对在类中调用方法感到困惑（PYTHON）

Question

So i've got a class for dealing with temperatures, it's really basic, but for some reason the conversion of celsius to fahrenheit is failing to return a correct result in one area of the class when it works otherwise.

I'm writing the add method, and in order to add two temperatures of different types, they have to be converted. I have a method for switching between celsius and fahrenheit, and it works when I just do that in a test program:

Testing celsius method:
Converting to celsius...
Result: Temperature: -12.222222222222221 degrees C

Testing fahrenheit method:
Converting back to fahrenheit...
Result: Temperature: 10.0 degrees F

But, if I try to use this to add two different types (extra prints to see what it's doing):

def __add__( self, other ):

    if type( other ) != Temperature:
        other = Temperature( other )

    a_scale = self.__scale

    if a_scale == 'F':
        print(self)
        print(other)
        temp_1 = self.fahrenheit()
        temp_2 = other.fahrenheit()
        print(temp_1)
        print(temp_2)
        temp_3 = temp_1.__magnitude + temp_2.__magnitude
        return Temperature( temp_3, 'F' )

    elif a_scale == 'C':
        print(self)
        print(other)
        temp_1 = self.celsius()
        temp_2 = other.celsius()
        print(temp_1)
        print(temp_2)
        temp_3 = temp_1.__magnitude + temp_2.__magnitude
        return Temperature( temp_3, 'C')

It will print out that it converted 10 degrees C to 68 degrees F (???)

output:

Testing addition
Temp 2 = Temperature: 20 degrees C
Performing temp1 + temp2...
Temperature: 10 degrees F
Temperature: 20 degrees C
Temperature: 10 degrees F
Temperature: 68.0 degrees F
Temperature: 78.0 degrees F

This is the fahrenheit method:

def fahrenheit( self ):

    if self.__scale == 'F':
        return Temperature( self.__magnitude, 'F')
    elif self.__scale == 'C':
        f = ((self.__magnitude * 9) / 5) + 32
        return Temperature( f, 'F' )

And it works perfectly fine as far as I can tell.

Celsius, which is almost identical:

def celsius( self ):

    if self.__scale == 'C':
        return Temperature( self.__magnitude, 'C')
    elif self.__scale == 'F':
        c = ((self.__magnitude - 32) * 5) / 9
        return Temperature( c, 'C' )

I can't for the life of me figure out why this is happening :(

Answer 1

You seem to be misreading the output of your own program. The values outputted are:

Temperature: 10 degrees F    # self
Temperature: 20 degrees C    # other
Temperature: 10 degrees F    # temp_1 = self.fahrenheit()
Temperature: 68.0 degrees F  # temp_2 = other.fahrenheit()
Temperature: 78.0 degrees F  # The sum of the above two

Thus, 10°F becomes 10°F, and 20°C becomes 68°F, which is correct.

Answer 2

I guess, the reason is whole number arithmetic. Try ((self.__magnitude - 32) * 5) / 9.0 and ((self.__magnitude * 9) / 5.0) + 32 . I've performed a simple test (w/o class stuff, just math) and it gives correct results.