After learning about data structures, user input and output programming becomes a lot more powerful. There are many things that we can accomplish by simply taking user input, running it through a process, and returning some useful output. To put these skills to use, we’ll write a simple tool to perform temperature conversions from Fahrenheit to Celsius.
To feel comfortable completing this lab you’ll want to know how to do the following:
* Handling user input using the `input` function. Watch the videos from the “Input and Output Operations” section of the Certified Entry-Level Python Programmer Certification course.
* Type casting from strings to floats. Watch the “Type Casting” video from the Certified Entry-Level Python Programmer Certification course.
* Printing to the screen. Watch the videos from the “Input and Output Operations” section of the Certified Entry-Level Python Programmer Certification course.
Learning Objectives
Successfully complete this lab by achieving the following learning objectives:
- Create the ~/to-celsius.py Script and Make It Executable with python3.7
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 ourpython3.7binary, 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 hereNow that the file is created, we need to also make it executable by using
chmod:$ chmod u+x ~/to-celsius.pyNow we can run our script by running
./to-celsius.pyfrom our home directory.- Prompt and Store Fahrenheit Value from User
When we run our script, we would like to prompt the user for a temperature value in Fahrenheit. Let’s do this using the
inputfunction:~/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.
- Calculating the Celsius Value
The Fahrenheit to Celsius formula is
celsius = (temp - 32) * 5 / 9and this converts almost perfectly to Python. We only need to changetempto be our variablefahrenheit.~/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 the Calculated Value to the Screen
Now that we have our final value we’re ready to print it to the screen in the form of:
FAHRENHEIT F is CELSIUS CWe can do this by passing our values into the
printfunction:~/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 CWe’re showing more decimal places in our Celsius value than we might like and these can be hidden by using the
roundfunction to round to 2 decimal places like
thisround(celsius, 2).
