A conversion guide for the new QGIS API

pyqgis-sip2.rst

The QVariant type doesn't exsits any more so any methods returning QVariant will be auto converted to Python types. You no longer need to convert the return type using the toXXXX methods.

Remove all:

toString()
toList()
toInt()
toStringList()
toByteArray()
QVariant(..)
QString(...)

Set QSettings return type

More info: http://pyqt.sourceforge.net/Docs/PyQt4/pyqt_qsettings.html

Before:

settings.value(“/yourboolsetting”, True).toBool()
settings.value(“/yourintsetting”, 10).toInt()[0]
settings.value(“/yourintsetting”).toByteArray()

After:

settings.value(“/yourboolsetting”, True, type=bool)
settings.value(“/yourintsetting”, 10, type=int)
settings.value(“/yourintsetting”, QByteArray(), type=QByteArray)

Replace QString methods

QString no longer exits in the new QGIS API. Any methods that return a QString will be converted into a native Python str. All QString methods need to be replaced with native string methods.

Before:

yourstring.right(4)
files.join(",")
if yourstring.length() > 4:
if yourstring.isEmpty()

After:

yourstring[4:]
",".join(files)
if len(yourstring) > 4
if not yourstring

Replace QStringList with list

Before:

mystrings = QStringList()

After:

mystrings = []

Remove QVariant calls

The QVariant also doesn't exsits any more so any methods returning QVariant will be auto converted to Python types. However QVariant can still be used to access it's emun values e.g. QVariant.Int can set be used.

Before:

myvalue = QVariant(10)
myvalue = QVariant("Hello World")

After:

myvalue = 10
myvalue = "Hello World"

Replace signals with new style signals and connections

Before:

self.emit(SIGNAL("valuesChanged(const QStringList &)"), self.getArguments())

After:

class Test():
  valuesChagned = QtCore.pyqtSignal(list)

  def yourmethod():
    self.valuesChagned.emit(self.getArguments)

Thanks Nathan - much cleaner. How does unicode get handled with the conversion of QString?

Chris, I think in Python 2.7 it will QString == str but in Python 3 QString == unicode. So for QGIS you need to do unicode(lineedit.text()) if you want unicode strings.

I have answered in the QGIS user list and this is very good news indeed: the end of the PyQt "pollution" in the data processing. Thank you very much Nathan

@NathanW2: isn't it opposite? In Python 2.x QString is directly mapped to unicode. In 3.0 I guess it's not necessary so it stays in the "plain" str.

I think you are right.

For example, an application can choose whether QString is implemented as a Python type, or is automatically converted to and from a Python v2 unicode object or a Python v3 string object.