Validating user objects with Cerberus

People keep telling me that they want to validate class and instance attributes (object properties) with Cerberus. While it certainly wasn’t conceived with that goal in mind, it is actually very possible to leverage both the Python data model and Cerberus extensibility to achieve object validation. Nuts & Bolts Let’s say that we have a simple class: >>> class Person(object): ... pass We create a Person instance and add a few properties and values: »

Introducing Eve.NET the HTTP/REST Client for Humans™

Eve.NET is a simple HTTP and REST client for Web Services powered by the Eve Framework. It leverages both System.Net.HttpClient and Json.NET to provide the best possible Eve experience on the .NET platform.

Written and maintained by the same author of the Eve Framework itself, Eve.NET is delivered as a portable library (PCL) and runs seamlessly on .NET4, Mono, Xamarin.iOS, Xamarin.Android, Windows Phone 8 and Windows 8. We use Eve.NET internally to power our iOS, Web and Windows applications.

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Open Source and Code Responsibility

Last week I was speaking at an Open Source panel at Better Software 2014, and one of the topics that we touched was code responsibility. This is an important topic for anyone who is maintaining an open source project, especially when it comes to the process of reviewing and accepting code contributions.

At some point during the debate, I argued that when a maintainer merges a pull request, he (or she) implicitly agrees on being responsible for that code. That seemed to strike some surprise into most attendees.

Yes, in theory any contributor is just a ping away so in case trouble arises one can always reach him, or her. Unfortunately this is not always the case. While some contributors will fully embrace your project and keep helping after their initial contribution, truth is that a good number of them will just move on, never to be seen again.

There’s nothing wrong with that. Not everyone has spare time to devote to your project, which is perfectly fine. It is natural for most people to contribute what they need to a project and then go on their way. Actually, one could argue that most projects grow and prosper precisely thanks to this kind of contributions.

However this attitude can become an incumbent when big chunks of code get merged, usually as new (big) features. Good practices advice against merging huge pull requests. In fact they are rare and when they do come, it is a good idea to ask for them to be split into smaller ones. But no matter the format, a huge contribution is likely to hit a project one day or another. It might even come from more than one person: a disconnected and distributed team of contributors who have been patiently tinkering on a side branch or a fork for example. When this happens, and provided that the contribution is worth merging, the maintainer should then ask him/herself the obvious question: am I willing to deal with the consequences of this merge?

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Feature Overview: The Eve OpLog

The operations log or OpLog is a new Eve feature that I’m currently developing on the oplog experimental branch. It’s supposed to help in addressing a subtle issue that we’ve been dealing with, but I believe it can also emerge as a very useful all-around tool. I am posting about it in the hope of gathering some feedback from Eve contributors and users, so that I can better pinpoint design and implementation before I merge it to the main development branch.

What is the OpLog?

The OpLog is a special resource that keeps a record of operations that modify the data stored by the API. Every POST, PATCH, PUT and DELETE operation can eventually be recorded by the oplog.

At its core the oplog is simply a server log, something that’s always been on the Eve roadmap. What makes it a little bit different is its ability to be exposed as a read-only API endpoint. This would in turn allow clients to query it as they would with any other standard endpoint.

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Ordered Dictionaries with Python 2.4-2.6

OrderedDict is a super handy data structure.

An OrderedDict is a dict that remembers the order that keys were first inserted. If a new entry overwrites an existing entry, the original insertion position is left unchanged. Deleting an entry and reinserting it will move it to the end.

Problem is, this stuff is only available in the standard library since Python 2.7 while my project also needs to support Python 2.6. Fortunately there’s a back-port available and it is only a pip install away:

# make OrderedDict available on Python 2.6-2.4
$ pip install ordereddict

ordereddict is based on the awesome recipe by Raymond Hettinger, works with Python 2.4-2.6 and, most importantly, is a drop-in replacement for OrderedDict.

However if you want your code to run seamlessly on all Pythons there’s still some work to be done. First of all you want to make sure that the appropriate OrderedDict is imported, either the standard library version (for Python 2.7 and above) or the back-port release.

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Author image Nicola Iarocci on #python,

Eve 0.4 and Cerberus 0.7 Released

Eve 0.4 adds cool features like Document Versioning and Coherence Mode. Cerberus 0.7 allows regex validation amongst other niceties. Make sure to check the official v0.4 announcement for all the details. »

10 Most Common Python Mistakes

Python’s simple, easy-to-learn syntax can mislead Python developers – especially those who are newer to the language – into missing some of its subtleties and underestimating the power of the language. With that in mind, this article presents a “top 10” list of somewhat subtle, harder-to-catch mistakes that can bite even the most advanced Python developer in the rear. via 10 Most Common Python Mistakes. »

Author image Nicola Iarocci on #python,

Eve 0.3 Released

Today we released Eve v0.3. It includes customizable Files Storage support (on GridFS by default), a lot of fixes, several breaking changes and a lot of love. Head over to relevant blog post and/or to changelog to know more about it. »

REST APIs for Humans at FOSDEM

Yesterday I gave a talk at FOSDEM 2014 in Brussels. The conference itself was amazing, with over 5000 attendees literally swarming and taking over the ULB Campus. I was stoked at how smoothly everything was going on despite the incredible number of simultaneous sessions and the number of attendees continuously flowing between buildings and conference rooms. Everybody involved, volunteers and attendees, has been very welcoming, charming and helpful. In short, I had a blast. »

Python and Flask Are Ridiculously Powerful

As a developer, I sometimes forget the power I yield. It’s easy to forget that, when something doesn’t work the way I’d like, I have the power to change it. via Python and Flask Are Ridiculously Powerful. »

Python is the Language of the Year

We shouldn’t really trust this kind of statistics, I know, but when my favorite language comes out as a clear winner, I can’t resist and take them for good. Python is the “language of the year” according to the PYPL index : it had the biggest increase in popularity share in 2013. PHP had the biggest decline. Meanwhile, Java continues to have the highest popularity share among the programming languages. »

Author image Nicola Iarocci on #python,

Alex Gaynor — About Python 3

A very interesting read if you’re into Python. Eve has been Python 3 compatible for a while and honestl, I would be surprised to find that somebody is running it in production under Python 3. Why aren’t people using Python 3? First, I think it’s because of a lack of urgency. Many years ago, before I knew how to program, the decision to have Python 3 releases live in parallel to Python 2 releases was made. »

Author image Nicola Iarocci on #python,

You Should Change Your Python Shell

If you write Python code, switching to IPython is the number one thing you can do to immediately improve your productivity. Bold words, I know. Let’s look at how IPython can make you a more productive programmer. via You Should Change Your Python Shell | GrokCode. »

Author image Nicola Iarocci on #python,

Eve v0.0.8 has been released

Most significant features are probably the native support for MongoDB write concern settings, new event hooks allowing for transformation of documents before they are sent to clients, increased handling of both pagination and CORS, and the native validation of float data types. Get it on PyPI, go straight to the source code or more likely, visit the project homepage. »

Champion Pythonista

La Open Source Report Card è un’iniziativa divertente. E’ difficile resistere al richiamo dell’ego… soprattutto quand’è smisurato. Nicola is a champion Pythonista (one of the top 11% most active Python users) who loves pushing code. Nicola is a nine-to-fiver who seems to work best in the mid-afternoon. »

Multi-threading in Python

Multithreaded Python Tutorial with the “Threadworms” Demo è un’ottima guida introduttiva ai thread ed alla programmazione multithread in Python. Dalla teoria alla pratica, in pochi minuti si arriva a creare una variante multithread di Snake. »

Gestione degli Eventi in Python

Gli eventi sono molto usati nelle GUI e nelle implementazioni del modello MVC (Model, View, Controller). Un’altra applicazione tipica è nei protocolli di comunicazione, laddove layer di basso livello devono informare quelli più alti quando ci sono dati in ingresso o in uscita.

Il linguaggio C# dispone da sempre di una soluzione elegante al problema della gestione degli eventi: il delegato EventHandler. Events è una mia implementazione Python del EventHandler C#. In pratica si tratta di una classe molto leggera che incapsula il cuore del meccanismo di sottoscrizione e gestione degli eventi, e tenta di farlo in maniera “naturale”, sembrando parte integrante del linguaggio Python.

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Vi presento Eve il framework per le REST API Web

Lo scorso anno abbiamo lavorato duro per costruirci una RESTful Web API su misura, flessibile e completa. In corso d’opera abbiamo imparato molto sulle migliori pratiche REST, mettendo anche alla frusta le rinomate capacità Web del linguaggio Python. Ad EuroPython 2012 ho poi raccontato la nostra esperienza e condiviso ciò che avevamo imparato. In quell’occasione mi sono reso conto di quanto l’argomento fosse d’attualità, tanto che da quel 4 luglio le slide che avevo preparato (le trovate su Speaker Deck o Slideshare) ed i video su YouTube (italiano; inglese) hanno totalizzato 30mila visite. »

Cerberus 0.0.2: tipi di dato personalizzati

Primo aggiornamento per Cerberus, lo strumento per la convalida dei dizionari Python che ho rilasciato qualche tempo fa. Ora è possibile estendere la lista dei tipi di dato da convalidare, aggiungendone di propri. Per esempio nella nostra REST API (che usa Cerberus per la validazione) uso questa tecnica per implementare e convalidare il tipo ObjectId, tipico di MongoDB. I dettagli li trovate nella documentazione. »