class

polymorphism: calling overrided functions without pointers

由 点点圈 提交于 2020-05-14 08:49:38
问题 I am doing some experimentation with C++. I've been imporessioned by some behaviours with polymorphism. In other languages (such as c#), when I assign an object based on a derived class to an object of BaseType: this object starts working with the derived class code. Or If I have a list of BaseType objects and I put derived class based objects in it: every element works according to the specific Type. In c++ no... I obtained this behaiviour in C++ just using pointers. Is there an alternative

python async special class methods __delete__

由 ￣綄美尐妖づ 提交于 2020-05-13 14:14:02
问题 Strait to the point: How can I async def specials class methods like __delete__ in python ? Why I need this: In order to implement a nice caching system shared between multiple process, I want to retrieve the data from the database once and store them in a cache, modify the data in the cache and when the data is not used anymore: update the database. My problem is, in order to know which instance is the last one, I want to use the __delete__ special method asyncly def asyncinit(cls): ""

How to toggle/switch class of a div onclick using only javascript

由 你。 提交于 2020-05-11 02:54:40
问题 I want a div to switch its class (toggle) onclick and then revert back to original class onclick again My code is: function myfunc() { //the code over here } .normal { width:25%; height:25%; background: #f00; } .active { width:100%; height:100%; background: #f00; } #div{} <body> <div id="div" onclick="myfunc()">click here</div> </body> 回答1: using pure js: <div id="div" class="normal" onclick="myfunc(this)">click here</div> js function myfunc(div) { var className = div.getAttribute("class");

Why a final class cannot be inherited but a final method can be inherited?

由 岁酱吖の 提交于 2020-05-10 06:24:39
问题 I have a big confusion in the usage of "final" keyword between classes and methods i.e.why final methods only support inheritance but not final classes final class A{ void print(){System.out.println("hello world");} } class Final extends A{ public static void main(String[] args){ System.out.println("hello world"); } } ERROR: cannot inherit from Final A class Final extennds A{ FINAL METHOD IS.. class Bike{ final void run(){System.out.println("run");} } class Honda extends Bike{ public static

Why a final class cannot be inherited but a final method can be inherited?

由 泄露秘密 提交于 2020-05-10 06:23:27
问题 I have a big confusion in the usage of "final" keyword between classes and methods i.e.why final methods only support inheritance but not final classes final class A{ void print(){System.out.println("hello world");} } class Final extends A{ public static void main(String[] args){ System.out.println("hello world"); } } ERROR: cannot inherit from Final A class Final extennds A{ FINAL METHOD IS.. class Bike{ final void run(){System.out.println("run");} } class Honda extends Bike{ public static

Python Wrap Class Method

由 不想你离开。 提交于 2020-05-10 04:04:25
问题 I'm trying to create an object with a run method that will be wrapped by a _wrap_run method . I'd like to be able to call the method and it's wrapper by simply typing instance.run() and I'd like to be able to subclass the object so I can override the run() method and have it still execute the wrapper. More simply put, I want people to be able to subclass A and override run() but still have calls to the run() method execute the wrapper function. I'm having some difficulty with the mechanics of

Using PHP ev class (EvTimer)

由 半世苍凉 提交于 2020-05-09 10:57:31
问题 Im trying to use EvTimer class, part of PHP ev class. I have already installed ev using pecl on my linux machine and it is visible in phpinfo() . I would like to run this sample: // Create and start timer firing after 2 seconds $w1 = new EvTimer(2, 0, function () { echo "2 seconds elapsed\n"; }); Ev::run(); But even though i have ev extension installed and enabled, i receive not found error: PHP Fatal error: Class 'EvTimer' not found in /bin/test.php on line 4 Anyone know why it doesnt see

How to prevent assigning attributes to an object that have not been specified in class definition?

由 一世执手 提交于 2020-05-09 06:38:25
问题 I have defined a simple class. The suprising thing is: I can assign attributes that haven't been defined in the class definition. How is that possible? How can I prevent this from happening? See here, what I mean, this is my simple class: class Dog: def __init__(self,name): self.name=name Of course I can now instanciate an object: dog = Dog('Fido') Printing Print(dog.name) yields 'Fido' . But now I just can assign to my object dog new attributes though I haven't included them in the class

How to prevent assigning attributes to an object that have not been specified in class definition?

由 纵饮孤独 提交于 2020-05-09 06:38:13
问题 I have defined a simple class. The suprising thing is: I can assign attributes that haven't been defined in the class definition. How is that possible? How can I prevent this from happening? See here, what I mean, this is my simple class: class Dog: def __init__(self,name): self.name=name Of course I can now instanciate an object: dog = Dog('Fido') Printing Print(dog.name) yields 'Fido' . But now I just can assign to my object dog new attributes though I haven't included them in the class

How to add method to existing class in Python?

由 纵饮孤独 提交于 2020-05-09 06:36:58
问题 I have this really convenient high-level pd.DataFrame saving function that I want to add to pandas . How can I add this method to the pd.DataFrame class? def to_file(df, path, sep="\t", compression="infer", pickled="infer", verbose=False, **args): _ , ext = os.path.splitext(path) # Serialization if pickled == "infer": if ext in {".pkl", ".pgz", ".pbz2"}: pickled = True else: pickled = False # Compression if compression == "infer": if pickled: if ext == ".pkl": compression = None if ext == "
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