class QTimer

The QTimer class provides repetitive and single-shot timers. More…

Inheritance diagram of PySide6.QtCore.QTimer

Synopsis

Properties

Methods

Slots

Signals

Static functions

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

The QTimer class provides a high-level programming interface for timers. To use it, create a QTimer , connect its timeout() signal to the appropriate slots, and call start() . From then on, it will emit the timeout() signal at constant intervals.

Example for a one second (1000 millisecond) timer (from the Analog Clock example):

timer = QTimer(self)
timer.timeout.connect(this, QOverload<>::of(&AnalogClock::update))
timer.start(1000)

From then on, the update() slot is called every second.

You can set a timer to time out only once by calling setSingleShot (true). You can also use the static singleShot() function to call a slot after a specified interval:

QTimer::singleShot(200, self.updateCaption)

In multithreaded applications, you can use QTimer in any thread that has an event loop. To start an event loop from a non-GUI thread, use exec() . Qt uses the timer’s thread affinity to determine which thread will emit the timeout() signal. Because of this, you must start and stop the timer in its thread; it is not possible to start a timer from another thread.

As a special case, a QTimer with a timeout of 0 will time out as soon as possible, though the ordering between zero timers and other sources of events is unspecified. Zero timers can be used to do some work while still providing a snappy user interface:

timer = QTimer(self)
timer.timeout.connect(self.processOneThing)
timer.start()

From then on, processOneThing() will be called repeatedly. It should be written in such a way that it always returns quickly (typically after processing one data item) so that Qt can deliver events to the user interface and stop the timer as soon as it has done all its work. This is the traditional way of implementing heavy work in GUI applications, but as multithreading is nowadays becoming available on more and more platforms, we expect that zero-millisecond QTimer objects will gradually be replaced by QThread s.

Accuracy and Timer Resolution

The accuracy of timers depends on the underlying operating system and hardware. Most platforms support a resolution of 1 millisecond, though the accuracy of the timer will not equal this resolution in many real-world situations.

The accuracy also depends on the timer type . For PreciseTimer , QTimer will try to keep the accuracy at 1 millisecond. Precise timers will also never time out earlier than expected.

For CoarseTimer and VeryCoarseTimer types, QTimer may wake up earlier than expected, within the margins for those types: 5% of the interval for CoarseTimer and 500 ms for VeryCoarseTimer .

All timer types may time out later than expected if the system is busy or unable to provide the requested accuracy. In such a case of timeout overrun, Qt will emit timeout() only once, even if multiple timeouts have expired, and then will resume the original interval.

Alternatives to QTimer

Qt 6.8 introduced QChronoTimer . The main difference between the two classes, is that QChronoTimer supports a larger interval range and a higher precision (std::chrono::nanoseconds). For QTimer the maximum supported interval is ±24 days, whereas for QChronoTimer it is ±292 years (less chances of interger overflow with intervals longer than std::numeric_limits<int>::max()). If you only need millisecond resolution and ±24 days range, you can continue to use QTimer .

Another alternative is reimplementing the timerEvent() method in your class (which must be a sub-class of QObject ), and using one of the following approaches:

  • Using QBasicTimer , a lightweight value-class wrapping a timer ID. You can start the timer with QBasicTimer::start() and stop it with stop() . You can handle the event in your reimplemneted timerEvent() .

  • A more low-level method is manipulating the timer IDs directly. To start the timer call startTimer() , storing the returned ID. To stop the timer call killTimer() . You can handle the event in your reimplemented timerEvent() . This approach is typically more cumbersome than using QBasicTimer .

A disadvantage of using timerEvent() is that some high-level features, such as single-shot timers and signals, aren’t supported.

Some operating systems limit the number of timers that may be used; Qt tries to work around these limitations.

See also

QBasicTimer QTimerEvent timerEvent() Timers Analog Clock

Note

Properties can be used directly when from __feature__ import true_property is used or via accessor functions otherwise.

property activeᅟ: bool

This boolean property is true if the timer is running; otherwise false.

Access functions:
property intervalᅟ: int

This property holds the timeout interval in milliseconds.

The default value for this property is 0. A QTimer with a timeout interval of 0 will time out as soon as all the events in the window system’s event queue have been processed.

Setting the interval of a running timer will change the interval, stop() and then start() the timer, and acquire a new id() . If the timer is not running, only the interval is changed.

See also

singleShot

Access functions:
property remainingTimeᅟ: int

This property holds the remaining time in milliseconds.

Returns the timer’s remaining value in milliseconds left until the timeout. If the timer is inactive, the returned value will be -1. If the timer is overdue, the returned value will be 0.

See also

interval

Access functions:
property singleShotᅟ: bool

This property holds whether the timer is a single-shot timer.

A single-shot timer fires only once, non-single-shot timers fire every interval milliseconds.

The default value for this property is false.

Access functions:
property timerTypeᅟ: Qt.TimerType

This property holds controls the accuracy of the timer.

The default value for this property is Qt::CoarseTimer.

See also

TimerType

Access functions:
__init__([parent=None])
Parameters:

parent – QObject

Constructs a timer with the given parent.

id()
Return type:

TimerId

Returns a TimerId representing the timer ID if the timer is running; otherwise returns Qt::TimerId::Invalid.

See also

TimerId

interval()
Return type:

int

See also

setInterval()

Getter of property intervalᅟ .

isActive()
Return type:

bool

Returns true if the timer is running; otherwise returns false.

Getter of property activeᅟ .

isSingleShot()
Return type:

bool

Getter of property singleShotᅟ .

remainingTime()
Return type:

int

Getter of property remainingTimeᅟ .

setInterval(msec)
Parameters:

msec – int

See also

interval()

Setter of property intervalᅟ .

setSingleShot(singleShot)
Parameters:

singleShot – bool

See also

singleShot()

Setter of property singleShotᅟ .

setTimerType(atype)
Parameters:

atype – TimerType

See also

timerType()

Setter of property timerTypeᅟ .

static singleShot(msec, functor)
Parameters:

  • msec – int

  • functor – PyCallable

static singleShot(msec, context, functor)
Parameters:

  • msec – int

  • context – QObject

  • functor – PyCallable

static singleShot(msec, receiver, member)
Parameters:

  • msec – int

  • receiver – QObject

  • member – str

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

Use the chrono overloads. This static function calls a slot after a given time interval.

It is very convenient to use this function because you do not need to bother with a timerEvent or create a local QTimer object.

Example:

from PySide6.QtWidgets import QApplication
from PySide6.QtCore import QTimer
if __name__ == "__main__":

    app = QApplication([])
    QTimer.singleShot(600000, app, QCoreApplication.quit)
    ...
    sys.exit(app.exec())

This sample program automatically terminates after 10 minutes (600,000 milliseconds).

The receiver is the receiving object and the member is the slot. The time interval is msec milliseconds.

See also

start()

static singleShot(msec, timerType, receiver, member)
Parameters:

This is an overloaded function.

Use the chrono overloads. This static function calls a slot after a given time interval.

It is very convenient to use this function because you do not need to bother with a timerEvent or create a local QTimer object.

The receiver is the receiving object and the member is the slot. The time interval is msec milliseconds. The timerType affects the accuracy of the timer.

See also

start()

start()

This function overloads start().

Starts or restarts the timer with the timeout specified in interval .

If the timer is already running, it will be stopped and restarted. This will also change its id() .

If singleShot is true, the timer will be activated only once.

start(msec)
Parameters:

msec – int

Starts or restarts the timer with a timeout interval of msec milliseconds.

If the timer is already running, it will be stopped and restarted. This will also change its id() .

If singleShot is true, the timer will be activated only once. This is equivalent to:

timer.setInterval(msec);
timer.start();

Note

Keeping the event loop busy with a zero-timer is bound to cause trouble and highly erratic behavior of the UI.

stop()

Stops the timer.

See also

start()

timeout()

This signal is emitted when the timer times out.

timerId()
Return type:

int

Returns the ID of the timer if the timer is running; otherwise returns -1.

timerType()
Return type:

TimerType

See also

setTimerType()

Getter of property timerTypeᅟ .