I've implemented a timer using QTimer inside a Singleton. The Singleton is implemented using the Borg pattern. If I start a QTimer with single shot inside a function of the Singleton it won't be executed. The same call in a function outside the Singleton works well.
This is the code:
#!/usr/bin/env python
import sys
from PyQt5.QtCore import QTimer
from PyQt5.QtWidgets import QApplication
class Borg():
_shared_state = {}
def __init__(self):
self.__dict__ = self._shared_state
class Timers(Borg):
def __init__(self):
Borg.__init__(self)
def update_not_working(self):
QTimer().singleShot(2000, Timers().update_not_working)
print('update not working')
def update_working():
QTimer().singleShot(2000, update_working)
print('update working')
if __name__ == '__main__':
app = QApplication(sys.argv)
print('start timer')
Timers().update_not_working()
update_working()
sys.exit(app.exec_())
The output is (no error, no exception):
start timer
update not working
update working
update working
....
Why is one call working and the other not? Is there something wrong with my implementation of the Borg or with the usage of QTimer?
print self in update_not_working and print Timers() in update working show that the Timers object before the event loop started is different from the one within:
update not working
<__main__.Timers instance at 0xb52162cc>
update working
<__main__.Timers instance at 0xb52162cc>
update working
<__main__.Timers instance at 0xb521650c>
update working
<__main__.Timers instance at 0xb521650c>
update working
<__main__.Timers instance at 0xb521650c>
update working
<__main__.Timers instance at 0xb521650c>
#classmethod should help here because it allows to call the method on an instance OR on the class as you do in the single shot statement.
Compare: When should I use #classmethod and when def method(self)?
This is actually just a matter of normal garbage-collection.
If you add some debugging code to your example like this:
class Timers(Borg):
def __init__(self):
Borg.__init__(self)
print('init:', self)
def update_not_working(self):
QTimer().singleShot(1, Timers().update_not_working)
print('update not working')
def __del__(self):
print('deleted:', self)
it will produce output like this:
start timer
init: <__main__.Timers object at 0x7f194bf53eb8>
init: <__main__.Timers object at 0x7f1940cfdb00>
deleted: <__main__.Timers object at 0x7f1940cfdb00>
update not working
deleted: <__main__.Timers object at 0x7f194bf53eb8>
update working
update working
As you can see, both of the Timers instances get deleted long before the single-shot timer sends its timeout() signal. And when they deleted, their instance-methods get deleted as well, which will automatically disconnect them from the signal. This shows that the Borg pattern does not produce a true singleton: it just mimics some of the behaviour of one.
If you use a real singleton class, like this:
class Timers2(object):
_instance = None
def __new__(cls):
if Timers2._instance is None:
Timers2._instance = object.__new__(cls)
return Timers2._instance
def update_not_working(self):
QTimer().singleShot(2000, Timers2().update_not_working)
print('update not working')
your example will work as expected. This is because there is only ever one instance, and it is kept alive by being cached as a class attribute.
Finally, the reason why the update_working() succeeds, is because it is a globally defined function. As with the class attribute, this ensures that it won't get garbage-collected until the script completes.
class Borg():
_shared_state = {}
def __init__(self):
self.__dict__ = self._shared_state
class Timers(Borg):
def __init__(self):
Borg.__init__(self)
#classmethod
def update_not_working(cls):
QTimer().singleShot(2000, Timers().update_not_working)
print('update not working')
def update_working():
QTimer().singleShot(2000, update_working)
print('update working')
if __name__ == '__main__':
app = QApplication(sys.argv)
print('start timer')
Timers().update_not_working()
update_working()
sys.exit(app.exec_())
Related
I'm aware of this structure
class MyThread(QThread):
def __init__(self):
super().__init__()
def run():
# do stuff
t = MyThread()
t.start()
With regular threading.Thread you can do something like this:
def stuff():
# do stuff
t = threading.Thread(target=stuff)
t.start()
Any way to do this in pyqt5 with QThreads? Something like this:
t = Qthread(target=stuff)
t.start()
I tried that but I got this error:
TypeError: 'target' is an unknown keyword argument
You can add the function to a custom argument in the __init__, create an instance attribute for its reference and then run it in the run.
class MyThread(QThread):
def __init__(self, target=None):
super().__init__()
self.target = target
def run():
if self.target:
self.target()
def stuff():
# do something
t = MyThread(target=stuff)
t.start()
Be aware that access to UI elements is not allowed in external threads, so don't use the threaded function to do anything related to UI: reading values and properties is unreliable, and writing can cause your program to crash.
I'm using init_subclass in a project, and I sort of balked when I ran into the built in method kicking off when the code first runs in the interpreter -- without being directly referenced via instantiation of the containing class or the sub-classes it enumerates.
Can someone tell me what's going on, and point me to any examples of its safe use?
class Timer():
def __init__(self):
pass
def __init_subclass__(cls):
print('Runner.', cls)
print('Timer Dictionary :', Timer.__dict__.keys())
# print(Timer.__init_subclass__()) # Forbidden fruit...
pass
class Event(Timer):
print("I'll take my own bathroom selfies...thanks anyway.")
def __init__(self):
print('This is nice, meeting on a real date.')
if __name__ == '__main__': # a good place for a breakpoint
date = Event()
date
Edit --------------------------------------------------
Based on the explanations received, original code was retooled into something useful.
class Timer():
subclasses = {}
def __init__(self):
pass
def __init_subclass__(cls, **kwargs):
print('Runner.', cls)
print('Timer Dictionary :', Timer.__dict__.keys())
# print(Timer.__init_subclass__()) # Forbidden fruit...
super().__init_subclass__(**kwargs)
cls.subclasses[cls] = []
class Event(Timer):
print("I'll take my own bathroom selfies...thanks anyway.")
def __init__(self):
print('This is nice, meeting on a real date.')
if self.__class__ in super().subclasses:
# get the index and link the two
super().subclasses[self.__class__].append(self)
if __name__ == '__main__': # a good place for a breakpoint
date = Event()
date
duty = Event()
duty
print(Timer.subclasses)
Here's a minimal example:
class Super():
def __init_subclass__(cls):
print(cls)
class Sub(Super):
pass
Running this:
$ python test.py
<class '__main__.Sub'>
Why is that? According to Python's data model docs:
Whenever a class inherits from another class, init_subclass is called on that class.
Sub inherits from Super, so Super.__init_subclass__() gets called.
Specifically, type_new() invokes init_subclass in the cpython implementation.
The rationale is detailed in PEP 487.
I'm working on a GUI application, developed in Python and its UI library : PySide2 (Qt wrapper for Python)
I have a heavy computation function I want to put on another thread in order to not freeze my UI. The Ui should show "Loading" and when the function is over, receive from it it's results and update the UI with it.
I've tried a lot of different codes, a lot of examples are working for others but not me, is it PySide2 fault ? (For example this is almost what I want to do : Updating GUI elements in MultiThreaded PyQT)
My code is :
class OtherThread(QThread):
def __init__(self):
QThread.__init__(self)
def run(self):
print 'Running......'
self.emit(SIGNAL("over(object)"), [(1,2,3), (2,3,4)])
#Slot(object)
def printHey( obj):
print 'Hey, I\'ve got an object ',
print obj
thr = OtherThread()
self.connect(thr,SIGNAL("over(object)"),printHey)
thr.start()
My code is working if I use primitives such as bool or int but not with object. I see 'Running....' but never the rest.
Hope someone can enlighten me
You can't define signals dynamically on a class instance. They have to be defined as class attributes. You should be using the new-style signals and slot syntax.
class OtherThread(QThread):
over = QtCore.Signal(object)
def run(self):
...
self.over.emit([(1,2,3), (2,3,4)])
class MyApp(QtCore.QObject)
def __init__(self):
super(MyApp, self).__init__()
self.thread = OtherThread(self)
self.thread.over.connect(self.on_over)
self.thread.start()
#QtCore.Slot(object)
def on_over(self, value):
print 'Thread Value', value
Am struggling to comprehend how to split code in (Py)Qt. The aim is to have the design & navigation tabs in QMainWindow, each tab triggering code in other files. So far it only launches with the ActionClass in the same document / putting in an external document causes 'app not defined' when clicking the tab. The below works without errors, but is clunky.
class Main(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
self.u = Ui_MainWindow()
self.u.setupUi(self)
self.u.tabs.currentChanged.connect(self.TabsChanged)
def TabsChanged(self, i):
if i == self.u.tabs.indexOf(self.u.tabFirst): ActionClass.__init__
class ActionClass(Main):
def __init__(self):
app.u.lineEdit.setText("test")
app = Main()
app.show()
sys.exit(app.exec_())
The examples I keep seeing have all code in one document. Is there another way to do this e.g. where the ActionClass is in another file/writing u.lineEdit.setText instead of app.u.lineEdit.setText. It seems inheritance & an instance of Main can't be accessed from the ActionClasses doc, so I can't see how they would communicate back to the Main?
Much appreciated
As suggest #M4rtini you can separate your code into python modules. And then import them (use them) in your main module.
For instance the code you posted can be separated in to files:
# actions_class.py
class ActionClass(Main):
def __init__(self):
app.u.lineEdit.setText("test")
and
# main.py
from action_class import ActionClass # This line no need much explanation ;)
class Main(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
self.u = Ui_MainWindow()
self.u.setupUi(self)
self.u.tabs.currentChanged.connect(self.TabsChanged)
def TabsChanged(self, i):
if i == self.u.tabs.indexOf(self.u.tabFirst): ActionClass.__init__
app = Main()
app.show()
sys.exit(app.exec_())
In order to understand how import works see the link I left you above.
More explanation
Lest's see:
The correct way of executin code inside a __init__ method is creating an instance. See the example below.
class A:
def __init__(self):
print("Executing A.__init__")
print("Doing things wrong")
A.__init__ # This don't print enything
print("Doing things well")
A() # This works as expected.
So, you line reads:
if i == self.u.tabs.indexOf(self.u.tabFirst): ActionClass.__init__
and should reads:
if i == self.u.tabs.indexOf(self.u.tabFirst): ActionClass()
On the other hand, is a bad practice put code that's not for initialize the instance inside the __init__ methods.
If you don't need the instance but yet you want to store the functions inside a class (something like a c++ namespace) you creating
use #staticmethod decorator.
class A:
#staticmethod
def foo():
print("Oh, wow, a static method in Python!")
A.foo()
So, your ActionClass could be rewritten as:
class ActionClass(Main):
#staticmethod
def do_action:
app.u.lineEdit.setText("test")
ans then you can use it like this:
if i == self.u.tabs.indexOf(self.u.tabFirst): ActionClass.do_action()
I have the following code:
class Functions(QObject):
mysig = Signal(filename)
def __init__(self, parent=None):
super(Functions, self).__init__(parent)
self.result = None
def showDialog(self, filename):
self.mysig.emit(filename)
def grabResult(self):
while not self.result:
time.sleep(5)
return result #this is the question
def setResult(self, result):
self.result = result
The other part of the code has this:
class Dialog(QDialog):
anotherSig = Signal(str)
fun = Functions()
def __init__(self, parent=None, filename=filename):
self.filename = filename
#Here it displays a picture based on the filename parameter
def okButtonClicked(self):
text = self.lineedit.text()
fun.setResult(text)
#Tried also this:
self.anotherSig.emit(text)
The Functions() class is called from a worker QThread (not shown here).
I guess my question is this: how do I tell my Functions class that the user has entered the the text and clicked the OK button? I tried connecting that anotherSig Signal, but when I try to do so, Qt complains about QPixmaps not being safe to be set from a different thread, and it doesn't work.
The method that I am using here "works", but I feel it's not very reliable. Plus, it only works when all of the relevant methods in the Functions class are #classmethod - this way, for some reason, it doesn't work. The setResult is called (I added a print statement to make sure), but the grabResult still shows self.result as None.
This code is not working because the call to showDialog is happening on the instantiation of a Functions object that is an attribute of what ever object is off on the other thread. Your fun in Dialog, which you set the result on, is a different instantiation.
To move the results back to the original Functions object I think you need to connect anotherSig of the Dialog object to the setResult function on the Functions object you want to get the results back.
Does something like this work (hard to test this with out a good bit of boiler plate).
class Functions(QObject):
mysig = Signal(filename,Functions)
def __init__(self, parent=None):
super(Functions, self).__init__(parent)
self.result = None
def showDialog(self, filename):
self.mysig.emit(filename,self)
def grabResult(self):
while not self.result:
time.sleep(5)
return result #this is the question
#QtCore.Slot(str)
def setResult(self, result):
self.result = result
def connection_fun(filename,fun):
d = Dialog(filename)
# what ever else you do in here
d.anotherSig.connect(fun.setResult))
Using time.sleep causes your application to freeze. One method for making your class wait is using QEventLoop like this:
loop = QEventLoop()
myDialog.mySignal.connect(loop.quit)
loop.exec_()