PyQt4 and Python v3 — PyQt 4.10.1 Reference Guide

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# PyQt4 and Python v3

PyQt4 fully supports all versions of Python v3. The default behaviour is different in some areas to the default behaviour with Python v2. These incompatible differences were introduced in order to make PyQt4 more Pythonic. However it is very easy to revert to the default Python v2 behaviour on a class by class basis if required. (See the section Selecting Incompatible APIs.)

## QAbstractSpinBox

The following PyQt4 calls have changed signatures to avoid the need for mutable strings:

    QAbstractSpinBox.fixup(str input) -> str
    QAbstractSpinBox.validate(str input, int pos) -> QValidator.State, str, int

## QChar

The `QChar` class is implemented as a mapped type that is automatically converted to and from a Python string.

## QClipboard

The following PyQt4 call has a changed signature to avoid the need for mutable strings:

    QClipboard.text(str subtype, QClipboard.Mode mode=QClipboard.Clipboard) -> str, str

## QDate

The `QDate.__hash__()` returns a hash of the string representation so that two objects with the same date will have the same hash.

The default behaviour with Python v2 is to return the object’s `id()` so that two objects with the same date will have different hashes.

## QDateTime

The `QDateTime.__hash__()` method returns a hash of the string representation so that two objects with the same date and time will have the same hash.

The default behaviour with Python v2 is to return the object’s `id()` so that two objects with the same date and time will have different hashes.

## QDateTimeEdit

The following PyQt4 calls have changed signatures to avoid the need for mutable strings:

    QDateTimeEdit.fixup(str input) -> str
    QDateTimeEdit.validate(str input, int pos) -> QValidator.State, str, int

## QDoubleSpinBox

The following PyQt4 calls have changed signatures to avoid the need for mutable strings:

    QDoubleSpinBox.fixup(str input) -> str
    QDoubleSpinBox.validate(str input, int pos) -> QValidator.State, str, int

## QDoubleValidator

The following PyQt4 call has a changed signature to avoid the need for mutable strings:

    QDoubleValidator.validate(str input, int pos) -> QValidator.State, str, int

## QFileDialog

The following PyQt4 calls have changed signatures to avoid the need for mutable strings:

    QFileDialog.getOpenFileName(QWidget parent=None, str caption=None, str dir=None, str filter=None, QFileDialog.Options options=0) -> str
    QFileDialog.getOpenFileNames(QWidget parent=None, str caption=None, str dir=None, str filter=None, QFileDialog.Options options=0) -> list(str)
    QFileDialog.getSaveFileName(QWidget parent=None, str caption=None, str dir=None, str filter=None, QFileDialog.Options options=0) -> str

The static methods `QFileDialog.getOpenFileNameAndFilter()`, `QFileDialog.getOpenFileNamesAndFilter()` and `QFileDialog.getSaveFileNameAndFilter()` have been added which return a tuple of the name(s) and the selected filter. These can also be used with Python v2.

## QFontMetrics

The methods `QFontMetrics.widthChar()` and `QFontMetrics.boundingRectChar()` have been added which accept a Python string of length one and call the C++ `QFontMetrics::width()` and `QFontMetrics::boundingRect()` methods passing the character as a `QChar` (rather than a single character `QString`).

## QFontMetricsF

The methods `QFontMetricsF.widthChar()` and `QFontMetricsF.boundingRectChar()` have been added which accept a Python string of length one and call the C++ `QFontMetricsF::width()` and `QFontMetricsF::boundingRect()` methods passing the character as a `QChar` (rather than a single character `QString`).

## QIntValidator

The following PyQt4 call has a changed signature to avoid the need for mutable strings:

    QIntValidator.validate(str input, int pos) -> QValidator.State, str, int

## QLatin1Char

The `QLatin1Char` class is not implemented.

## QLatin1String

The `QLatin1String` class is not implemented.

## QPyNullVariant

The `QPyNullVariant` class is used to represent a null `QVariant`. It is automatically converted to a C++ `QVariant` when required.

A null C++ `QVariant` is automatically converted to a `QPyNullVariant` unless the type of the data in the `QVariant` itself supports the concept of a null value (i.e. it has an `isNull()` method). In this case a null C++ `QVariant` is converted to a null instance of the data type. The exception to this rule is that a C++ `QVariant` containing a null `QString` is always converted to a `QPyNullVariant`.

## QRegExpValidator

The following PyQt4 call has a changed signature to avoid the need for mutable strings:

    QRegExpValidator.validate(str input, int pos) -> QValidator.State, str, int

## QSettings

The `QSettings.value()` method takes an optional `type` keyword argument that specifies the type of the value to return. It can either be a Python type object or a string specifying the name of a C++ type.

Using this argument avoids potential portability problems where the type of a value may not be as expected because the platform specific backend to `QSettings` may not store the necessary type information.

The argument can also be used with Python v2.

## QSpinBox

The following PyQt4 calls have changed signatures to avoid the need for mutable strings:

    QSpinBox.fixup(str input) -> str
    QSpinBox.validate(str input, int pos) -> QValidator.State, str, int

## QString

The `QString` class is implemented as a mapped type that is automatically converted to and from a Python string. In addition a `None` is converted to a null `QString`. However, a null `QString` is converted to an empty Python string (and not `None`). (This is because Qt often returns a null `QString` when it should probably return an empty `QString`.)

## QStringList

The `QStringList` class is implemented as a mapped type that is automatically converted to and from a Python list of strings.

## QStringMatcher

The `QStringMatcher` class is not implemented.

## QStringRef

The `QStringRef` class is implemented as a mapped type that is automatically converted to and from a Python string.

## QTextDecoder

The following C++ call is not wrapped because it expects `QString` to be mutable:

    void toUnicode(QString *target, const char *chars, int len)

## QTextStream

The C++ functions `bin()`, `hex()` and `oct()` are named `bin_()`, `hex_()` and `oct_()` respectively in Python. This allows the import style `from PyQt4.QtCore import *` to be used without them clashing with the Python built-in functions with the same names.

The following C++ calls are not wrapped because they expect `QString` to be mutable:

    QTextStream(QString *string, QIODevice::OpenMode openMode = QIODevice::ReadWrite)
    void setString(QString *string, QIODevice::OpenMode openMode = QIODevice::ReadWrite)
    QString *string()
    QTextStream &operator>>(QChar &c)
    QTextStream &operator>>(QString &s)

## QTime

The `QTime.__hash__()` returns a hash of the string representation so that two objects with the same time will have the same hash.

The default behaviour with Python v2 is to return the object’s `id()` so that two objects with the same time will have different hashes.

## QUrl

The `QUrl.__hash__()` method returns a hash of the string representation so that two objects with the same URL will have the same hash.

The default behaviour with Python v2 is to return the object’s `id()` so that two objects with the same URL will have different hashes.

## QValidator

The following PyQt4 calls have changed signatures to avoid the need for mutable strings:

    QValidator.fixup(str input) -> str
    QValidator.validate(str input, int pos) -> QValidator.State, str, int

## QVariant

The `QVariant` class is implemented as a mapped type. Any Python object can be passed when a `QVariant` instance is expected. When Qt returns a `QVariant` then it will automatically be converted to the original Python object or an equivalent.

`None` is interpreted as an invalid `QVariant` and vice versa.

The `QPyNullVariant` class is used to represent a null `QVariant`.

## QWebPage

The following PyQt4 call has a changed signature to avoid the need for mutable strings:

    QWebPage.javaScriptPrompt(QWebFrame originatingFrame, str msg, str defaultValue) -> bool, str

## QXmlStreamWriter

The following C++ call is not wrapped because it expects `QString` to be mutable:

    QXmlStreamWriter(QString *string)

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