Python newbie about the failure of methods in classes to obtain variables

Question

code show as below:

class Cat:
    #属性
    new_name = 0
    new_age = 0
    #方法
    def get_name(self,new_name):
        return new_name
    def get_age(self,new_age):
        return new_age
    def Attributes(self):
        self.name = self.get_name(self.new_name)
        self.age = self.get_age(self.new_age)
        print(self.name)
        print(self.age)

    def show(self):
        print(self.name)
        print(self.age)
#cat = Cat()
cat = Cat()
cat.get_name("哈哈")
cat.get_age(20)
cat.Attributes()
cat.show()

Results of the:

my question:

I have passed in 2 values, one haha ​​and one 20
Why is it still printed as 0?

Answer 1

To put it simply, your get function did not assign your variables "haha" and 20 to the attributes of the class

def get_name(self):
    return new_name
def get_age(self):
    return new_age

加两个设置函数
def set_name(self,new_name):
    self.new_name = new_name
def set_age(self,new_age):
    self.new_age = new_age

The arrow you drew actually points to the two get functions above, not your Attr function.

Answer 2

Your cat.get_name("haha") returns the value of a local variable new_name and does not change the value of self.new_name, so execute self.name = self.get_name(self.new_name) After self.name is still 0.

Answer 3

Your attributes new_name and new_age belong to Cat attributes. To assign and access class attributes, you must use class objects. Access in this class is self (representing the object of this class can be understood as the this pointer in C++, through self You can call the attributes and methods of the class), and you did not assign values ​​to the attributes of the class in get_name and get_age, but just returned the data passed in by the method, so the attributes new_name and new_age of the Cat class have not been reassigned and remain the same. 0. If you want to change the new_name and new_age values ​​of the Cat class, you can change them to:

---

def get_name(self, new_name):

self.new_name = new_name
return self.new_name

def get_age(self, new_age):

self.new_age = new_age
return self.new_age

---

Or provide set method:

---

def set_new_name(self, new_name):

self.new_name = new_name

def set_new_age(self, new_age):

self.new_age = new_age

def get_name(self):

return self.new_name

def get_age(self):

return self.new_age

Answer 4

def get_name(self, new_name):
    return new_name

This just returns the parameters of the function directly and does nothing else. You can try to execute print(cat.get_name('xxx')) to see the return result of this function. The class attribute new_name is still 0. Therefore, in Attributes, it is equivalent to passing in 0, so self.name also gets 0. This is why the printed result is still 0.

But it seems that you are still in the entry-level stage, and you may have transferred from Java. . . So if you want to fundamentally solve this type of problem, I have the following suggestions.

• Don’t use get and set naked. It is recommended to use ＠property and search this keyword to learn related knowledge.

• You try to use self to access name in the Cat class, indicating that you want this to be an instance attribute. Please put all instance attributes in __init__, and do not initialize instance attributes in other methods.

It is recommended to further consolidate the Python foundation.