User Pattern: Button Status

Introduction into User Patterns

Many of you know about Design Patterns of software development, invented to make complicated solutions look less complicated. The problem with Design Patterns is that they describe solutions to coding problems - not for user problem. People abusing Design Patterns tend to align the functionality of application to patterns, sacrificing features users wanted. The application that looks well-designed in the eyes of developers, in fact makes even simple features hard to implement or just takes too much time. As time passes, users become dissatisfied and eventually lose all interest in the product.

People tried to approach the problem from the other end with User Interface Design guidelines. This often made developers unhappy, because their Design Patterns don't explain how to work with web and Ajax application where "business logic" becomes shared between client and server. Developers wanted to see how different frameworks approach this stuff and to make the development process more intuitive. For this reason there should be a way to see how some typical features/functionality are implemented in different frameworks and this should be more detailed than a wiki or a blog in 15 minutes.

So, let me introduce User Patterns. User Pattern is a very abstract story, missing details about design decisions, but detailed enough to provide implementation and see how _simple_, _extensible_ and _maintainable_ this implementation is.

Button Status User Pattern

User story: I want a page with a button and a status field displayed. When I click the button, the status should be updated.

Description: There are five levels in the quest for the implementation of this pattern.
Level 1. The status is blank - it is fetched/calculated only when the button is pressed.
Level 2. The status is initially available - and it is refreshed/calculated when the button is pressed.
Level 3. When refresh/recalculation fails, the error value is displayed in status field.
Level 4. When refresh/recalculation fails, the error value is displayed in status field along with user friendly message in separate field
Level 5. The status value is stored in application database - when the button is pressed, it is recalculated, saved and only when displayed to the user
Level 6. When recalculation/save or fetch operation fails, user should be presented with friendly message explaining the error and further action (i.e. report problem link)

I'm looking forward to create samples for AppEngine webapp, classic Django and Django-nonrel. Feel free to share your snippets.

[PySide] Python for Qt version 1.0.0~beta4 "I have altered the deal" released

I can't see this post on planet.python.org and can't resist to share the good news about new PySide release.

The PySide team is happy to announce the fourth beta release of PySide:
Python for Qt. New versions of some of the PySide toolchain components
apiextractor, generatorrunner, shiboken, libpyside, pyside-tools have been
released as well.

Like the others, this is a source code release only; we hope our community
packagers will be providing provide binary packages shortly. To acquire the
source code packages, refer to our download wiki page [1] or pull the relevant
tagged versions from our git repositories [2].

Major changes since 1.0.0~beta3
===============================

This is a bug fix release. Since beta3, a total of 47 high-priority
bugs have been fixed. See the list of fixed bugs at the end of this message.

Path towards 1.0 release
========================

There are still some outstanding bugs in our Bugzilla [3]. To have these
fixed, we plan to do other beta in two weeks. The beta cycle will continue
until we have all P2 bugs fixed.


About PySide
============

PySide is the Nokia-sponsored Python Qt bindings project, providing
access to not only the complete Qt 4.7 framework but also Qt Mobility,
as well as to generator tools for rapidly generating bindings for any
Qt-based libraries.

The PySide project is developed in the open, with all facilities you'd
expect from any modern OSS project such as all code in a git repository
[2], an open Bugzilla [5] for reporting bugs, and an open design
process [4]. We welcome any contribution without requiring a transfer of
copyright.

List of bugs fixed
==================

624     button click emit doesn't work
484     Error compiling QtContacts 1.1 (problems with const QList)
498     powerStateChanged-SIGNAL not emitted!
509     Can't use Shiboken when both Debug and Released are installed.
528     Connecting to SIGNAL positionUpdated fails
552     Segmentation fault when using QUiLoader and QTabWidget
553     A warning against using QUILoader is needed in the documentation
560     Lack of QtCore.Signal documentation
582     Python slots don't get called when they have a custom decorator
589     Crash related to QGraphicsProxyWidget and QVariant
592     shiboken.dll produces a segmentation fault when reloading a PySide module
608     Photoviewer example missing license boilerplates and shebang lines
609     Python site-packages path cannot be customized
610     QWidgetItemV2 not exposed to Python
626     Problem building PySide on OS X (qabstractfileengine_wrapper.cpp:
No such file or directory)
406     Unable to send instant messages using QMessageService
458     Doesn't build with QtMobility 1.1.0~beta2
487     Support QContactDetailFieldDefinition.setAllowableTypes
497     Miising __lt__ operators in QtMobility::QGeoMapObject
499     QFeedbackHapticsInterface and QFeedbackFileInterface are broken
511     QPainter doesn't respect Qt.NoPen
522     example/threads/mandelbrot.py crashes on exit
523     QWidget.winId() returns PyCObject (expected unsigned long)
530     Importing division from future breaks QPoint division
531     sessionProperty "ConnectInBackground" does not work
539     MCC and MNC interchanged
541     QTableWidget.itemAt(row, col) always returns item at 0, 0.
550     Can't call PySide slot from QtScript when the args are a list of anything.
556     QGraphicsScene.addItem performs very poorly when the scene has >10000 items
562     pyside-uic does not generate some layers properties
568     List insertion time grows with list size
574     In docs of QUuid there's documentation for a function called
"operator QString"
575     Strange behaviour of QTextEdit.ExtraSelection().cursor
584     python pickle module can't treat QByteArray object of PySide
591     QtCore.QRect has no attribute "getRect()" in Windows binary
611     enum values lack a tp_print implementation
614     FAil to register 2 objects in the same address
619     never automatically delete a QWidget that has no parent widget and
is visible
620     QAbstractItemModel.createIndex(int,int,PyObject*) does not
increment refcount
621     QGLWidget.bindTexture(QString) does not bind the texture correctly
622     PPA pyside is broken on Ubuntu 10.10
623     QGLWidget.bindTexture(QPixmap, GLenum, GLenum) is missing
625     QFileDialog return a tuple instead of a unicode
628     pyside-uic can't effect "headerVisible" attribute for QTreeView
and QTreeWidget
232     [FTBFS] Fails to build on hurd-i386 (Test "lock" hangs for more
than 191 minutes)
255     Test qtscripttools_debugger segfaults on ia64
298     Contact subtype not correctly set



References
==========

[1] http://developer.qt.nokia.com/wiki/PySideDownloads
[2] http://qt.gitorious.org/pyside
[3] http://bugs.openbossa.org/
[4] http://www.pyside.org/docs/pseps/psep-0001.html

Thanks
PySide team.

Python GUIniverse

I am on the PySide of the Force.

Injecting SVN bindings into Mercurial on Windows

If you need to add Subversion bindings for your Mercurial, which was installed using ordinary installer (and not TortoiseHg), then the following script can help to put all files in place.

https://bitbucket.org/techtonik/py2exe-relibzip/src/f15f8d032b5b/reinject.py

Unpack svn bindings, add all *.py files from svn/ and libsvn/ directories into the root of library.zip archive *with* these directories. Then call script with path to unpacked libsvn/. The script will generate some *.dll and *.py files in current directory. Put *.py into library.zip:/libsvn/ and *.dll into Mercurial installation directory. You may need to also copy libsvn_swig_py-1.dll into Mercurial dir.

The script can be tuned to insert C extensions to any py2exe distribution compiled with bundle_files=3

Got mail? Part II

See Part I

Validating SSL server certificate with Python 2.x

SSL stands for Secure Sockets Layer and is designed to create secure connection between client and server. Secure means that connection is encrypted and therefore protected from eavesdropping. It also allows to validate site identity when connecting with HTTPS protocol.


However, there is a bug in ssl module from standard library of Python 2.x, that allows successful MITM attack using valid certificate from other site. Basically, module checks when connecting that server certificate is valid and correctly signed by root certificate, but it does not check that certificate actually belongs to the site, i.e. that site name matches the name specified in certificate.


It is still possible to validate server identity in Python 2.6 manually. Let's start with illustration of the vulnerability. The following snippet should fail - it replaces HOST "www.google.com" to connect to with its IP address. If you try to use this IP in Chrome like https://74.125.232.50 - it will show an error, but ssl library will not throw exception.

import socket
import ssl

HOST = "www.google.com"
PORT = 443

# replace HOST name with IP, this should fail connection attempt,
# but it doesn't in Python 2.x
HOST = socket.getaddrinfo(HOST, PORT)[0][4][0]
print(HOST)

# create socket and connect to server
# server address is specified later in connect() method
sock = socket.socket()
sock.connect((HOST, PORT))

# wrap socket to add SSL support
sock = ssl.wrap_socket(sock,
# flag that certificate from the other side of connection is
# required and should be validated when wrapping
cert_reqs=ssl.CERT_REQUIRED,
# file with root certificates
ca_certs="cacert.pem"
)


You will need cacert.pem file with root certificates. Just grab the latest version from http://curl.haxx.se/ca/cacert.pem This code above won't give you any error. Replace HOST value with https://www.debian-administration.org/ to check that certificate validation actually works. This site's certificate is not signed by any root certificates from "cacerts.txt", so you get an error.

To validate that a certificate matches requested site, you need to check commonName field in the subject of the certificate. This information can be accessed with getpeercert() method of wrapped socket.

import socket
import ssl

HOST = "www.google.com"
PORT = 443

# replace HOST name with IP, this should fail connection attempt
HOST = socket.getaddrinfo(HOST, PORT)[0][4][0]
print(HOST)

# create socket and connect to server
# server address is specified later in connect() method
sock = socket.socket()
sock.connect((HOST, PORT))

# wrap socket to add SSL support
sock = ssl.wrap_socket(sock,
# flag that certificate from the other side of connection is
# required and should be validated when wrapping
cert_reqs=ssl.CERT_REQUIRED,
# file with root certificates
ca_certs="cacerts.txt"
)

# manual check of hostname
cert = sock.getpeercert()
for field in cert['subject']:
if field[0][0] == 'commonName':
certhost = field[0][1]
if certhost != HOST:
raise ssl.SSLError(
"Host name '%s' doesn't match certificate host '%s'"
% (HOST, certhost))


That's it. I put my findings to http://wiki.python.org/moin/SSL - you may want check it for updates.

hgsubversion: Installing on Windows

I use Windows primarily, and it's not easy to install Mercurial extensions there if they are not bundled with Mercurial installer itself. I am using plain .msi installer, which doesn't include hgsubversion, so I'll show you how to get this extension in place manually. Suppose you have Mercurial installed into C:\Mercurial Go there and notice library.zip archive. This is where you should add hgsubversion. library.zip has the following structure: / +-- email +-- encodings +-- hgext +-- logging ... __future__.pyc _abcoll.pyc _elementtree.pyd ... zipextimporter.pyc zipfile.pyc Contents of this archive is the whole Mercurial code. Code is written in Python, and is compiled into .pyc and .pyd files for speed and packed into library.zip for convenience. For interpreted languages like Python it is not necessary to compile source files for execution, but they did it. Get latest hgsubversion sources from http://bitbucket.org/durin42/hgsubversion/src by pressing link "get source" in upper right corner. Or download released version from http://pypi.python.org/pypi/hgsubversion/1.1.2 Unpack archive. You should have directory structure like: / +-- hgsubversion +-- notes +-- tests +-- tools .hgignore ... setup.py Now put hgsubversion/ dir from this structure into library.zip archive, inside hgext/ directory, where Mercurial expects to find its extensions. Enable extension by uncommenting line ";hgsubversion =" in Mercurial.ini that is usually located in your profile directory, i.e. C:\Users\yourname If it is not there - copy one from your C:\Mercurial\hgrc.d directory. Try to checkout some subversion repository. You will get an error like this: C:\p>hg clone http://google-twitter.googlecode.com/svn/trunk (falling back to static-http) (falling back to Subversion support) destination directory: trunk abort: subvertpy 0.7.3 or later required, but not found! You need Subversion bindings for Python. They advertise subvertpy, but it is also possible to use official bindings. Those bindings is just a set of libraries that allows Python scripts to use Subversion binary code directly. Unfortunately, after migration to apache.org, Subversion bindings are not compiled anymore, so there is no official place where you can download them. But thanks to http://alagazam.net/ it is possible to get unofficial . Download svn-win32-1.6.12_py.zip or more up-to-date distribution and extract it. You will get a directory structure like: / +-- python +-- libsvn +-- svn README.txt In libsvn/ rename _client.dll to _client.pyd. Do the same with _core.dll, _delta.dll, _ra.dll Maybe you'll have to rename other .dll files, but these were enough for me. Now put svn/ and libsvn/ into the library.zip directly in the root. I also had to copy intl3_svn.dll from an old 1.6.6 installation of SVN into library.zip root (you may find this file in Windows binaries archive from http://alagazam.net/) and place libsvn_swig_py-1.dll from libsvn/ dir also in library.zip root. It should work now.