Temperature Converter

Since 1960, the International System of Units (or SI, short for Système international) has been in place. This system is used in nearly every country, standardizing the units of measurement for science, technology, industry and everyday life. In this system, there are standard units for measurements for amongst others time (seconds), length (meters), electric current (ampere) and temperature.

Where most quantities have only one unit of measurement, temperature is a little different. The SI prescribes that temperature has the unit of measurement of Kelvin, but in practice it is common to use other units of measurement. In most of the world, Celsius (centigrade) is preferred in everyday life as this allows for more manageable and understandable numbers than Kelvin.

It is thus very important to be able to convert temperature measured in Kelvin to Celsius, and what better way to do this than to use Python! Whereas Kelvin’s zero point (0 K) is defined by the absolute zero of temperature, Celsius’ zero point (0 °C) is defined by the freezing point of water. In Celsius, the absolute zero of temperature is −273.15 °C, which is also the offset between the two scales.

Now that we know how to ask the user for input, let’s create a script `kelvin_to_celsius.py` that asks the user to input a temperature in Kelvin and outputs that temperature in Celsius.

You have hopefully already seen that once we start asking the user to give input, there are many more things that can go wrong. It is always possible that a user gives an input you did not expect and that is not compatible with the code you have written. If we do not check if the user inputs the right thing (in our case, a number), the script will crash. To prevent this we need to implement something called input validation, a crucial part of the security and functionality of almost any application with user input. Implement basic input validation using a string method and an if-statement to check whether the input was actually a digit. If not, fail gracefully by showing the user the error `“Please input a digit.”`.