如何让Python使用raw_input值作为固定点数？

Question

I'm making a unit converter just to practice. Currently, I've defined a function to figure out what type of conversion to make (distance, time, mass, etc.).

It then calls the correct converter for the type, asks what you're converting from, what you're converting to, and what the value for conversion is.

def mass_converter():
    convert_from = raw_input('What unit are you converting from? ')
    convert_to = raw_input('What unit are you converting to? ')
    value = raw_input('How many of those do you have? ')

    if convert_from == "pounds" and convert_to == "kilograms":
        answer = float(value) * 0.453592
        print "That many pounds is %d kilograms." % answer
    elif convert_from == "kilograms" and convert_to == "pounds":
        answer = float(value) * 2.20462
        print "That many kilograms is %d pounds." % answer
    else:
        print "You have not selected a valid unit; please try again."
        mass_converter()

Currently, if I were to convert 10 pounds to kilograms, it tells me that the answer is 4 kilograms. It seems to be chopping off my decimals. Obviously int(value) will do the same thing. What can I use to keep the exact value entered by the user?

Answer 1

The problem here is that you're using the %d format modifier in your string formatting which casts your answer to an integer. Use %f instead (or even %s ).

Answer 2

You could use %f instead of %d. %d formats the number not as a floating point, but as a integer. Alternatively you could use

  print "That many kilograms is {} pounds.".format(answer)