions.middleware.SessionMiddleware django.contrib.messages.middleware.MessageMiddleware TEMPLATES context_processors django.contrib.messages.context_processors.messages Message Levels and Tags Constant Level Tag (for CSS) Purpose DEBUG 10 debug Development-related messages that will be ignored (or removed) in a production deployment INFO 20 info Informational messages for the user SUCCESS 25 success An action was successful WARNING 30 warning A failure did not occur but may be imminent ERROR 40 error An action was not successful or some other failure occurred By default, Django will ... -
Deploying Django with Gunicorn and Supervisor
Here in Monmar we deploy all Django applications with Gunicorn and Supervisor. I personally prefer Gunicorn to uWSGI because it has better configuration options and more predictable performance. In this article we will be deploying a typical Django application. We won't be using async workers because we're just serving HTML and there are no heavy-lifting task in background. I'm assuming that our Django project was created with Cookiecutter Django, an awesome boilerplate developer by Daniel Roy Greenfeld. I strongly recommend using it for every new Django project. Our requirements/production.txt file should already contain these two packages: # WSGI Handler # ------------------------------------------------ gevent==1.1.1 gunicorn==19.6.0 So, we only need to SSH to the server, create a virtualenv and populate it with packages: $ virtualenv --python=python3.5 .venv $ source .venv/bin/activate $ pip3 install -r requirements.txt Next, we're going to add missing configs to our working copy: $ mkdir -p deploy/production && cd deploy/production $ touch gunicorn.conf.py nginx.conf run.sh supervisor.conf I'm providing real configuration files we're using for our company website. So, please update it for your project needs. gunicorn.conf.py bind = 'unix:/tmp/gunicorn-monmar.sock' workers = 2 timeout = 30 nginx.conf upstream monmar { server unix:/tmp/gunicorn-monmar.sock fail_timeout=0; keepalive 60; } server { listen 80; listen ... -
How to Work With AJAX Request With Django
There are many scenarios where you may want to use AJAX requests in your web application. It is a great resource that enables web applications to be faster and more dynamic. For this short tutorial I will be using jQuery to ease the implementation. You can choose a different framework, or even implement it using JavaScript only. But the concept will remain the same. Initial Setup Here is how my base.html template looks like: {% load static %}<!doctype html> <html> <head> <meta charset="utf-8"> <title>{% block title %}Default Title{% endblock %}</title> <link rel="stylesheet" type="text/css" href="{% static 'css/app.css' %}"> {% block stylesheet %}{% endblock %} </head> <body> <header> ... </header> <main> {% block content %} {% endblock %} </main> <footer> ... </footer> <script src="https://code.jquery.com/jquery-3.1.0.min.js"></script> <script src="{% static 'js/app.js' %}"></script> {% block javascript %}{% endblock %} </body> </html> The jQuery library and all the JavaScript resources stays in the end of the HTML page for two reasons: to guarantee the DOM will be loaded whe the script is executed and to avoid inline scripts (at least scripts that uses jQuery). All the extra or page specific JavaScript goes inside the {% block javascript %}{% endblock %} block. Sample Scenario Let’s say you want ... -
Django to Ember #1
If you know Django and want to learn Ember (or vice-versa), this guide is for you. To get started, let's see what happens when a user opens the `/contact` page in both frameworks. -
Simple qgis plugin repo
At my company, we sometimes build QGIS plugins. You can install those by hand by unzipping a zipfile in the correct directory, but there's a nicer way. You can add custom plugin "registries" to QGIS and QGIS will then treat your plugins just like regular ones. Here's an example registry: https://plugins.lizard.net/ . Simple, right? Just a directory on our webserver. The URL you have to configure inside QGIS as registry is that of the plugins.xml file: https://plugins.lizard.net/plugins.xml . The plugins.xml has a specific format: <?xml version="1.0"?> <plugins> <pyqgis_plugin name="GGMN lizard integration" version="1.6"> <description>Download GGMN data from lizard, interpolate and add new points</description> <homepage>https://github.com/nens/ggmn-qgis</homepage> <qgis_minimum_version>2.8</qgis_minimum_version> <file_name>LizardDownloader.1.6.zip</file_name> <author_name>Reinout van Rees, Nelen &amp; Schuurmans</author_name> <download_url>https://plugins.lizard.net/LizardDownloader.1.6.zip</download_url> </pyqgis_plugin> .... more plugins ... </plugins> As you see, the format is reasonably simple. There's one directory on the webserver that I "scp" the zipfiles with the plugins to. I then run this script on the directory. That script extracts the (mandatory) metadata.txt from all zipfiles and creates a plugins.xml file out of it. A gotcha regarding the zipfiles: they should contain the version number, but, in contrast to python packages, the version should be prefixed by a dot instead of a dash. So no myplugin-1.0.zip but myplugin.1.0.zip. ... -
How to Create a One Time Link
Django uses a very interesting approach to generate the Password reset tokens. I’m not really a security expert, neither I’m very familiar with cryptography algorithms, but it is very safe and reliable. Before I elaborate a little be more on the one-time-link generation, I wanted to discuss about the Django’s PasswordResetTokenGenerator implementation. Because what we will be doing is actually extending this particular class to fit our needs. Generally speaking, Django generate a token without persisting it in the database. Yet, it still have the capabilities of determining whether a given token is valid or not. Also the token is only valid for a defined number of days. The default value for the Password Reset Token is 7 days, and it can be changed in the settings.py by changing the value of PASSWORD_RESET_TIMEOUT_DAYS. The class have two public methods: make_token(user) check_token(user, token) The make_token method will generate a hash value with user related data that will change after the password reset. Meaning, after the user clicks on the link with the hash and proceed to the password reset, the link (or the hash) will no longer be valid: def _make_hash_value(self, user, timestamp): # Ensure results are consistent across DB backends ... -
Django Tips #13 Using F() Expressions
In the Django QuerySet API, F() expressions are used to refer to model field values directly in the database. Let’s say you have a Product class with a price field, and you want to increase the price of all products in 20%. A possible solution would be: products = Product.objects.all() for product in products: product.price *= 1.2 product.save() Instead you could use an F() expression to update it in a single query: from django.db.models import F Product.objects.update(price=F('price') * 1.2) You can also do it for a single object: product = Product.objects.get(pk=5009) product.price = F('price') * 1.2 product.save() But take care with this kind of assignment. The F() object persist after saving the model. product.price # price = Decimal('10.00') product.price = F('price') + 1 product.save() # price = Decimal('11.00') product.name = 'What the F()' product.save() # price = Decimal('12.00') So, basically after updating a field like that, product.price will hold an instance of django.db.models.expressions.CombinedExpression, instead of the actual result. If you want to access the result immediately: product.price = F('price') + 1 product.save() print(product.price) # <CombinedExpression: F(price) + Value(1)> product.refresh_from_db() print(product.price) # Decimal('13.00') You can also use it to annotate data: from django.db.models import ExpressionWrapper, DecimalField Product.objects.all().annotate( value_in_stock=ExpressionWrapper( F('price') * F('stock'), ... -
Dealing With QueryString Parameters
It is kinda tough to describe what the problem really is. But, do you know when you are creating an interface where you provide pagination, filters and ordering, and you are making it controlling it via URL Get parameters? For instance if you have different options for ordering, you might think of something like that: <div class="dropdown"> <button class="btn btn-default dropdown-toggle" type="button" data-toggle="dropdown"> Order by </button> <ul class="dropdown-menu"> <li><a href="?order=name">Name (a-z)</a></li> <li><a href="?order=-name">Name (z-a)</a></li> <li><a href="?order=price">Price</a></li> <li><a href="?order=date">Date</a></li> </ul> </div> Basically you would be sending the user to the very same page, but passing a GET parameter named order, where you could do something like that: def products_list(request): products = Product.objects.all() order = request.GET.get('order', 'name') # Set 'name' as a default value products = products.order_by(order) return render(request, 'products_list.html', { 'products': products }) PS: This is a minimalist example, if you pass an invalid parameter directly in the querystring you will make queryset break. I will avoid adding extra validations so we can focus on the objective of this article. So far so good. But the problem starts to appear when you add new control, also via GET parameter. Lets say a pagination: <ul class="pagination"> {% for i in page_obj.paginator.page_range %} ... -
Better Python Object Serialization
Serialization is everywhere. Notably for me: JSON web APIs and structured logs. And yet, general approaches to serialize arbitrary objects to JSON are rather clunky. Fortunately there’s a gem in the Python standard library that makes it easy and elegant. -
Django Tips #12 Disabling Migrations to Speed Up Unit Tests
The model migrations are certainly a great feature of the Django framework. But, when it comes down to running tests, it really slows down the process. Especially if your migration history is big. This is a simple tip to speed up your tests. I like to create a separate settings file for this tweaks. tests_settings.py from settings import * # Custom settings goes here And then to run the tests: python manage.py test --settings=myproject.tests_settings --verbosity=1 Django >= 1.9 One option is using the MIGRATION_MODULES setting, which is intended to define a custom name for an app’s migration module. If you set None instead, Django will ignore the migration module. from settings import * MIGRATION_MODULES = { 'auth': None, 'contenttypes': None, 'default': None, 'sessions': None, 'core': None, 'profiles': None, 'snippets': None, 'scaffold_templates': None, } Django < 1.9 This is a possible solution if you are using a version prior to 1.9. Actually, I still prefer to use it nowadays. Because I don’t need to set each app. from settings import * class DisableMigrations(object): def __contains__(self, item): return True def __getitem__(self, item): return 'notmigrations' MIGRATION_MODULES = DisableMigrations() Older Django Versions (using South) Hold tight: SOUTH_TESTS_MIGRATE = False Damn! It could even live ... -
Package of the Week: Pendulum
Pendulum is a Python library to make your life easier when it comes down to work with date/time. Installation pip install pendulum A few dependencies will be installed: pytz, tzlocal and python-dateutil. Just the python-dateutil itself is already great – but pendulum offers a few more tweaks. Usage import pendulum now = pendulum.now() # '2016-08-18 20:24:52' Let’s keep the now variable for the next examples. add now.add(days=1) # '2016-08-19 20:24:52' Accepts days, months, years, hours, minutes, seconds, microseconds, weeks. now.add(weeks=1, hours=2) # '2016-08-25 22:24:52' subtract now.subtract(weeks=1) # '2016-08-11 20:24:52' age birthday = pendulum.create(1988, 10, 22) birthday.age # 27 diff now = pendulum.now('Europe/Helsinki') future = now.add(hours=12) past = now.subtract(years=50, days=12) future.diff() # '<Period [11 hours 59 minutes 41 seconds]>' future.diff_for_humans() # '11 hours from now' past.diff_for_humans() # '50 years ago' delta delta = now - last_week delta.start # <Pendulum [2016-08-05T00:28:26.207225+03:00]> delta.end # <Pendulum [2016-08-12T00:28:26.207225+03:00]> delta.in_days() # 7 delta.in_hours() # 168 delta.in_weekdays() # 6 delta.in_words() # '1 week' interval it = pendulum.interval(days=15) it.weeks # 2 it.days # 15 it.in_hours() # 360 it.in_words() # '2 weeks 1 day' is_ now.is_birthday() now.is_future() now.is_past() now.is_monday() now.is_tuesday() now.is_wednesday() now.is_thursday() now.is_friday() now.is_saturday() now.is_sunday() now.is_today() now.is_yesterday() now.is_tomorrow() now.is_leap_year() now.is_long_year() now.is_same_day() now.is_weekday() now.is_weekend() now = pendulum.now() # 2016-08-18 20:24:52 ... -
Exploring Django Utils #2
Last week I started a post series exploring the django.utils module. In this second part I will be focusing more on the html module. HTML Module: django.utils.html escape Returns the given text with ampersands, quotes and angle brackets encoded for use in HTML. from django.utils.html import escape escape("<strong style='font-size: 12px'>escaped html</strong>") '&lt;strong style=&#39;font-size: 12px&#39;&gt;escaped html&lt;/strong&gt;' It will cause already escaped strings to be escaped again: escaped_html = escape("<strong>escaped html</strong>") # '&lt;strong&gt;escaped html&lt;/strong&gt;' escape(escaped_html) # '&amp;lt;strong&amp;gt;escaped html&amp;lt;/strong&amp;gt;' If this is a concern, use conditional_escape() instead. conditional_escape escaped_html = conditional_escape("<strong>escaped html</strong>") # '&lt;strong&gt;escaped html&lt;/strong&gt;' conditional_escape(escaped_html) # '&lt;strong&gt;escaped html&lt;/strong&gt;' format_html This function is similar to str.format, but it will conditional escape all the arguments. Prefer to use it to build small HTML fragments instead of str.format or string interpolation, as it is safer. from django.utils.html import format_html format_html('<div class="alert {}">{}</>', 'warning', 'Watch out!') '<div class="alert warning">Watch out!</>' Safely format HTML fragments: format_html('<div class="alert {}">{}</>', '<script>alert(1);</script>', 'Watch out!') '<div class="alert &lt;script&gt;alert(1);&lt;/script&gt;">Watch out!</>' format_html_join A wrapper of format_html, for the common case of a group of arguments that need to be formatted using the same format string. format_html_join('\n', '<p>{}</p>', ['a', 'b', 'c']) <p>a</p>\n<p>b</p>\n<p>c</p> Another example: data = [ ['success', 'Success message'], ['warning', 'Watch out!'], ['danger', ...
