The reason for the error is NameResolutionError(self.host,self,e)frome, which is an exception type in the urllib3 library. The reason for this error is that DNS resolution failed, that is, the host name or IP address attempted to be resolved cannot be found. This may be caused by the entered URL address being incorrect or the DNS server being temporarily unavailable. How to solve this error There may be several ways to solve this error: Check whether the entered URL address is correct and make sure it is accessible Make sure the DNS server is available, you can try using the "ping" command on the command line to test whether the DNS server is available Try accessing the website using the IP address instead of the hostname if behind a proxy

Before introducing the usage of self in Python, let’s first introduce the classes and instances in Python. We know that the most important concepts of object-oriented are classes and instances. Classes are abstract templates, such as abstract things like students. , can be represented by a Student class. Instances are specific "objects" created based on classes. Each object inherits the same methods from the class, but its data may be different. 1. Take the Student class as an example. In Python, the class is defined as follows: classStudent(object):pass(Object) indicates which class the class inherits from. The Object class is all

The function of instanceof is to determine whether an object is an instance of a certain class, or whether it implements a certain interface. instanceof is an operator used to check whether an object is of a specified type. Usage scenarios of instanceof operator: 1. Type checking: can be used to determine the specific type of an object, so as to perform different logic according to different types; 2. Interface judgment: can be used to determine whether an object implements an interface, so as to determine whether an object implements an interface. The definition of the interface calls the corresponding method; 3. Downward transformation, etc.

Concept 1. This operator is used to operate on objects and check whether the object is of a specific type (type or interface type). Format 2. If the object pointed to by the variable on the left side of the calculator is an object of the class or interface on the right side of the operator, the result is true. (Objectreferencevariable)instanceof(class/interfacetype) instance packagecom.verify_instanceof;publicclassTestInstanceOf{publicstaticvoidmain(String[]args){//The following four lines of code are used to prove: instanceof

In Java, instanceof is a binary operator used to check whether an object is an instance of a class or an instance of a subclass of a class. Its syntax is "object instanceof class", where object is an object Quote, class is a class name or interface name.

The reasons for not using instanceof are: 1. The programming language you are using may not support the instanceof operator; 2. You think that using other methods can better achieve the requirements. In some cases, using other methods to check the object type may be more effective. or more suitable for your needs; 3. Not familiar with how the instanceof operator is used or unsure of its behavior; 4. In some cases, using "instanceof" may not be the best choice.

instanceof is an operator in JavaScript, used to detect whether the "prototype" attribute of the constructor appears anywhere in the prototype chain of the object. The syntax is "object instanceof constructor", where object is the object to be detected and constructor is the object to be detected. Constructor to check.

The reason is: The instanceof operator is used to check whether an object is an instance of a specific class (or its derived class). If the object is not an instance of a class, then type determination cannot be made and an error is thrown. To avoid this error, when using the instanceof operator, you need to ensure that the object is an instance of a class. If you are not sure about the type of an object, you can use other methods to determine the type.