Skip to main content

Ralsina.Me — Roberto Alsina's website

Posts about qt (old posts, page 12)

How much web browser can you put in 128 lines of code?

UP­DATE: If you read this and all you can say is "o­h, he's just em­bed­ding We­bKit", I have two things to tell you:

  1. Duh! Of course the 128 lines don't in­­­clude the ren­der­ing en­gine, or the TCP im­­ple­­men­­ta­­tion, or the GUI tool­k­it. This is about the rest of the browser, the part around the web ren­der­ing en­gine. You know, just like Aro­ra, Rekon­q, Epiphany, and ev­ery­one else that em­beds we­bkit or mozil­la does it? If you did­n't get that be­­fore this ex­­pla­­na­­tion... facepalm.

  2. Get your favourite we­bkit fork and try to do this much with the same amount of code. I dare you! I dou­ble dog dare you!

Now back to the orig­i­nal ar­ti­cle


To­day, be­cause of a IRC chat, I tried to find a 42-­line web brows­er I had writ­ten a while ago. Sad­ly, the paste­bin where I post­ed it was dead, so I learned a lesson: It's not a good idea to trust a paste­bin as code repos­i­to­ry

What I liked about that 42-­line brows­er was that it was not the typ­i­cal ex­am­ple, where some­one dumps a We­bkit view in a win­dow, loads a page and tries to con­vince you he's cool. That one is on­ly 7 lines of code:

import sys
from PyQt4 import QtGui,QtCore,QtWebKit
app=QtGui.QApplication(sys.argv)
wb=QtWebKit.QWebView()
wb.setUrl(QtCore.QUrl('http://www.python.org'))
wb.show()
sys.exit(app.exec_())

And if I want­ed to make the code uglier, it could be done in 6.

But any­way, that 42-­line brows­er ac­tu­al­ly looked use­ful!

This 42-line web browser, courtesy of #python and #qt -- http... on Twitpic

Those but­tons you see ac­tu­al­ly worked cor­rect­ly, en­abling and dis­abling at the right mo­men­t, the URL en­try changed when you clicked on links, and some oth­er bit­s.

So, I have de­cid­ed to start a smal­l, in­ter­mit­tent project of code golf: put as much brows­er as I can in 128 lines of code (not count­ing com­ments or blanks), start­ing with PyQt4.

This has a use­ful pur­pose: I al­ways sus­pect­ed that if you as­sumed PyQt was part of the base sys­tem, most apps would fit in flop­pies again. This one fits on a 1.44MB flop­py some 500 times (so you could use 360KB com­modore flop­pies if you prefer­!).

So far, I am at about 50 lines, and it has the fol­low­ing fea­tures:

  • Zoom in (C­tr­l++)

  • Zoom out (C­tr­l+-)

  • Re­set Zoom (C­tr­l+=)

  • Find (C­tr­l+F)

  • Hide find (Esc)

  • But­­tons for back­­/­­for­ward and reload

  • URL en­try that match­es the page + au­­to­­com­­plete from his­­to­ry + smart en­try (adds http://, that kind of thing)

  • Plug­ins sup­­port (in­­clud­ing flash)

  • The win­­dow ti­­tle shows the page ti­­tle (with­­out brows­er ad­ver­tis­ing ;-)

  • Progress bar for page load­­ing

  • Sta­­tus­bar that shows hov­­ered links URL

  • Takes a URL on the com­­mand line, or opens http://python.org

  • Mul­ti­­plat­­form (works in any place QtWe­bKit work­s)

Miss­ing are tabs and proxy sup­port. I ex­pect those will take an­oth­er 40 lines or so, but I think it's prob­a­bly the most fea­ture­ful of these toy browser­s.

The code... it's not all that hard. I am us­ing lamb­da a lot, and I am us­ing PyQt's key­word ar­gu­ments for sig­nal con­nec­tion which makes lines long, but not hard. It could be made much small­er!

Here it is in ac­tion:

And here's the code:

#!/usr/bin/env python
"A web browser that will never exceed 128 lines of code. (not counting blanks)"

import sys
from PyQt4 import QtGui,QtCore,QtWebKit

class MainWindow(QtGui.QMainWindow):
    def __init__(self, url):
        QtGui.QMainWindow.__init__(self)
        self.sb=self.statusBar()

        self.pbar = QtGui.QProgressBar()
        self.pbar.setMaximumWidth(120)
        self.wb=QtWebKit.QWebView(loadProgress = self.pbar.setValue, loadFinished = self.pbar.hide, loadStarted = self.pbar.show, titleChanged = self.setWindowTitle)
        self.setCentralWidget(self.wb)

        self.tb=self.addToolBar("Main Toolbar")
        for a in (QtWebKit.QWebPage.Back, QtWebKit.QWebPage.Forward, QtWebKit.QWebPage.Reload):
            self.tb.addAction(self.wb.pageAction(a))

        self.url = QtGui.QLineEdit(returnPressed = lambda:self.wb.setUrl(QtCore.QUrl.fromUserInput(self.url.text())))
        self.tb.addWidget(self.url)

        self.wb.urlChanged.connect(lambda u: self.url.setText(u.toString()))
        self.wb.urlChanged.connect(lambda: self.url.setCompleter(QtGui.QCompleter(QtCore.QStringList([QtCore.QString(i.url().toString()) for i in self.wb.history().items()]), caseSensitivity = QtCore.Qt.CaseInsensitive)))

        self.wb.statusBarMessage.connect(self.sb.showMessage)
        self.wb.page().linkHovered.connect(lambda l: self.sb.showMessage(l, 3000))

        self.search = QtGui.QLineEdit(returnPressed = lambda: self.wb.findText(self.search.text()))
        self.search.hide()
        self.showSearch = QtGui.QShortcut("Ctrl+F", self, activated = lambda: (self.search.show() , self.search.setFocus()))
        self.hideSearch = QtGui.QShortcut("Esc", self, activated = lambda: (self.search.hide(), self.wb.setFocus()))

        self.quit = QtGui.QShortcut("Ctrl+Q", self, activated = self.close)
        self.zoomIn = QtGui.QShortcut("Ctrl++", self, activated = lambda: self.wb.setZoomFactor(self.wb.zoomFactor()+.2))
        self.zoomOut = QtGui.QShortcut("Ctrl+-", self, activated = lambda: self.wb.setZoomFactor(self.wb.zoomFactor()-.2))
        self.zoomOne = QtGui.QShortcut("Ctrl+=", self, activated = lambda: self.wb.setZoomFactor(1))
        self.wb.settings().setAttribute(QtWebKit.QWebSettings.PluginsEnabled, True)

        self.sb.addPermanentWidget(self.search)
        self.sb.addPermanentWidget(self.pbar)
        self.wb.load(url)


if __name__ == "__main__":
    app=QtGui.QApplication(sys.argv)
    if len(sys.argv) > 1:
        url = QtCore.QUrl.fromUserInput(sys.argv[1])
    else:
        url = QtCore.QUrl('http://www.python.org')
    wb=MainWindow(url)
    wb.show()
    sys.exit(app.exec_())

Charla: aplicaciones extensibles con PyQt

Span­ish on­ly, since it's about a video in span­ish ;-)

Acá es­tá, gra­cias a la gente de Junín, un video de mi char­la "Apli­ca­ciones ex­ten­si­bles us­an­do PyQt", en la que in­ten­to mostrar co­mo de­sar­rol­lar una apli­cación con PyQt y yap­sy.

No es una char­la con la que es­té muy con­tento. La otra sal­ió mejor, pero no se filmó, así que quedará so­lo en la memo­ria de los cu­a­tro gatos lo­cos que es­tábamos ahí ;-)

El resto de las char­las: http://un­no­ba.blip.tv/

Making your app modular: Yapsy

That a plug­in ar­chi­tec­ture for a com­plex app is a good idea is one of those things that most peo­ple kin­da agree on. One thing we don't quite agree is how the heck are we go­ing to make out app mod­u­lar?

One way to do it (if you are cod­ing python) is us­ing Yap­sy.

Yap­sy is awe­some. Al­so, yap­sy is a bit un­der­doc­u­ment­ed. Let's see if this post fix­es that a bit and leaves just the awe­some.

Up­date: I had not seen the new Yap­sy doc­s, re­leased a few days ago. They are much bet­ter than what was there be­fore :-)

Here's the gen­er­al idea be­hind yap­sy:

  • You cre­ate a Plug­in Man­ag­er that can find and load plug­ins from a list of places (for ex­am­­ple, from ["/us­r/share/ap­p­­name/­­plu­g­in­s", "~/.ap­p­­name/­­plu­g­in­s"]).

  • A plug­in cat­e­­go­ry is a class.

  • There is a map­ping be­tween cat­e­­go­ry names and cat­e­­go­ry class­es.

  • A plug­in is a mod­­ule and a meta­­da­­ta file. The mod­­ule de­fines a class that in­­her­its from a cat­e­­go­ry class, and be­­longs to that cat­e­­go­ry.

    The meta­­da­­ta file has stuff like the plug­in's name, de­scrip­­tion, URL, ver­­sion, etc.

One of the great things about Yap­sy is that it does­n't spec­i­fy too much. A plug­in will be just a python ob­jec­t, you can put what­ev­er you want there, or you can nar­row it down by spec­i­fy­ing the cat­e­go­ry class.

In fac­t, the way I have been do­ing the cat­e­go­ry class­es is:

  • Start with an em­p­­ty class

  • Im­­ple­­ment two plug­ins of that cat­e­­go­ry

  • If there is a chunk that's much alike in both, move it in­­­to the cat­e­­go­ry class.

But trust me, this will all be clear­er with an ex­am­ple :-)

I will be do­ing it with a graph­i­cal PyQt ap­p, but Yap­sy works just as well for head­less of CLI app­s.

Let's start with a sim­ple ap­p: an HTML ed­i­tor with a pre­view wid­get.

//ralsina.me/static/yapsy/editor1.jpeg

A sim­ple ed­i­tor with pre­view

Here's the code for the ap­p, which is re­al­ly sim­ple (it does­n't save or do any­thing, re­al­ly, it's just an ex­am­ple):

ed­i­tor1.py

from PyQt4 import QtCore, QtGui, QtWebKit
import os, sys

class Main(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.layout = QtGui.QVBoxLayout()
        self.editor = QtGui.QPlainTextEdit()
        self.preview = QtWebKit.QWebView()
        self.layout.addWidget(self.editor)
        self.layout.addWidget(self.preview)
        self.editor.textChanged.connect(self.updatePreview)
        self.setLayout(self.layout)

    def updatePreview(self):
        self.preview.setHtml(self.editor.toPlainText())

def main():
    # Again, this is boilerplate, it's going to be the same on
    # almost every app you write
    app = QtGui.QApplication(sys.argv)
    window=Main()
    window.show()
    # It's exec_ because exec is a reserved word in Python
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Note

From now on list­ings will not in­clude the main func­tion, be­cause it nev­er changes.

But this ap­pli­ca­tion has an ob­vi­ous lim­it: you have to type HTML in it. Why not type python code in it and have it con­vert to HTML for dis­play? Or Wi­ki markup, or re­struc­tured tex­t?

You could, in prin­ci­ple, just im­ple­ment all those mod­es, but then you are as­sum­ing the re­spon­s­abil­i­ty of sup­port­ing ev­ery thing-that-­can-be-­turned-in­to-HTM­L. Your app would be a mono­lith. That's where yap­sy en­ters the scene.

So, let's cre­ate a plug­in cat­e­go­ry, called "For­mat­ter" which takes plain text and re­turns HTM­L. Then we add stuff in the UI so the us­er can choose what for­mat­ter he wants, and im­ple­ment two of those.

Here's our plug­in cat­e­go­ry class:

cat­e­gories.py

class Formatter(object):
    """Plugins of this class convert plain text to HTML"""

    name = "No Format"

    def formatText(self, text):
        """Takes plain text, returns HTML"""
        return text

Of course what good is a plug­in ar­chi­tec­ture with­out any plug­ins for it? So, let's cre­ate two plug­ins.

First: a plug­in that takes python code and re­turns HTM­L, thanks to pyg­ments.

plu­g­in­s/pyg­men­tize.py

from pygments import highlight
from pygments.lexers import PythonLexer
from pygments.formatters import HtmlFormatter

from categories import Formatter

class Pygmentizer(Formatter):
    name = "Python Code"

    def formatText(self, text):
        return highlight(text, PythonLexer(), HtmlFormatter(full=True))

See how it goes in­to a plug­ins fold­er? Lat­er on we will tell yap­sy to search there for plug­ins.

To be rec­og­nized as a plug­in, it needs a meta­da­ta file, too:

plu­g­in­s/pyg­men­tize.yap­sy-­plu­g­in

[Core]
Name = Python Code
Module = pygmentize

[Documentation]
Author = Roberto Alsina
Version = 0.1
Website = //ralsina.me
Description = Highlights Python Code

And re­al­ly, that's all there is to mak­ing a plug­in. Here's an­oth­er one for com­par­ison, which us­es do­cu­tils to for­mat re­Struc­tured Tex­t:

plu­g­in­s/rest.py

from categories import Formatter
import docutils.core
import docutils.io


class Rest(Formatter):
    name = "Restructured Text"

    def formatText(self, text):
        output = docutils.core.publish_string(
            text, writer_name = 'html'
        )
        return output

plu­g­in­s/rest.yap­sy-­plu­g­in

[Core]
Name = Restructured Text
Module = rest

[Documentation]
Author = Roberto Alsina
Version = 0.1
Website = //ralsina.me
Description = Formats restructured text

And here they are in ac­tion:

//ralsina.me/static/yapsy/editor2.jpeg

reSt mode

//ralsina.me/static/yapsy/editor3.jpeg

Python mode

Of course us­ing cat­e­gories you can do things like a "Tool­s" cat­e­go­ry, where the plug­ins get added to a Tools menu, too.

And here's the ap­pli­ca­tion code:

ed­i­tor2.py

from categories import Formatter
from yapsy.PluginManager import PluginManager

class Main(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.layout = QtGui.QVBoxLayout()
        self.formattersCombo = QtGui.QComboBox()
        self.editor = QtGui.QPlainTextEdit()
        self.preview = QtWebKit.QWebView()

        self.layout.addWidget(self.formattersCombo)
        self.layout.addWidget(self.editor)
        self.layout.addWidget(self.preview)

        self.editor.textChanged.connect(self.updatePreview)
        self.setLayout(self.layout)

        # Create plugin manager
        self.manager = PluginManager(categories_filter={ "Formatters": Formatter})
        self.manager.setPluginPlaces(["plugins"])

        # Load plugins
        self.manager.locatePlugins()
        self.manager.loadPlugins()

        # A do-nothing formatter by default
        self.formattersCombo.addItem("None")
        self.formatters = {}
        print self.manager.getPluginsOfCategory("Formatters")
        for plugin in self.manager.getPluginsOfCategory("Formatters"):
            print  "XXX"
            # plugin.plugin_object is an instance of the plugin
            self.formattersCombo.addItem(plugin.plugin_object.name)
            self.formatters[plugin.plugin_object.name] = plugin.plugin_object

    def updatePreview(self):
        # Check what the current formatter is
        name =  unicode(self.formattersCombo.currentText())
        text = unicode(self.editor.toPlainText())
        if name in self.formatters:
            text = self.formatters[name].formatText(text)
        self.preview.setHtml(text)

In short: this is easy to do, and it leads to fix­ing your ap­pli­ca­tion's in­ter­nal struc­ture, so it helps you write bet­ter code.

Full source code for ev­ery­thing.

eBooks and PyQt: a good match

I have been putting lots of love in­to Aran­du­ka an eBook man­ager, (which is look­ing very good late­ly, thanks!), and I did­n't want it to al­so be an eBook read­er.

But then I thought... how hard can it be to read ePub? Well, it's freak­ing easy!

Here's a good start at stack­over­flow.­com but the short of it is... it's a zip with some XML in it.

One of those XML files tells you where things are, one of them is the TOC, the rest is just a small stat­ic col­lec­tion of HTM­L/C­SS/im­ages.

So, here are the in­gre­di­ents to rol­l-y­our-own ePub read­er wid­get in 150 LOC:

  • Use python's zip­­file li­brary to avoid ex­­plod­ing the zip (that's lame)

  • Use El­e­­ment Tree to parse said XML files.

  • Use PyQt's QtWe­bKit to dis­­­play said col­lec­­tion of XM­L/C­SS/Im­ages

  • Use this recipe to make QtWe­bKit tell you when it wants some­thing from the zip­­file.

Plug some things to oth­er­s, shake vig­or­ous­ly, and you end up with this:

Share photos on twitter with Twitpic

Here's the code (as of to­day) and the UI file you need.

Miss­ing stuff:

  • It does­n't dis­­­play the cov­­er.

  • It on­­ly shows the top lev­­el of the ta­ble of con­­tents.

  • I on­­ly test­ed it on two books ;-)

  • It sure can use a lot of refac­­tor­ing!

Nei­ther should be ter­ri­bly hard to do.

Very pythonic progress dialogs.

Sometimes, you see a piece of code and it just feels right. Here's an example I found when doing my "Import Antigravity" session for PyDay Buenos Aires: the progressbar module.

Here's an example that will teach you enough to use progressbar effectively:

progress = ProgressBar()
for i in progress(range(80)):
    time.sleep(0.01)

Yes, that's it, you will get a nice ASCII progress bar that goes across the ter­mi­nal, sup­ports re­siz­ing and moves as you it­er­ate from 0 to 79.

The progressbar module even lets you do fancier things like ETA or fie transfer speeds, all just as nicely.

Is­n't that code just right? You want a progress bar for that loop? Wrap it and you have one! And of course since I am a PyQt pro­gram­mer, how could I make PyQt have some­thing as right as that?

Here'show the out­put looks like:

progress

You can do this with ev­ery toolk­it, and you prob­a­bly should!. It has one ex­tra fea­ture: you can in­ter­rupt the it­er­a­tion. Here's the (short) code:

# -*- coding: utf-8 -*-
import sys, time
from PyQt4 import QtCore, QtGui

def progress(data, *args):
    it=iter(data)
    widget = QtGui.QProgressDialog(*args+(0,it.__length_hint__()))
    c=0
    for v in it:
        QtCore.QCoreApplication.instance().processEvents()
        if widget.wasCanceled():
            raise StopIteration
        c+=1
        widget.setValue(c)
        yield(v)

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)

    # Do something slow
    for x in progress(xrange(50),"Show Progress", "Stop the madness!"):
        time.sleep(.2)

Have fun!


Contents © 2000-2020 Roberto Alsina