Making Calculations from User Input with Python

For the time being, we're going to write our script in our home directory (~) and we want to be able to run it right away. To make sure that we're not completely tied to the path of our python3.7 binary, we need to we set up our shebang properly.

Let's create the file and set the shebang:

~/to-celsius.py

#!/usr/bin/env python3

# Python implementation here

Now that the file is created, we need to also make it executable by using chmod:

$ chmod u+x ~/to-celsius.py

Now we can run our script by running ./to-celsius.py from our home directory.

When we run our script, we would like to prompt the user for a temperature value in Fahrenheit. Let's do this using the input function:

~/to-celsius.py

#!/usr/bin/env python3

# Python implementation here
fahrenheit = input("What temperature (in Fahrenheit) would you like converted to Celsius? ")

By default, this variable will be a string, so we'll need to cast it to be a float:

~/to-celsius.py

#!/usr/bin/env python3

# Python implementation here
fahrenheit = float(input("What temperature (in Fahrenheit) would you like converted to Celsius? "))

Now we're ready to use this value in our calculation.

The Fahrenheit to Celsius formula is celsius = (temp - 32) * 5 / 9 and this converts almost perfectly to Python. We only need to change temp to be our variable fahrenheit.

~/to-celsius.py

#!/usr/bin/env python3

# Python implementation here
fahrenheit = float(input("What temperature (in Fahrenheit) would you like converted to Celsius? "))
celsius = (fahrenheit - 32) * 5 / 9

Now that we have our final value we're ready to print it to the screen in the form of:

FAHRENHEIT F is CELSIUS C

We can do this by passing our values into the print function:

~/to-celsius.py

#!/usr/bin/env python3

# Python implementation here
fahrenheit = float(input("What temperature (in Fahrenheit) would you like converted to Celsius? "))
celsius = (fahrenheit - 32) * 5 / 9
print(fahrenheit, "F is", celsius, "C")

Now if we use our script we should see the following:

$ ./to-celsius.py
What temperature (in Fahrenheit) would you like converted to Celsius? 68.18
68.18 F is 20.100000000000005 C

We're showing more decimal places in our Celsius value than we might like and these can be hidden by using the round function to round to 2 decimal places like this round(celsius, 2).