使用 self 参数调用 python 方法

Question

He guys, I'm new with Python and now I'm studying Object oriented with py. So, in my case I have a class Founds with one atributte (it will increase later), and I'm modeling to right standards. But when I call this method from another class (Main), it throws:

TypeError: val() missing 1 required positional argument: 'fundos' 

My main class where I call, instantiate this method. I prefer to use objects, because system will grow up in a few days in complexity. My main:

class Main(FlaskForm):   

    series = None 
    fundos = fundos()

    @app.route('/resultado', methods=['GET','POST'])
    def resultado():
        titulo = "Retorno da pesquisa"
       
        valuation = request.form.getlist("fundo_select")
        nomefundo = request.form.get("fii")
        fundoss = any
        fundoss = nomefundo.split(',')  
            
        **series = fundos.val(fundoss)**            

My founds class:

class Fundos(object):  
    # Atribuindo na classe como Nada
    lista_fiis=None;

    # Array de atributos da classe, inicializando
    def __init__(self):
        # Inicializando como array
        self.lista_fiis=[]


    # Pega fundos selecionados
    # Gera o relatório no excel
    def val(self, fundos):
        info_fii={}

Answer 1

In Python, unlike in Java or C++, where this. or this-> can be implied, you cannot drop self. when accessing member properties. Therefore, when you use fundos.val(fundoss) , you are not using the fundos = fundos() variable defined on the class, but instead using the class itself.

Another thing you should know about OOP and methods in Python is that you can access any method defined on the class as though it was a static method; you just have to provide it the instance yourself. In other words, given the following class:

class MyClass:
    hello(self):
        print('Hello!')

myInstance = MyClass()

calling myInstance.hello() is the same as calling MyClass.hello(myInstance) .

So, what you are doing in your call is in effect calling the method directly from the class, providing it fundoss as the self parameter and not providing the second parameter.

What you need to do is use self.fundos.val(fundoss) to use the instance you created for Main rather than the class fundos .

PS: Generally, it is a good idea to stay away from name shadowing and not use the same name for your class and instance, then these problems will be a lot easier to spot