python - 返回返回无

Question

我编写了一个函数，它获取两个数字和一个操作（字符串），并使用给定的操作返回两个数字的结果。例如，calculate_matehamatical_expression（5,6，＆＃39; +＆＃39;）应返回11.我将赋值除以小函数，但是当我调用这些小函数时，它总是返回None。有人可以向我解释为什么会这样吗？这是我写的代码：

def mathematical_sum(num1,num2):
    return num1 + num2

def mathematical_difference(num1,num2):
    return num1 - num2

def mathematical_product(num1,num2):
    return num1 * num2

def mathematical_division(num1,num2):
    if num2 != 0:
        return num1 / num2
    else:
        return None

def operation_error(operation):
    if operation != "+" or operation != "-" or operation != "*" or operation != "/":
        return None




def calculate_mathematical_expression(num1,num2,operation):
    if operation == "+":
        mathematical_sum(num1,num2)
    elif operation == "-":
        mathematical_difference(num1,num2)
    elif operation == "*":
        mathematical_product(num1,num2)
    elif operation == "/":
        mathematical_division(num1,num2)
    else:
        operation_error(operation)

Answer 1

您需要在calculate_mathematical_expression内再次返回，例如：

def calculate_mathematical_expression(num1,num2,operation):
    if operation == "+":
        return mathematical_sum(num1,num2)

mathematical_sum中的回复并不会影响其被调用的功能。

Answer 2

您需要return

当您从某个函数return时，它只会返回到调用它的函数。因此当您return中的mathematical_sum()时，会返回该值至calculate_mathematical_expression()＆amp;你需要从这个函数再次返回，如下所示：

if operation == "+":
    return mathematical_sum(num1,num2)
elif operation == "-":
    return mathematical_difference(num1,num2)
elif operation == "*":
    return mathematical_product(num1,num2)
elif operation == "/":
    return mathematical_division(num1,num2)
else:
    return operation_error(operation)

...否则calculate_mathematical_expression()会返回None。

operation_error()不起作用

• 使用and代替or。否则您的情况将始终为True
• 返回布尔值，而不是None。此处，您的函数始终返回None

示例：

def operation_error(operation):
    return operation != "+" and operation != "-" and operation != "*" and operation != "/"

您不需要operation_error()

由于每个操作员都有条件，因此不需要operation_error()功能，您可以直接执行此操作：

else:
    return None

...甚至删除else语句，让calculate_mathematical_expression()在到达结尾时自动返回None。

Answer 3

您的calculate_mathematical_expression函数未返回任何内容。请尝试以下代码：

def calculate_mathematical_expression(num1,num2,operation):
    if operation == "+":
        return mathematical_sum(num1,num2)
    elif operation == "-":
        return mathematical_difference(num1,num2)
    elif operation == "*":
        return mathematical_product(num1,num2)
    elif operation == "/":
        return mathematical_division(num1,num2)
    else:
        return operation_error(operation)