I am building a temperature conversion module called Unico. Now, when I want to convert kelvin to fahrenheit or fahrenheit to kelvin, it makes a calculation error. Of course, there is no problem when the input number is non-decimal.
What’s the problem??

preunit,nextunit = prenext.split(' ')

prenum = int(prenum)

if preunit == 'c' and prenum>=(-273.15):

    if nextunit == 'k':

        return round(prenum + 273.15,2)

    if nextunit == 'f':

        return round(prenum * 1.8 + 32,2)

elif preunit == 'k' and prenum>=0:

    if nextunit == 'c':

        return round(prenum - 273.15,2)

    if nextunit == 'f':

        if prenum == 0:

            return -459.67

        return round(((prenum-273.15)*1.8)+32,2)

elif preunit == 'f' and prenum>=-459.67:

    if nextunit == 'c':

        return round((prenum - 32)/1.8,2)

    if nextunit == 'k':

        return round(((prenum - 32)/1.8)+273.15,2)

else:

    return 'Unit Not Found!'`

The problem is from k to f and f to k.