Polymorphism is a core concept in Python object-oriented programming, referring to "one interface, multiple implementations", allowing for unified processing of different types of objects. 1. Polymorphism is implemented through method rewriting. Subclasses can redefine parent class methods. For example, the spoke() method of Animal class has different implementations in Dog and Cat subclasses. 2. The practical uses of polymorphism include simplifying the code structure and enhancing scalability, such as calling the draw() method uniformly in the graphical drawing program, or handling the common behavior of different characters in game development. 3. Python implementation polymorphism needs to satisfy: the parent class defines a method, and the child class overrides the method, but does not require inheritance of the same parent class. As long as the object implements the same method, this is called the "duck type". 4. Things to note include the maintenance

The computer is stuck in the "Undo Changes made to the computer" interface, which is a common problem after the Windows update fails. It is usually caused by the stuck rollback process and cannot enter the system normally. 1. First of all, you should wait patiently for a long enough time, especially after restarting, it may take more than 30 minutes to complete the rollback, and observe the hard disk light to determine whether it is still running. 2. If there is no progress for a long time, you can force shut down and enter the recovery environment (WinRE) multiple times, and try to start repair or system restore. 3. After entering safe mode, you can uninstall the most recent update records through the control panel. 4. Use the command prompt to execute the bootrec command in the recovery environment to repair the boot file, or run sfc/scannow to check the system file. 5. The last method is to use the "Reset this computer" function

Iterators are objects that implement __iter__() and __next__() methods. The generator is a simplified version of iterators, which automatically implement these methods through the yield keyword. 1. The iterator returns an element every time he calls next() and throws a StopIteration exception when there are no more elements. 2. The generator uses function definition to generate data on demand, saving memory and supporting infinite sequences. 3. Use iterators when processing existing sets, use a generator when dynamically generating big data or lazy evaluation, such as loading line by line when reading large files. Note: Iterable objects such as lists are not iterators. They need to be recreated after the iterator reaches its end, and the generator can only traverse it once.

When encountering the "RPCserverisunavailable" problem, first confirm whether it is a local service exception or a network configuration problem. 1. Check and start the RPC service to ensure that its startup type is automatic. If it cannot be started, check the event log; 2. Check the network connection and firewall settings, test the firewall to turn off the firewall, check DNS resolution and network connectivity; 3. Run the sfc/scannow and DISM commands to repair the system files; 4. Check the group policy and domain controller status in the domain environment, and contact the IT department to assist in the processing. Gradually check it in sequence to locate and solve the problem.

The problem of unavailability of the printer driver can be solved through the following steps: 1. Check the connection and ensure that the printer is turned on and connected correctly; 2. Update or reinstall the driver, and download the latest version through the device manager or official website; 3. Turn off automatic driver updates to avoid conflicts; 4. Troubleshoot other factors such as system version, permissions and security software interference. Step-by-step processing in sequence usually restores normal printing function.

To format the drive using a command prompt in Windows, it can be done via the diskpart or format command. 1. When using diskpart formatting, you need to run the command prompt as an administrator, enter diskpart, listdisk, selectdiskX (X is the disk number), listpartition, selectpartitionY (Y is the partition number), formatfs=ntfsquick to complete the formatting. 2. Use the format command to directly enter formatd:/fs:ntfs (d: is the drive letter) for operation. 3. Quick formatting does not scan bad sectors by default, complete formatting

To manage Linux user groups, you need to master the operation of viewing, creating, deleting, modifying, and user attribute adjustment. To view user group information, you can use cat/etc/group or getentgroup, use groups [username] or id [username] to view the group to which the user belongs; use groupadd to create a group, and use groupdel to specify the GID; use groupdel to delete empty groups; use usermod-aG to add users to the group, and use usermod-g to modify the main group; use usermod-g to remove users from the group by editing /etc/group or using the vigr command; use groupmod-n (change name) or groupmod-g (change GID) to modify group properties, and remember to update the permissions of relevant files.

When encountering Docker problems, you should first locate the problem, which is problems such as image construction, container operation or network configuration, and then follow the steps to check. 1. Check the container log (dockerlogs or docker-composelogs) to obtain error information; 2. Check the container status (dockerps) and resource usage (dockerstats) to determine whether there is an exception due to insufficient memory or port problems; 3. Enter the inside of the container (dockerexec) to verify the path, permissions and dependencies; 4. Review whether there are configuration errors in the Dockerfile and compose files, such as environment variable spelling or volume mount path problems, and recommend that cleanbuild avoid cache dryness