必须以实例作为第一个参数调用未绑定的方法 - python

Question

我不断收到错误消息：TypeError: unbound method get_num_students() must be called with Student instance as first argument (got nothing instead)

代码如下：

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，如果有人可以帮助我将学生打印为内存空间，我也将不胜感激。

Answer 1

您似乎想将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。

实例方法是属于类实例的方法。

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()

并且类方法将作用于类本身 学生。

Answer 2

python 2 和 3 版本的区别：

如果您在同名的类中已经有一个默认方法，并且您重新声明为同名，那么当您想要实例化它时，它将显示为该类实例的未绑定方法调用。

如果您想要类方法，但您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"

类标签方法：

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

在 python 2 和 3 版本不同的类@classmethod 来写 在 python 3 中，它会自动将其作为类标签方法获取，并且不需要编写 @classmethod 我想这可能会对你有所帮助。

Answer 3

定义实例方法时，将self作为方法的第一个参数，使用时，在实例变量前添加self.。

喜欢：

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