开发Python计算器时出现NameError: name 'add' is not defined错误求助

你的错误根源在于：add、subtract等方法是Calculator类的实例方法，不能直接作为全局函数调用。必须先创建Calculator类的实例，通过实例来调用这些方法；或者调整代码结构，把这些方法改为全局函数。

方案一：优化Calculator类并正确调用实例方法 #

首先简化Calculator类的设计（你的__init__参数冗余，不需要把choice、num1等都作为实例属性），然后在solve函数中创建类的实例，通过实例调用计算方法：

# -*- coding: utf-8 -*-
"""
Created on Mon Feb  6 23:32:23 2023

@author: John
"""

class Calculator:
    # 简化__init__，不需要多余参数
    def __init__(self):
        pass
        
    def add(self, x, y):
        return x + y
    
    def subtract(self, x, y):
        return x - y
    
    def multiply(self, x, y):
        return x * y
    
    def divide(self, x, y):
        # 新增除零判断，避免运行时错误
        if y == 0:
            return "Error: Cannot divide by zero"
        return x / y

print("Select operation.")
print("1.Add")
print("2.Subtract")
print("3.Multiply")
print("4.Divide")
    
def solve():
    # 创建Calculator实例
    calc = Calculator()
    
    while True:
        choice = input("Enter choice(1/2/3/4): ")

        if choice in ('1', '2', '3', '4'):
            try:
                num1 = float(input("Enter first number: "))
                num2 = float(input("Enter second number: "))
            except ValueError:
                print("Invalid input. Please enter a number.")
                continue

            if choice == '1':
                print(num1, "+", num2, "=", calc.add(num1, num2))

            elif choice == '2':
                print(num1, "-", num2, "=", calc.subtract(num1, num2))

            elif choice == '3':
                print(num1, "*", num2, "=", calc.multiply(num1, num2))

            elif choice == '4':
                print(num1, "/", num2, "=", calc.divide(num1, num2))
        
            next_calculation = input("Let's do next calculation? (yes/no): ")
            if next_calculation == "no":
               break
        else:
            print("Invalid Input")
solve()

方案二：直接使用全局函数（无需类） #

如果不需要面向对象的设计，可以把计算方法直接定义为全局函数，这样solve中就能直接调用：

# -*- coding: utf-8 -*-
"""
Created on Mon Feb  6 23:32:23 2023

@author: John
"""

def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    if y == 0:
        return "Error: Cannot divide by zero"
    return x / y

print("Select operation.")
print("1.Add")
print("2.Subtract")
print("3.Multiply")
print("4.Divide")
    
def solve():
    while True:
        choice = input("Enter choice(1/2/3/4): ")

        if choice in ('1', '2', '3', '4'):
            try:
                num1 = float(input("Enter first number: "))
                num2 = float(input("Enter second number: "))
            except ValueError:
                print("Invalid input. Please enter a number.")
                continue

            if choice == '1':
                print(num1, "+", num2, "=", add(num1, num2))

            elif choice == '2':
                print(num1, "-", num2, "=", subtract(num1, num2))

            elif choice == '3':
                print(num1, "*", num2, "=", multiply(num1, num2))

            elif choice == '4':
                print(num1, "/", num2, "=", divide(num1, num2))
        
            next_calculation = input("Let's do next calculation? (yes/no): ")
            if next_calculation == "no":
               break
        else:
            print("Invalid Input")
solve()

关键说明 #

• 实例方法必须通过类的实例（比如calc.add()）调用，因为这类方法依赖于类的实例对象（即使你的方法里没用到self，Python也会自动传递实例作为第一个参数）。
• 方案二更适合简单的计算器场景，方案一适合后续需要扩展更多功能（比如记录计算历史）的面向对象设计。

内容的提问来源于stack exchange，提问作者Moth