python - eval 必须是字符串还是代码对象？

Question

当我运行下面的代码时，我收到以下错误： eval() arg 1 must be a string or code object

有谁知道为什么？这是我从一本书中学习的代码，所以我认为它是正确的。

 # Prompt the user to enter three numbers
number1 = eval(input("Enter the first number: "))
number2 = eval(input("Enter the second number: "))
number3 = eval(input("Enter the third number: "))

 # Compute average
average = (number1 + number2 + number3) / 3

print("The average of", number1, number2, number3, "is", average)

Answer 1

您正在使用input()Python 2，它已经eval()在输入上运行。只需删除eval()呼叫，或替换input()为raw_input().

或者，使用 Python 3 运行此代码，它显然是针对该版本的。如果您的书使用这种语法，那么您希望使用正确的版本来运行代码示例。

最重要的是，不要input()在 Python 2 或eval()Python 3 上使用。如果需要整数，请int()改用。

Python 2 示例：

# Prompt the user to enter three numbers
number1 = int(raw_input("Enter the first number: "))
number2 = int(raw_input("Enter the second number: "))
number3 = int(raw_input("Enter the third number: "))

# Compute average
average = (number1 + number2 + number3) / 3

print "The average of", number1, number2, number3, "is", average

Python 3 版本：

# Prompt the user to enter three numbers
number1 = int(input("Enter the first number: "))
number2 = int(input("Enter the second number: "))
number3 = int(input("Enter the third number: "))

# Compute average
average = (number1 + number2 + number3) / 3

print("The average of", number1, number2, number3, "is", average)