Being able to print things (on the screen for example) is a fundamental part of interacting with a programming language. So far, we’ve kept it simple by passing the data we want to print directly to print() using the fact that if you pass multiple arguments then it will print each of them, separated by spaces, combining our data with a message:
format.py
my_num =42print("My num is", my_num)
My num is 42
This works perfectly well but you are using the implicit space that’s added by print as part of your sentence. What we can do instead is create a string which contains the message we want to print and put special placeholders inside it where we want our data to appear. There’s a few different ways to do this in Python (an older but still valid method you may see uses % and another uses a format() function) but for this course we will use the method called f-strings which was introduced in Python 3.6 (released December 2016).
If you put a single f directly in front of the string that you are creating, it will enable a special string mode which lets you place {} inside the string with a variable name between the curly brackets {}:
format.py
answer =42pi =3.14159print(f"The answer is {answer} and pi is {pi}")
The answer is 42 and pi is 3.14159
We call this process of substituting values of variables into placeholders string interpolation, and you can have as many interpolations in a string as you like.
Exercise
For many of the exercises here, we are going to be working on some Python code which converts to and from Morse Code. In each section we will add or change the code so make sure that you don’t skip any exercises.
Copy the following code in the text editor into a script called encode.py and run it in the terminal with python encode.py or python3 encode.py to check that it works.
encode.py
letter_to_morse = {'a':'.-', 'b':'-...', 'c':'-.-.', 'd':'-..', 'e':'.', 'f':'..-.', 'g':'--.', 'h':'....', 'i':'..', 'j':'.---', 'k':'-.-', 'l':'.-..', 'm':'--', 'n':'-.', 'o':'---', 'p':'.--.', 'q':'--.-', 'r':'.-.', 's':'...', 't':'-','u':'..-', 'v':'...-', 'w':'.--', 'x':'-..-', 'y':'-.--', 'z':'--..','0':'-----', '1':'.----', '2':'..---', '3':'...--','4':'....-','5':'.....', '6':'-....', '7':'--...', '8':'---..','9':'----.', ' ':'/'}message ="please help"# `morse` is a list which will eventually contain the # strings for each morse code letter in the message.morse = []for letter in message: morse_letter = letter_to_morse[letter] morse.append(morse_letter)# We need to join together Morse code letters with spacesmorse_message =" ".join(morse)print(f"Incoming message: {message}")print(f" Morse encoded: {morse_message}")
Answer
The following code should be put into a file called encode.py using the text editor in JupyterLab:
encode.py
letter_to_morse = {'a':'.-', 'b':'-...', 'c':'-.-.', 'd':'-..', 'e':'.', 'f':'..-.', 'g':'--.', 'h':'....', 'i':'..', 'j':'.---', 'k':'-.-', 'l':'.-..', 'm':'--', 'n':'-.', 'o':'---', 'p':'.--.', 'q':'--.-', 'r':'.-.', 's':'...', 't':'-','u':'..-', 'v':'...-', 'w':'.--', 'x':'-..-', 'y':'-.--', 'z':'--..','0':'-----', '1':'.----', '2':'..---', '3':'...--', '4':'....-','5':'.....', '6':'-....', '7':'--...', '8':'---..', '9':'----.', ' ':'/'}message ="please help"# `morse` is a list which will eventually contain the # strings for each morse code letter in the message.morse = []for letter in message: morse_letter = letter_to_morse[letter] morse.append(morse_letter)# We need to join together Morse code letters with spacesmorse_message =" ".join(morse)print(f"Incoming message: {message}")print(f" Morse encoded: {morse_message}")