issues.md

Common issues in PyQt5-Stubs

#1 Mixed overloads with static and non-static methods

Example

class QImageReader(sip.simplewrapper):

    # this is a static method
    @typing.overload
    @staticmethod
    def imageFormat(fileName: str) -> QtCore.QByteArray: ...

    # also static
    @typing.overload
    @staticmethod
    def imageFormat(device: QtCore.QIODevice) -> QtCore.QByteArray: ...

    # non-static
    @typing.overload
    def imageFormat(self) -> QImage.Format: ...

mypy error:

Overload does not consistently use the "@staticmethod" decorator on all function signatures.

Solution

None, yet. Backup solution is to use #type: ignore to eleminate the mypy error.

class QImageReader(sip.simplewrapper):

    # this is a static method
    @typing.overload  # type: ignore
    @staticmethod
    def imageFormat(fileName: str) -> QtCore.QByteArray: ...

    # also static
    @typing.overload
    @staticmethod
    def imageFormat(device: QtCore.QIODevice) -> QtCore.QByteArray: ...

    # non-static
    @typing.overload
    def imageFormat(self) -> QImage.Format: ...  # type: ignore

#2 Method signature is incompatible with supertype

Description

The Liskov substitution principle demands derivated classes to not narrow method arguments and to not widen method return types. This principle is not always respected by the Qt5 codebase.

Example

class QPaintDevice(sip.simplewrapper):
    # ...
    def devicePixelRatio(self) -> int: ...
    # ...


class QPixmap(QPaintDevice):
    # ...
    def devicePixelRatio(self) -> float: ...
    # ...

mypy error:

Return type "float" of "devicePixelRatio" incompatible with return type "int" in supertype "QPaintDevice".

Solution

Actually it should be avoided to narrow inputs or broaden outputs of derived classes. As mypy demands to respect the Liskov substitution principle there is no way to prevent this error from happening. However, due to the given codebase of PyQt5 and Qt5 itself the only way to avoid this error from occuring is to use # type: ignore.

class QPaintDevice(sip.simplewrapper):
    # ...
    def devicePixelRatio(self) -> int: ...
    # ...


class QPixmap(QPaintDevice):
    # ...
    def devicePixelRatio(self) -> float: ...  # type: ignore
    # ...

#3 Overloaded function signatures with incompatible return types

Description

Example

class QMatrix4x4(sip.simplewrapper):

    @typing.overload
    def map(self, point: QtCore.QPoint) -> QtCore.QPoint: ...
    @typing.overload
    def map(self, point: typing.Union[QtCore.QPointF, QtCore.QPoint]) -> QtCore.QPointF: ...

mypy error: Overloaded function signatures 1 and 2 overlap with incompatible return types.

Solution

Fix the function signatures that there is a unique return type for each overload. Removing the Union in the second signature be the right thing to do in the example.

class QMatrix4x4(sip.simplewrapper):

    @typing.overload
    def map(self, point: QtCore.QPoint) -> QtCore.QPoint: ...
    @typing.overload
    def map(self, point: QtCore.QPointF) -> QtCore.QPointF: ...

Occurences

• QtGui.QMatrix4x4.map

#4 Overloaded function signature will never be matched

Description

Example

class QPainter(sip.simplewrapper):
    # ...
    def drawImage(self, r: QtCore.QRect, image: QImage) -> None: ...
    @typing.overload
    def drawImage(self, p: typing.Union[QtCore.QPointF, QtCore.QPoint], image: QImage) -> None: ...
    @typing.overload
    def drawImage(self, p: QtCore.QPoint, image: QImage) -> None: ...
    # ...

mypy error: Overloaded function signature 4 will never be matched: signature 3's parameter type(s) are the same or broader.

Solution

Remove the signature. This would be best to be done while generating the PyQt5 stubs.

class QPainter(sip.simplewrapper):
    # ...
    def drawImage(self, r: QtCore.QRect, image: QImage) -> None: ...
    @typing.overload
    def drawImage(self, p: typing.Union[QtCore.QPointF, QtCore.QPoint], image: QImage) -> None: ...
    # @typing.overload
    # def drawImage(self, p: QtCore.QPoint, image: QImage) -> None: ...
    # ...

Occurences

• QtGui.QPainter.drawImage

#5 Definitions of base classes are incompatible

Description

Example

class QPaintDeviceWindow(QWindow, QPaintDevice):
    # ...

mypy error: Definition of "devicePixelRatio" in base class "QWindow" is incompatible with definition in base class "QPaintDevice".

Solution

This error is due to the Qt5 codebase and can not be fixed without breaking the current codebase. So silencing the error with # type: ignore seems to be the right way to go.

#5 Signals need to be defined as pyqtSignal instead of functions

Description

To allow the proper use of signal functions like connect() it is necessary to define signals as variables of type pyqtSignal instead of functions.

Example

class QSignalMapper(QObject):

    from PyQt5.QtWidgets import QWidget

    def __init__(self, parent: typing.Optional[QObject] = ...) -> None: ...

    # ...
    @typing.overload
    def mapped(self, a0: int) -> None: ...
    @typing.overload
    def mapped(self, a0: str) -> None: ...
    @typing.overload
    def mapped(self, a0: QWidget) -> None: ...
    @typing.overload
    def mapped(self, a0: QObject) -> None: ...
    # ...

Solution

class QSignalMapper(QObject):

    from PyQt5.QtWidgets import QWidget

    def __init__(self, parent: typing.Optional[QObject] = ...) -> None: ...

    mapped: pyqtSignal

    # ...
    # @typing.overload
    # def mapped(self, a0: int) -> None: ...
    # @typing.overload
    # def mapped(self, a0: str) -> None: ...
    # @typing.overload
    # def mapped(self, a0: QWidget) -> None: ...
    # @typing.overload
    # def mapped(self, a0: QObject) -> None: ...
    # ...

The disadvantage of this approach is that the signature of the signal is lost. But that actually does not matter as you will always need to define a slot function with the right signature anyway.

This should be fixed in the original PyQt5 stubs.

#6 Missing type annotation for typing.Any

Description

By default PyQt5 stubs do not contain type annotations for typing.Any.

Example

def Q_FLAGS(*a0) -> None: ...

mypy error: Function is missing a type annotation for one or more arguments.

Solution

Add type annotation of type typing.Any.

This should be fixed in the original PyQt5 stubs.