Peterbe.com

A project I started before Christmas (i.e. about a month ago) is now production ready.

mincss (code on github) is a tool that when given a URL (or multiple URLs) downloads that page and all its CSS and compares each and every selector in the CSS and finds out which ones aren't used. The outcome is a copy of the original CSS but with the selectors not found in the document(s) removed. It goes something like this:

>>> from mincss.processor import Processor
>>> p = Processor()
>>> p.process_url('https://www.peterbe.com')
>>> p.process()
>>> p.inlines
[]
>>> p.links
[<mincss.processor.LinkResult object at 0x10a3bbe50>, <mincss.processor.LinkResult object at 0x10a4d4e90>]
>>> one = p.links[0]
>>> one.href
'//d1ac1bzf3lrf3c.cloudfront.net/static/CACHE/css/c98c3dfc8525.css'
>>> len(one.before)
83108
>>> len(one.after)
10062
>>> one.after[:70]
u'header {display:block}html{font-size:100%;-webkit-text-size-adjust:100'

To whet your appetite, running it on any one of my pages here on my blog it goes from: 82Kb down to 7Kb. Before you say anything; yes I know its because I using a massive (uncustomized) Twitter Bootstrap file that contains all sorts of useful CSS that I'm not using more than 10% of. And yes, those 10% on one page might be different from the 10% on another page and between them it's something like 15%. Add a third page and it's 20% etc. But, because I'm just doing one page at a time, I can be certain it will be enough.

One way of using mincss is to run it on the command line and look at the ouput, then audit it and give yourself an idea of selectors that aren't used. A safer way is to just do one page at a time. It's safer.

The way it works is that it parses the CSS payload (from inline blocks or link tags) with a relatively advanced regular expression and then loops over each selector one at a time and runs it with cssselect (which uses lxml) to see if the selector is used anywhere. If the selector isn't used the selector is removed.

I know I'm not explaining it well so I put together a little example implementation which you can download and run locally just to see how it works.

Now, regarding Javascript and DOM manipulations and stuff; there's not a lot you can do about that. If you know exactly what your Javascript does, for example, creating a div with class loggedin-footer you can prepare your CSS to tell mincss to leave it alone by adding /* no mincss */ somewhere in the block. Again, look at the example implementation for how this can work.

An alternative is to instead of using urllib.urlopen() you could use a headless browser like PhantomJS which will run it with some Javascript rendering but you'll never cover all bases. For example, your page might have something like this:

$(function() {
  $.getJSON('/is-logged-in', function(res) {
    if (res.logged_in) {
      $('<div class="loggedin-footer">').appendTo($('#footer'));
    }
  });
});

But let's not focus on what it can not do.

I think this can be a great tool for all of us who either just download a bloated CSS framework or you have a legacy CSS that hasn't been updated as new HTML is added and removed.

The code is Open Source (of course) and patiently awaiting your pull requests. There's almost full test coverage and there's still work to be done to improve the code such as finding more bugs and optimizing.

Also, there's a rough proxy server you can start that attempts to run it on any URL. You start it like this:

pip install Flask
cd mincss/proxy
python app.py

and then you just visit something like http://localhost:5000/www.peterbe.com/about and you can see it in action. That script needs some love since it's using lxml to render the processed output which does weird things to some DOM elements.

I hope it's of use to you.

UPDATE

Published a blog post about using mincss in action

UPDATE 2

cssmin now supports downloading using PhantomJS which means that Javascript rendering will work. See this announcement

UPDATE 3

Version 0.8 is 500% faster now for large documents. Make sure you upgrade!

So here's my latest little fun side-project: HUGEpic.io http://hugepic.io

It's a web app for uploading massive pictures and looking at them like maps.

The advantages with showing pictures like this are:

• you only download what you need
• you can send a permanent link to a picture at a particular location with a particular zoom level
• you can draw annotations on a layer on top of the image

All the code is here on Github and as you can see it's a Tornado that uses two databases: MongoDB and Redis and when it connects to MongoDB it uses the new Tornado specific driver called Motor which is great.

Here are two perfectly good ways to turn 123456789 into "123,456,789":

import locale

def f1(n):
    locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
    return locale.format('%d', n, True)

def f2(n):
    r = []
    for i, c in enumerate(reversed(str(n))):
        if i and (not (i % 3)):
            r.insert(0, ',')
        r.insert(0, c)
    return ''.join(r)

assert f1(123456789) == '123,456,789'
assert f2(123456789) == '123,456,789'    

Which one do you think is the fastest?

I'm quite fond of hastebin.com. It's fast. It's reliable. And it's got nice keyboard shortcuts that work for my taste.

So, I created a little program to quickly throw things into hastebin. You can have one too:

First create ~/bin/hastebinit and paste in:

#!/usr/bin/python

import urllib2
import os
import json

URL = 'http://hastebin.com/documents'

def run(*args):
    if args:
        content = [open(x).read() for x in args]
        extensions = [os.path.splitext(x)[1] for x in args]
    else:
        content = [sys.stdin.read()]
        extensions = [None]

    for i, each in enumerate(content):
        req = urllib2.Request(URL, each)
        response = urllib2.urlopen(req)
        the_page = response.read()
        key = json.loads(the_page)['key']
        url = "http://hastebin.com/%s" % key
        if extensions[i]:
            url += extensions[i]
        print url


if __name__ == '__main__':
    import sys
    sys.exit(run(*sys.argv[1:]))

Then run: chmod +x ~/bin/hastebinit

Now you can do things like:

$ cat ~/myfile | hastebinit
$ hastebinit < ~/myfile
$ hastebinit ~/myfile myotherfile

Hopefully it'll one day help at least one more soul out there!

In yesterdays DjangoCon BDFL Keynote Adrian Holovaty called out that Django needs a Real-Time story. Well, here's a response to that: django-sockjs-tornado

Immediately after the keynote I went and found a comfortable chair and wrote this app. It's basically a django app that allows you to run a socketserver with manage.py like this:

python manage.py socketserver

Now, you can use all of SockJS to write some really flashy socket apps. In Django! Using Django models and stuff. The example included shows how to write a really simple chat application using Django models. check out the whole demo here

If you're curious about SockJS read the README and here's one of many good threads about the difference between SockJS and socket.io.

The reason I could write this app so quickly was because I have already written a production app using sockjs-tornado so the concepts were familiar. However, this app has (at the time of writing) not been used in any production. So mind you it might still need some more love before you show your mom your django app with WebSockets.

I've finally had time to sort out the django-mongokit code so it's now fully compatible with Django 1.4.

Because I don't personally use the project I've sort of got myself lost in various patches from some awesome contributors who keep it in check.

Also, thanks to Marc Abramowitz who added a tox.ini which I've now updated to also test python 2.7 and Django 1.4

Go forth and build awesome Django apps with MongoKit which is still think is the best wrapper available on PyMongo out there.

Last month I built a very basic mobile app using jQuery Mobile. It's still available here.

One flaw I found with jQuery Mobile is that it's a bit slow. Scrolling up and down feels sluggish. It looks pretty though.
This time around I opted instead to use Twitter Bootstrap instead. (inspired by some other blog post with a similar experience)

Also, with this version I've set up a domain name: uslicensespotter.com
The source code is available here and there are some interesting pieces of this that I'd like to delve into deeper.

Optimization

This new app feels faster and scrolling is smoother. There is still some parts where it doesn't feel snappy. The primary part is when you click one of the buttons. It works something like this:

// binding (simplified)
  $('form a.btn').click(function(event) {
    var $el = $(this);
    var id = $el.attr('id');
    if ($el.hasClass('btn-success')) {
      switch_off($el);
      State.remove(id);
    } else {
      switch_on($el, new Date());
      State.add(id);
    }
    return false;
  });


// the switch_on function
  function switch_on($el, timestamp) {
    $el.addClass('btn-success');
    $('i', $el).addClass('icon-white').removeClass('icon-remove').addClass('icon-check');
    $('span', $el).text(timeSince(timestamp));
  }

There are two potentials for making this faster.

1. Instead of using element.click(...) I can use touch events which supposedly fire better thus starting the actual animation earlier.
2. Instead of modifying the element (adding a class, adding a class, removing a class, adding a class, changing the text) what I could do is to remove the element from the DOM, manipulate it and then re-insert it back into the DOM. That way the (mobile) browser doesn't have to re-render after each manipulation.

My next task is to apply both of these ideas and try to somehow keep and eye on which makes the biggest impact.

Deployment

One neat new feature with this new code is the deployment script, build.py. The actual code might be a bit of a mess but the way it works for me is great.

What I do is that I work on the app by editing dev.html and when I deploy I run python build.py and it opens dev.html and concatenates and minifies all CSS and Javascript ready for ideal caching. This reduces the static assets down to just three files weighing only 78Kb altogether.

(Note: even more can be done such as switching to ZeptoJS and removing bootstrap stuff I don't need with a custom download)

What the script does is that it parses the dev.html template with lxml and applies whatever transformations it needs to do such as generating the Apple touch images eg. this one

I think a lot of mobile web developers can benefit from this script. Maybe you don't want to copy it verbatim but you might want to copy it and do the transformations you want to do.

(This post is a response to Richard Patchet's request for tips on how to actually use premailer)

First of all, premailer is a Python library that converts a document of HTML and tranforms its <style> tags into inline style attributes on the HTML itself. This comes very handy when you need to take a nicely formatted HTML newletter template and prepare it before sending because when you send HTML emails you can't reference an external .css file.

So, here's how to turn it into a command line script.

First, install, then write the script:

$ pip install premailer
$ touch ~/bin/run-premailer.py
$ chmod +x ~/bin/run-premailer.py

Now, you might want to do this differently but this should get you places:

#!/usr/bin/env python

from premailer import transform

def run(files):
    try:
        base_url = [x for x in files if x.count('://')][0]
        files.remove(base_url)
    except IndexError:
        base_url = None

    for file_ in files:
        html = open(file_).read()
        print transform(html, base_url=base_url)

if __name__ == '__main__':
    import sys
    run(sys.argv[1:])

To test it, I've made a sample HTML page that looks like this:

<html>
    <head>
        <title>Test</title>
        <style>
        h1, h2 { color:red; }
        strong {
          text-decoration:none
          }
        p { font-size:2px }
        p.footer { font-size: 1px}
        p a:link { color: blue; }
        </style>
    </head>
    <body>
        <h1>Hi!</h1>
        <p><strong>Yes!</strong></p>
        <p class="footer" style="color:red">Feetnuts</p>
        <p><a href="page2/">Go to page 2</a></p>
    </body>
</html>

Cool. So let's run it: $ run-premailer.py test.html

<html>
  <head>
    <title>Test</title>
  </head>
  <body>
        <h1 style="color:red">Hi!</h1>
        <p style="font-size:2px"><strong style="text-decoration:none">Yes!</strong></p>
        <p style="{color:red; font-size:1px} :link{color:red}">Feetnuts</p>
    <p style="font-size:2px"><a href="page2/" style=":link{color:blue}">Go to page 2</a></p>
    </body>
</html>

Note that premailer supports converting relative URLs, so let's actually using that:
$ run-premailer.py test.html https://www.peterbe.com

<html>
  <head>
    <title>Test</title>
  </head>
  <body>
        <h1 style="color:red">Hi!</h1>
        <p style="font-size:2px"><strong style="text-decoration:none">Yes!</strong></p>
        <p style="{color:red; font-size:1px} :link{color:red}">Feetnuts</p>
    <p style="font-size:2px"><a href="https://www.peterbe.com/page2/" 
     style=":link{color:blue}">Go to page 2</a></p>
    </body>
</html>

I'm sure you can think of many many ways to improve that. Mayhaps use argparse or something fancy to allow for more options. Mayhaps make it so that you can supply named .css files on the command line that get automagically inserted on the fly.

This is part 1 in, hopefully, a series of blog articles about developing mobile apps with Javascript.

My app that I'm going to build is called "US License Plate Spotter". A dead-simple app where you tick off each US state once you see it.

In case you didn't know, in the USA, you mostly see "local" license plates because if you for example buy a car in Micigan but move to California, after about 3 months you have to re-license it with plates from the state you're living in. So here where I live, in California, you mostly see "California plates" but every now and then you see other plates such as Nevada, Washington or Floria. The further away, the less likely to be spotted.

Anyway, the first version is available right here: https://www.peterbe.com/uslicenseplates/index.html Code is on Github
It works best in smartphones like an Android or iOS app since it's built with jQuery Mobile

This is about 2 hours of work which is pretty quick but it was easy because I've used jQuery Mobile a lot in the past and this was more or less just getting familiar with the recent changes.
The app works fine and I even used it this last weekend to keep track of new license plates since Friday.

Next steps:

1. Polish it a bit more with an icon, an about page and maybe add the date it was spotted
2. Add "cloud storage" (at the moment it uses localStorage) using the Facebook API
3. Compile an Android and iOS version with PhoneGap and see if I can launch it in some app stores.

UPDATE

Here's part 2 in the series.

The @staticmethod decorator is nothing new. In fact, it was added in version 2.2. However, it's not till now in 2012 that I have genuinely fallen in love with it.

First a quick recap to remind you how @staticmethod works.

class Printer(object):

    def __init__(self, text):
        self.text = text

    @staticmethod
    def newlines(s):
        return s.replace('\n','\r')

    def printer(self):
        return self.newlines(self.text)

p = Printer('\n\r')
assert p.printer() == '\r\r'

So, it's a function that has nothing to do with the instance but still belongs to the class. It belongs to the class from an structural point of view of the observer. Like, clearly the newlines function is related to the Printer class. The alternative is:

def newlines(s):
    return s.replace('\n','\r')

class Printer(object):

    def __init__(self, text):
        self.text = text

    def printer(self):
        return newlines(self.text)

p = Printer('\n\r')
assert p.printer() == '\r\r'

It's the exact same thing and one could argue that the function has nothing to do with the Printer class. But ask yourself (by looking at your code); how many times do you have classes with methods on them that take self as a parameter but never actually use it?

So, now for the trump card that makes it worth the effort of making it a staticmethod: object orientation. How would you do this neatly without OO?

class UNIXPrinter(Printer):

    @staticmethod
    def newlines(s):
        return s.replace('\n\r', '\n')

p = UNIXPrinter('\n\r')
assert p.printer() == '\n'  

Can you see it? It's ideal for little functions that should be domesticated by the class but have nothing to do with the instance (e.g. self). I used to think it looked like it's making a pure looking thing like something more complex that it needs to be. But now, I think it looks great!