Question

我一直收到错误：TypeError: unbound method get_num_students() must be called with Student instance as first argument (got nothing instead)

以下是代码：

class Student(object):
    num_students = 0
    num_grad_2013 = 0

    def __init__(self, first_name, last_name, id_num, yr_of_grad, counselor):
        self = self
        self.first_name = first_name
        self.last_name = last_name
        self.id_num = int(id_num)
        self.yr_of_grad = int(yr_of_grad)
        self.counselor = counselor

    def to_string(first_name, last_name, id_num, yr_of_grad, counselor):
        print first_name
        print last_name
        print id_num
        print yr_of_grad
        print counselor


    def move():
        num_students -= 1
        if yr_of_grad == 12:
            num_grad_2013 -= 1
        else:
            None
        print "Student with ID number: %s has moved." % (id_num)

    def grad_early():
        num_students -= 1
        num_grad_2013 -= 1
        print "Student with ID number: %s is graduating early." % (id_num)

    def get_num_students():
        print "There are %s students in this school." % (num_students)

    def get_grad_2013():
        print "There are %s students graduating this year." % (num_grad_2013)

def main():
    print "Creating student Nathan Lindquist" 
    nathan = Student("Nathan", "Lindquist", 11111, 2014, "Iverson")
    print nathan 
    print "Creating student Dylan Schlact" 
    dylan = Student("Dylan", "Schlact", 22222, 2012, "Greene") 
    print dylan 
    print "Creating student Matt Gizzo" 
    matt = Student("Matt", "Gizzo", 33333, 2013, "Connor") 
    print matt 
    # so number of students is 3, one is graduating in 2013 
    Student.get_num_students() 
    Student.get_grad_2013() 
     # change some things! 
    nathan.grad_early() 
    print nathan 
    matt.move() 
    #matt.grad_early() 
    #print matt 
    # so number of students is 2, one is graduating in 2013 
    Student.get_num_students() 
    Student.get_grad_2013()
    return

这是Python输出：

>>> main()
Creating student Nathan Lindquist
<__main__.Student object at 0x03065430>
Creating student Dylan Schlact
<__main__.Student object at 0x030653B0>
Creating student Matt Gizzo
<__main__.Student object at 0x030653D0>

Traceback (most recent call last):
  File "<pyshell#8>", line 1, in <module>
    main()
  File "C:\Users\admin\Desktop\Python\student.py", line 51, in main
    Student.get_num_students()
TypeError: unbound method get_num_students() must be called with Student instance as first argument (got nothing instead)

另外，如果有人能帮我把它打印成记忆中的空间，我也会很感激。

Answer 1

您似乎希望将grad_early，get_num_students和get_grad_2013定义为类方法，但您将它们声明为实例方法。

实例方法是一种方法，它完全属于类的实例。

一个例子是

class Student(object):
    # ...

    def print_name(self):  # This is an instance method
        print "executing instance method"

    @classmethod
    def num_of_students(cls)
        print "executing class method"

不同之处在于实例方法将起作用 s =学生（） s.print_name（）

类方法将对类本身起作用学生。

Answer 2

在python 2和3版本中的差异：

如果已经在具有相同名称的类中使用了默认方法，并且您重新声明为同名，则在您想要实例化它时，它将显示为该类实例的非绑定方法调用。

如果你想要类方法，而是将它们声明为实例方法。

实例方法是在创建类的实例时使用的方法。

一个例子是

   def user_group(self):   #This is an instance method
        return "instance method returning group"

班级标签方法：

   @classmethod
   def user_group(groups):   #This is an class-label method
        return "class method returning group"

在python 2和3版本中，不同类@classmethod要写在python 3中，它自动将其作为类标签方法获取，而不需要编写@classmethod 我想这可能会对你有帮助。

Answer 3

定义实例方法时，将printf("%zu",sizeof(num));作为方法的第一个参数，当您使用它时，在实例变量前添加self。

像：

self.

必须使用instance作为第一个参数调用unbound方法 - python

3 个答案: