Notes from other talks and various ideas collected

find out how to do the rst-class: build correctly with Hierloglyph

TDD

add distinction between integration and unit tests and when mocking comes into consideration

add a way to set up correctly the whole flow in Emacs with the right setup hook

propose a lighting talk about Emacs showing the whole configuration

• from zero to intellisense with Jedi and other libraries.
• show how to install things on a clean Emacs environment

Interesting links

• taohe-lafs
• python-rex, to use Perl-like regex in Python easily (using a cache)
• iktomi, something used to build web apps
• getsentry, use the hosted version
• mailing list: code-quality@python.org

Sentry

• doing business with a completely open source project
• don’t try to compute with people hosting themselves
• try to minimize companies that are more a pain than anything else
• do the project you love and users will also love it

Disqus

• phabricator to view the diffs
• review that
• CI done by jenkins (before commited)
• push with GIT
• put all the commits in a daily deploy
• 0-8 daily deploys

django + celery + postgres + rabbit

Problems with current stack

• high concurrency
• need to isolate things
• isolate features (to fasten the loop)
• fun and experimentation

(nginx modules for example, or LUA)

Other interesting things

• use mixins (do only one thing)

Some libraries done by Disqus:

• django-mailviews
• nydus (for redis)
• gargoyle (for application switches)

SF jobs, seems interesting.

suggest a possible way to force the hooks

Static analysis

• tokenize module handles all the tokenization of things

Emacs show

Create a minimal working.

• auto completion with Jedi, and code navigation
• handling virtualenv
• git integration with magit
• running tests
• jumping to things easily

ed solution: https://www.getsentry.com/pricing/

Git internals

• git uses SHA1 hashes to keep track of everything, which is like a fingerprint
• use git cat-file -p/-t to show what is going on
• traditional SCM use delta differences, which would sound more efficient, but in git there is a copy of the whole tree, with linked lists used.
• you can use “git checkout attach-head” to attach after you’re actually detached

Next iteration of GUI applications

• generated by generator/iterator ideas, using PEP 342 and PEP 380

Building to scale

SQL

• Disqus runs on Postgres.
• You can use SQL by doing more or less everything.
• scaling is about predictability
• what can we do to improve SQL?
• Redis is the best simple technology that works

Caches

Counters

• Using Redis as a cache for updating things
• Redis nodes are easily horizontally scalable
• the SQL contention are solved in the DB anyway
• can use Redis instead of celery for example to use things

Queuing

Using always Celery and RabbitMQ for example. If you’re limited in memory it can be a problem with Redis, so better not to use it for this particular task.

Example can be an async task. @task(queue=”event creation”) def on_event_creation(event_id): …

Keep every jobs that need to be moved to a task small.

Object caching

Most of these things are denormalized, we don’t want to use joins and selects for things that are fast.

You need caching when your database can’t handle the load anymore, and only if your data doesn’t change too frequently.

You can expect even worse performances! So it depends a lot on the kind of data.

The right way to cache something is to always save the object in the cache whenever we save and modify (PUSH-only, not PULL-PUSH). There must be a plan on how things should scale.

Redis

redis must fit in memory, you can’t split the data without bringing it down. Getting a list of keys for example blocks everything.

SQL is good, don’t replace it!

SPDY

Perché?

• più grafica
• più velocità
• applicazioni più interattive (angular / ember)

Ancora scrivendo usando HTTP/1.1 per scrivere applicazione (dal ‘99) Django + SPDY

• django
• django-jython
• ..

Function annotation

• small metadata that can be added in the function definition
• PEP 3107 and Python 3.x only def greet(name: str, age: int) -> str:
• rightarrow, nice library that defines a language to define types

Useful libraries

• pyenv
• gorun

Metaclasses

change the behaviour of all the possible objects! Getting a different behaviour from all the classes that subclass object from now on.

class new_object(object): __metaclass__ = DebugMeta

__builtin__.object = new_object

Large scale applications

> 100k lines of code

• easy to write big applications
• faster to write
• no lock-in
• be ahead of the game and react to customer

Typical scenario:

• complex interactions
• complex work concepts

Zeon of application design

• only use objects for everything (and no primitives like dictionaries and tuples)
• different modules should not store any state!
• use a request.context object to carry the information around in the system

Elasticsearch

• query will return what matches and the score about the match
• use a filter unless you really need a query

“multi_match”: …”title^10”, “body” (^10 boost the field title to make it more important)

Using a parent-child relationship to get faster a result from ES.

change the keyboard layout to italian

Continuos integration

• use travis, bamboo or something like this that sets you up well enough out of the box