Python Slots Conflicts With Class Variable
This is a tutorial in Python3, but this chapter of our course is available in a version for Python 2.x as well: Slots, Avoiding Dynamically Created Attributes in Python 2.x Classroom Training Courses Due to the corona pandemic, we are currently running all courses online. These signals can be connected to python functions (like the dialog function in this example) so that the function is executed when a signal is triggered. These functions are called slots in Qt lingo. Subsequently, the basic syntax to trigger a slot function in response to the signal from an event is as follows widget.signal.connect(slot). In this particular example, the slot class is about 35% faster. Conclusion & Further Reading. Data classes are one of the new features of Python 3.7. With data classes, you do not have to write boilerplate code to get proper initialization, representation, and comparisons for your objects. You have seen how to define your own data classes, as. Traditional syntax: SIGNAL and SLOT QtCore.SIGNAL and QtCore.SLOT macros allow Python to interface with Qt signal and slot delivery mechanisms. This is the old way of using signals and slots. The example below uses the well known clicked signal from a QPushButton.The connect method has a non python-friendly syntax.
Pure python equivalent of the __slots__ implementation using descriptors and a metaclass.
In CPython, when class A defines __slots__=('x','y') then A.x is a 'member_descriptor' with __get__ and __set__ methods which directly access memory allocated to each instance.
As an illustration, the above code shows a rough equivalent using pure Python. In the example, when the metaclass sees that _slots_ have been defined for 'x' and 'y', it creates two additional class variables, x=Member(0) and y=Member(1). Then, it wraps the __init__() method so that new instances get created with an initialized _slotvalues list.
To make it obvious that the illustrative code is running, _slots_ is spelled with single underscores (to differentiate it from the CPython version which is spelled with double underscores).
The CPython version differs in that:
Instead of a _slotvalues pointer to an external list, CPython allocatesmemory directly inside each instance. Accordingly, the member descriptoraccesses that memory directly instead of using a list lookup.
Whenever __slots__ are present, the __new__ method prevents an instancedictionary from being created. That makes __slots__ useful for creatingvery lightweight instances.