使用python限制类实例的数量 [英] Limit number of class instances with python
问题描述
ΜyMainclass创建一个简单的 QmainWindows
,如下所示:
mcManageUiC(QtGui.QMainWindow):
def __init __(self):
super(mcManageUiC,self).__ init __()
self.initUI()
def initUI(self):
self.show()
我的文件我这样启动它:
def main():
app = QtGui.QApplication argv)
renderManagerVar = mcManageUiC()
sys.exit(app.exec_())
如果__name__ =='__main__':
main ()
我的问题是每次我来源时,它会启动一个新窗口。
我想知道是否有一种方法来检测我的脚本中是否存在以前的类实例(以便我关闭旧的或避免启动一个新的)或任何其他解决方案?
此外,当使用py2exe编译我的代码时,与Windows上的.exe文件同样的问题;它每次都会启动一个新窗口。我可以在setup.py中添加一些东西,不能像这样做吗?
是可能的,如果是,那么如何?
注意:我使用Windows 7 64位编译与eclipse。
做这个,你可以使用Class属性来存储所有的实例 - 如果你这样做,你可能想通过weakref模块存储它们作为弱引用,以防止垃圾收集的问题:
class MyClass(object):
_instances = []
def __init __(self):
if(len ._instances)> 2):
self._instances.pop(0).kill()#kill最旧的实例
self._instances.append(self)
def kill(self):
pass #Do something to kill the instance
丑陋。您可能还需要考虑使用某种Factory(有条件地)创建一个新实例。这个方法更简单一些。
import weakref
class Factory(object):
def __init__ (self,cls,nallowed):
self.product_class = cls#这个工厂生产的类
self.nallowed = nallowed#允许的实例数量
self.products = []
def __call __(self,* args,** kwargs):
self.products = [x for self.products如果x()不是无] #filter输出死对象
if(len(self.products)< = self.nallowed):
newproduct = self.product_class(* args,** kwargs)
self.products.append(weakref.ref(newproduct) )
return newproduct
else:
return None
#此工厂将创建最多2个MyClass实例
#并拒绝创建更多,直到其中至少有一个
#instances已经死了。
factory = Factory(MyClass,2)
i1 = factory(foo,bar)#instance of MyClass
i2 = factory(bar,baz)#instance of MyClass
i3 = factory(baz,chicken)#None
Μy Mainclass creates a simple QmainWindows
like this:
class mcManageUiC(QtGui.QMainWindow):
def __init__(self):
super(mcManageUiC, self).__init__()
self.initUI()
def initUI(self):
self.show()
And at the end of my file I launch it like this:
def main():
app = QtGui.QApplication(sys.argv)
renderManagerVar = mcManageUiC()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
My problem is that each time i source it, it launches a new window. I would like to know if there is a way to detect existence of previous class instance in my script (so that I close the old one or avoid launching a new one), or any other solutions?
Also, when compiling my code with py2exe, same problem with my .exe file on Windows; it launchs a new window every time. Could i add something in the setup.py for Windows to not act like this?
Is it possible, if yes then how?
Note: I'm using Windows 7 64bit compiling with eclipse.
There are a couple ways to do this, you can use a Class attribute to store all the instances -- If you do it this way, you may want to store them as weak references via the weakref module to prevent issues with garbage collecting:
class MyClass(object):
_instances=[]
def __init__(self):
if(len(self._instances) > 2):
self._instances.pop(0).kill() #kill the oldest instance
self._instances.append(self)
def kill(self):
pass #Do something to kill the instance
This is a little ugly though. You might also want to consider using some sort of Factory which (conditionally) creates a new instance. This method is a little more general.
import weakref
class Factory(object):
def __init__(self,cls,nallowed):
self.product_class=cls #What class this Factory produces
self.nallowed=nallowed #Number of instances allowed
self.products=[]
def __call__(self,*args,**kwargs):
self.products=[x for x in self.products if x() is not None] #filter out dead objects
if(len(self.products) <= self.nallowed):
newproduct=self.product_class(*args,**kwargs)
self.products.append(weakref.ref(newproduct))
return newproduct
else:
return None
#This factory will create up to 2 instances of MyClass
#and refuse to create more until at least one of those
#instances have died.
factory=Factory(MyClass,2)
i1=factory("foo","bar") #instance of MyClass
i2=factory("bar","baz") #instance of MyClass
i3=factory("baz","chicken") #None
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