Python，创建对象

I’m trying to learn python and I now I am trying to get the hang of classes and how to manipulate them with instances.

I can’t seem to understand this practice problem:

Create and return a student object whose name, age, and major are the same as those given as input

def make_student(name, age, major)

I just don’t get what it means by object, do they mean I should create an array inside the function that holds these values? or create a class and let this function be inside it, and assign instances? (before this question i was asked to set up a student class with name, age, and major inside)

class Student:
    name = "Unknown name"
    age = 0
    major = "Unknown major"

class Student(object):
    name = ""
    age = 0
    major = ""

    # The class "constructor" - It's actually an initializer 
    def __init__(self, name, age, major):
        self.name = name
        self.age = age
        self.major = major

def make_student(name, age, major):
    student = Student(name, age, major)
    return student

Note that even though one of the principles in Python’s philosophy is “there should be one—and preferably only one—obvious way to do it”, there are still multiple ways to do this. You can also use the two following snippets of code to take advantage of Python’s dynamic capabilities:

class Student(object):
    name = ""
    age = 0
    major = ""

def make_student(name, age, major):
    student = Student()
    student.name = name
    student.age = age
    student.major = major
    # Note: I didn't need to create a variable in the class definition before doing this.
    student.gpa = float(4.0)
    return student

I prefer the former, but there are instances where the latter can be useful – one being when working with document databases like MongoDB.

Create a class and give it an __init__ method:

class Student:
    def __init__(self, name, age, major):
        self.name = name
        self.age = age
        self.major = major

    def is_old(self):
        return self.age > 100

Now, you can initialize an instance of the Student class:

>>> s = Student('John', 88, None)
>>> s.name
    'John'
>>> s.age
    88

Although I’m not sure why you need a make_student student function if it does the same thing as Student.__init__.

Objects are instances of classes. Classes are just the blueprints for objects. So given your class definition –

# Note the added (object) - this is the preferred way of creating new classes
class Student(object):
    name = "Unknown name"
    age = 0
    major = "Unknown major"

You can create a make_student function by explicitly assigning the attributes to a new instance of Student –

def make_student(name, age, major):
    student = Student()
    student.name = name
    student.age = age
    student.major = major
    return student

But it probably makes more sense to do this in a constructor (__init__) –

class Student(object):
    def __init__(self, name="Unknown name", age=0, major="Unknown major"):
        self.name = name
        self.age = age
        self.major = major

The constructor is called when you use Student(). It will take the arguments defined in the __init__ method. The constructor signature would now essentially be Student(name, age, major).

If you use that, then a make_student function is trivial (and superfluous) –

def make_student(name, age, major):
    return Student(name, age, major)

For fun, here is an example of how to create a make_student function without defining a class. Please do not try this at home.

def make_student(name, age, major):
    return type('Student', (object,),
                {'name': name, 'age': age, 'major': major})()

when you create an object using predefine class, at first you want to create a variable for storing that object. Then you can create object and store variable that you created.

class Student:
     def __init__(self):

# creating an object....

   student1=Student()

Actually this init method is the constructor of class.you can initialize that method using some attributes.. In that point , when you creating an object , you will have to pass some values for particular attributes..

class Student:
      def __init__(self,name,age):
            self.name=value
            self.age=value

 # creating an object.......

     student2=Student("smith",25)