class QCoreApplication#

The QCoreApplication class provides an event loop for Qt applications without UI. More…

Inherited by: QGuiApplication, QApplication

Synopsis#

Properties#

applicationNameᅟ - The name of this application
applicationVersionᅟ - The version of this application
organizationDomainᅟ - The Internet domain of the organization that wrote this application
organizationNameᅟ - The name of the organization that wrote this application
quitLockEnabledᅟ - Whether the use of the QEventLoopLocker feature can cause the application to quit

Virtual methods#

def notify()

Signals#

def aboutToQuit()
def applicationNameChanged()
def applicationVersionChanged()
def organizationDomainChanged()
def organizationNameChanged()

Static functions#

def addLibraryPath()
def applicationDirPath()
def applicationFilePath()
def applicationName()
def applicationPid()
def applicationVersion()
def arguments()
def closingDown()
def eventDispatcher()
def exec()
def exit()
def installTranslator()
def instance()
def isQuitLockEnabled()
def isSetuidAllowed()
def libraryPaths()
def organizationDomain()
def organizationName()
def postEvent()
def processEvents()
def quit()
def removeLibraryPath()
def removePostedEvents()
def removeTranslator()
def sendEvent()
def sendPostedEvents()
def setApplicationName()
def setApplicationVersion()
def setAttribute()
def setEventDispatcher()
def setLibraryPaths()
def setOrganizationDomain()
def setOrganizationName()
def setQuitLockEnabled()
def setSetuidAllowed()
def startingUp()
def testAttribute()
def translate()

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#

This class is used by non-GUI applications to provide their event loop. For non-GUI application that uses Qt, there should be exactly one QCoreApplication object. For GUI applications, see QGuiApplication. For applications that use the Qt Widgets module, see QApplication.

QCoreApplication contains the main event loop, where all events from the operating system (e.g., timer and network events) and other sources are processed and dispatched. It also handles the application’s initialization and finalization, as well as system-wide and application-wide settings.

The Event Loop and Event Handling#

The event loop is started with a call to exec() . Long-running operations can call processEvents() to keep the application responsive.

In general, we recommend that you create a QCoreApplication , QGuiApplication or a QApplication object in your main() function as early as possible. exec() will not return until the event loop exits; e.g., when quit() is called.

Several static convenience functions are also provided. The QCoreApplication object is available from instance() . Events can be sent with sendEvent() or posted to an event queue with postEvent() . Pending events can be removed with removePostedEvents() or dispatched with sendPostedEvents() .

The class provides a quit() slot and an aboutToQuit() signal.

Application and Library Paths#

An application has an applicationDirPath() and an applicationFilePath() . Library paths (see QLibrary ) can be retrieved with libraryPaths() and manipulated by setLibraryPaths() , addLibraryPath() , and removeLibraryPath() .

Internationalization and Translations#

Translation files can be added or removed using installTranslator() and removeTranslator() . Application strings can be translated using translate() . The tr() function is implemented in terms of translate() .

Accessing Command Line Arguments#

The command line arguments which are passed to QCoreApplication ‘s constructor should be accessed using the arguments() function.

Note

QCoreApplication removes option -qmljsdebugger="...". It parses the argument of qmljsdebugger, and then removes this option plus its argument.

For more advanced command line option handling, create a QCommandLineParser .

Locale Settings#

On Unix/Linux Qt is configured to use the system locale settings by default. This can cause a conflict when using POSIX functions, for instance, when converting between data types such as floats and strings, since the notation may differ between locales. To get around this problem, call the POSIX function setlocale(LC_NUMERIC,"C") right after initializing QApplication, QGuiApplication or QCoreApplication to reset the locale that is used for number formatting to “C”-locale.

See also

QAbstractEventDispatcher QEventLoop Producer and Consumer using Semaphores Producer and Consumer using Wait Conditions

class ApplicationFlags#: New in version 4.8.

Note

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

property applicationNameᅟ: str#

This property holds the name of this application.

The application name is used in various Qt classes and modules, most prominently in QSettings when it is constructed using the default constructor. Other uses are in formatted logging output (see qSetMessagePattern() ), in output by QCommandLineParser , in QTemporaryDir and QTemporaryFile default paths, and in some file locations of QStandardPaths . Qt D-Bus, Accessibility, and the XCB platform integration make use of the application name, too.

If not set, the application name defaults to the executable name.

See also

organizationName organizationDomain applicationVersion applicationFilePath()

Access functions:

applicationName()
setApplicationName()
Signal applicationNameChanged()

property applicationVersionᅟ: str#

This property holds the version of this application.

If not set, the application version defaults to a platform-specific value determined from the main application executable or package (since Qt 5.9):

Platform

Source

Windows (classic desktop)

PRODUCTVERSION parameter of the VERSIONINFO resource

macOS, iOS, tvOS, watchOS

CFBundleVersion property of the information property list

Android

android:versionName property of the AndroidManifest.xml manifest element

Platform	Source
Windows (classic desktop)	PRODUCTVERSION parameter of the VERSIONINFO resource
macOS, iOS, tvOS, watchOS	CFBundleVersion property of the information property list
Android	android:versionName property of the AndroidManifest.xml manifest element

On other platforms, the default is the empty string.

See also

applicationName organizationName organizationDomain

Access functions:

applicationVersion()
setApplicationVersion()
Signal applicationVersionChanged()

property organizationDomainᅟ: str#

This property holds the Internet domain of the organization that wrote this application.

The value is used by the QSettings class when it is constructed using the default constructor. This saves having to repeat this information each time a QSettings object is created.

On Mac, QSettings uses organizationDomain() as the organization if it’s not an empty string; otherwise it uses organizationName() . On all other platforms, QSettings uses organizationName() as the organization.

See also

organizationName applicationName applicationVersion

Access functions:

organizationDomain()
setOrganizationDomain()
Signal organizationDomainChanged()

property organizationNameᅟ: str#

This property holds the name of the organization that wrote this application.

The value is used by the QSettings class when it is constructed using the default constructor. This saves having to repeat this information each time a QSettings object is created.

On Mac, QSettings uses organizationDomain() as the organization if it’s not an empty string; otherwise it uses organizationName(). On all other platforms, QSettings uses organizationName() as the organization.

See also

organizationDomain applicationName

Access functions:

organizationName()
setOrganizationName()
Signal organizationNameChanged()

property quitLockEnabledᅟ: bool#

This property holds Whether the use of the QEventLoopLocker feature can cause the application to quit..

The default is true.

See also

QEventLoopLocker

Access functions:

isQuitLockEnabled()
setQuitLockEnabled()

__init__(args)#

Parameters:: args – list of strings

Constructs a Qt kernel application. Kernel applications are applications without a graphical user interface. These type of applications are used at the console or as server processes.

The args argument is processed by the application, and made available in a more convenient form by the arguments() method.

__init__()

aboutToQuit()#

This signal is emitted when the application is about to quit the main event loop, e.g. when the event loop level drops to zero. This may happen either after a call to quit() from inside the application or when the user shuts down the entire desktop session.

The signal is particularly useful if your application has to do some last-second cleanup. Note that no user interaction is possible in this state.

Note

At this point the main event loop is still running, but will not process further events on return except DeferredDelete events for objects deleted via deleteLater() . If event processing is needed, use a nested event loop or call processEvents() manually.

See also

quit()

static addLibraryPath(arg__1)#

Parameters:: arg__1 – str

Prepends path to the beginning of the library path list, ensuring that it is searched for libraries first. If path is empty or already in the path list, the path list is not changed.

The default path list consists of one or two entries. The first is the installation directory for plugins, which is INSTALL/plugins, where INSTALL is the directory where Qt was installed. The second is the application’s own directory (not the current directory), but only after the QCoreApplication object is instantiated.

The library paths are reset to the default when an instance of QCoreApplication is destructed.

See also

removeLibraryPath() libraryPaths() setLibraryPaths()

static applicationDirPath()#

Return type:: str

Returns the directory that contains the application executable.

For example, if you have installed Qt in the C:\Qt directory, and you run the regexp example, this function will return “C:/Qt/examples/tools/regexp”.

On macOS and iOS this will point to the directory actually containing the executable, which may be inside an application bundle (if the application is bundled).

Warning

On Linux, this function will try to get the path from the /proc file system. If that fails, it assumes that argv[0] contains the absolute file name of the executable. The function also assumes that the current directory has not been changed by the application.

See also

applicationFilePath()

static applicationFilePath()#

Return type:: str

Returns the file path of the application executable.

For example, if you have installed Qt in the /usr/local/qt directory, and you run the regexp example, this function will return “/usr/local/qt/examples/tools/regexp/regexp”.

Warning

See also

applicationDirPath()

static applicationName()#

Return type:: str

See also

setApplicationName()

Getter of property applicationNameᅟ .

applicationNameChanged()#

Notification signal of property applicationNameᅟ .

static applicationPid()#

Return type:: int

Returns the current process ID for the application.

static applicationVersion()#

Return type:: str

See also

setApplicationVersion()

Getter of property applicationVersionᅟ .

applicationVersionChanged()#

Notification signal of property applicationVersionᅟ .

static arguments()#

Return type:: list of strings

Returns the list of command-line arguments.

Usually arguments().at(0) is the program name, arguments().at(1) is the first argument, and arguments().last() is the last argument. See the note below about Windows.

Calling this function is slow - you should store the result in a variable when parsing the command line.

Warning

On Unix, this list is built from the argc and argv parameters passed to the constructor in the main() function. The string-data in argv is interpreted using fromLocal8Bit() ; hence it is not possible to pass, for example, Japanese command line arguments on a system that runs in a Latin1 locale. Most modern Unix systems do not have this limitation, as they are Unicode-based.

On Windows, the list is built from the argc and argv parameters only if modified argv/argc parameters are passed to the constructor. In that case, encoding problems might occur.

Otherwise, the arguments() are constructed from the return value of GetCommandLine() . As a result of this, the string given by arguments().at(0) might not be the program name on Windows, depending on how the application was started.

See also

applicationFilePath() QCommandLineParser

checkPermission(permission)#

Parameters:: permission – QPermission
Return type:: PermissionStatus

Checks the status of the given permission