All Questions

I'm learning Python and stumbled upon the OOP part. At the time I did my first steps with the PHP OOP but the same thing happens to me, I don't understand how to use the self value inside a method.

I've been reading around the internet and it talks about self-referencing the class and so on, but honestly, I don't understand that concept.

For example:

class Persona:

    def inicializar(self,nom):
        self.nombre=nom

    def imprimir(self):
        print("Nombre",self.nombre)

persona1=Persona()
persona1.inicializar("Pedro")
persona1.imprimir()

persona2=Persona()
persona2.inicializar("Carla")
persona2.imprimir()

Would someone be so kind as to explain to me what this is for self?

I need to find the most efficient way to remove duplicates from a list in Python.

I am doing it this way:

for i in mj:
    if i not in mj2:
        mj2.append(i)

where kjis a list like [2, 4, 4, 4, 4, 4, 9, 9]and the output mj2is of the form:

   [2, 4, 9]

There is a more efficient way that doesn't include loops, since I have to parse large lists.

When declaring the primary key (PK) of a table (eg USER), there are several options:

• An existing field ( username) can be placed as a primary key (natural key), so the username will be validated so that there is no other equal. For example:

  CREATE TABLE usuarios(
    username VARCHAR(30) not null;
    password VARCHAR(30) not null;
    tipo_u   VARCHAR(10) null;
  
    PRIMARY KEY(username)
  ) ENGINE INNODB
  

• A new field ( iduser) can be added as a primary key (surrogate key), perhaps auto-incremental if desired. For example:

  CREATE TABLE usuarios(
    iduser   INT not null AUTO_INCREMENT;
    username VARCHAR(30) not null;
    password VARCHAR(30) not null;
    tipo_u   VARCHAR(10) null;
  
    PRIMARY KEY(iduser)
  ) ENGINE INNODB
  

Is one of the two more recommended? Which of the two ways allows a better performance in a database? What advantages does each method bring?

Is it more secure using the iduser? I really don't see much use for it, but I have seen that many sites use it like this.

I work with Git and frequently need to incorporate changes from other people in the branches I work on. When this happens there are those who recommend me to use git rebaseand others git merge.

Therefore, I would like to know: what is the difference between git rebaseand git merge?

I have declared an integer dynamic in Java, that is:

ArrayList<Integer> lista = new ArrayList<Integer>();

... I'm already adding numbers to this one.

lista.add(5); lista.add(7); lista.add(3);

What I want is to order that list, and make it look like this 3, 5, 7, and for that, I tried to use a method called sort, as follows.

lista.sort();

But he asks me for an argument that I don't know. I would like to order it from smallest to largest, although if I can sort it from largest to smallest, it doesn't matter, because then I can flip the list.

The error I have is:

The method sort(Comparator<? super Integer>) in the type ArrayList<Integer> is not applicable for the arguments ()

How do I go about applying that sort method to the list?