Qt for Python Considerations

API Changes

One of the goals of PySide6 is to be API compatible with PyQt, with certain exceptions.

The latest considerations and known issues will be also reported in the wiki.

__hash__() function return value

The hash value returned for the classes PySide6.QtCore.QDate, PySide6.QtCore.QDateTime, PySide6.QtCore.QTime, PySide6.QtCore.QUrl will be based on their string representations, thus objects with the same value will produce the same hash.


Methods and functions that change the contents of a QString argument were modified to receive an immutable Python Unicode (or str) and return another Python Unicode/str as the modified string.

The following methods had their return types modified this way:

Classes: QAbstractSpinBox, QDateTimeEdit, QDoubleSpinBox, QSpinBox, QValidator

  • fixup(string): string

  • validate(string, int): [QValidator.State, string, int]

Classes: QDoubleValidator, QIntValidator, QRegExpValidator

  • validate(string, int): [QValidator.State, string, int]

Class: QClipboard

  • text(string, QClipboard.Mode mode=QClipboard.Clipboard): [string, string]

Class: QFileDialog

Instead of getOpenFileNameAndFilter(), getOpenFileNamesAndFilter() and getSaveFileNameAndFilter() like PyQt does, PySide has modified the original methods to return a tuple.

  • getOpenFileName(QWidget parent=None, str caption=None, str dir=None, str filter=None, QFileDialog.Options options=0): [string, filter]

  • getOpenFileNames(QWidget parent=None, str caption=None, str dir=None, str filter=None, QFileDialog.Options options=0): [list(string), filter]

  • getSaveFileName(QWidget parent=None, str caption=None, str dir=None, str filter=None, QFileDialog.Options options=0): [string, filter]

Class: QWebPage

  • javaScriptPrompt(QWebFrame, string, string): [bool, string]

Classes: QFontMetrics and QFontMetricsF

They had two new methods added. Both take a string of one character and convert to a QChar (to call the C++ counterpart):

  • widthChar(string)

  • boundingRectChar(string)


Inside this class some renames were applied to avoid clashes with native Python functions. They are: bin_(), hex_() and oct_(). The only modification was the addition of the ‘_’ character.


As QVariant was removed, any function expecting it can receive any Python object (None is an invalid QVariant). The same rule is valid when returning something: the returned QVariant will be converted to its original Python object type.

When a method expects a QVariant::Type the programmer can use a string (the type name) or the type itself.

qApp “macro”

The C++ API of QtWidgets provides a macro called qApp that roughly expands to QtWidgets::QApplication->instance().

In PySide, we tried to create a macro-like experience. For that, the qApp variable was implemented as a normal variable that lives in the builtins. After importing PySide6, you can immediately use qApp.

As a useful shortcut for the action “create an application if it was not created”, we recommend:

qApp or QtWidgets.QApplication()

or if you want to check if there is one, simply use the truth value:

if qApp:
    # do something if an application was created

Comparing to None is also possible, but slightly over-specified.

Testing support

For testing purposes, you can also get rid of the application by calling:


As for 5.14.2, this is currently an experimental feature that is not fully tested.

Embedding status

In embedded mode, application objects that are pre-created in C++ don’t have a Python wrapper. The qApp variable is created together with a wrapped application. Therefore, qApp does not exist in that embedded mode. Please note that you always can use QtWidgets.QApplication.instance() instead.

Abandoned Alternative

We also tried an alternative implementation with a qApp() function that was more pythonic and problem free, but many people liked the qApp macro better for its brevity, so here it is.

Rich Comparison

There was a long-standing bug in the tp_richcompare implementation of PySide classes.

  • When a class did not implement it, the default implementation of object is used. This implements == and != like the is operator.

  • When a class implements only a single function like <, then the default implementation was disabled, and expressions like obj in sequence failed with NotImplemented.

This oversight was fixed in version 5.15.1 .

Qt for Python Features

In Qt for Python, we begin for the first time to support a more pythonic user interface. With a special import statement, you can switch on features which replace certain aspects of the Python interpreter. This is done by an import statement right after the PySide6 import.


With the statement:

from __feature__ import snake_case

all methods in the current module are switched from camelCase to snake_case. A single upper case letter is replaced by an underscore and the lower case letter.


With the statement:

from __feature__ import true_property

all getter and setter functions which are marked as a property in the Qt6 docs are replaced by Python property objects. Properties are also listed as such in the according QMetaObject of a class.

Example for both features

Some Qt for Python snippet might read:


With the above features selected, this reads:

self.table.horizontal_header().section_resize_mode = QHeaderView.Stretch

Additionally, properties can also be declared directly in Shiboken for non Qt-libraries, see property-declare.

More about features

Detailed info about features can be found here: feature-why


Qt for Python ships some Qt tools: