Captain Code: Unleash Your Coding Superpower with Python by Shmuel Forta & Ben Forta

Author:Shmuel Forta & Ben Forta [Shmuel Forta]
Language: eng
Format: epub
Publisher: Addison-Wesley Professional
Published: 2021-12-24T16:00:00+00:00

Returning Values

Now you know how to create a function and how to pass it arguments. The last thing we need to look at is how to return values from a function.

Functions can return values. Think about how you used input(). It interacted with the user and then returned whatever the user typed as the result. upper() returns the uppercase version of a string. now() returns today’s date and time.

Your own functions will frequently need to be able to return values, too, and you can do this with the (very conveniently named) return statement.

Let’s look at an example—and a very useful example at that. You know what this code does, right?

num=input("Enter a number: ")

This code asks the user to Enter a number: and then stores whatever they typed into a variable named num.

So, if the user typed abc (which is definitely not a number), that will be saved into variable num. Not good.

So, here’s a better version of the code:

Click here to view code image

num=inputNumber("Enter a number: ")

This version calls a function named inputNumber() instead of input(). Unlike input(), which will accept any text, inputNumber() is smart and makes sure the user actually types a number. Cool, huh?

Well, it would be if the inputNumber() function actually existed. But, alas, it doesn’t.

But, there’s a solution. We can create the function ourselves. Here’s the code for Func4.py:

Click here to view code image

# Numeric input function def inputNumber(prompt): # Input variable inp = "" # Loop until variable is a valid number while not inp.isnumeric(): # Prompt for input inp = input(prompt).strip() # Return the number return int(inp) # Get a number num=inputNumber("Enter a number: ") # Display it print(num)

Save and run the code. It will prompt you for a number, which will then be displayed. If you don’t type a number, it’ll keep asking you to Enter a number, and won’t stop until you actually enter a number.

The last two lines of code are pretty simple. inputNumber() works just like input(). It accepts a prompt and returns a value. Here the value is saved to a variable named num, which is then printed.

The real magic is the inputNumber() function itself. We start by defining it:

# Numeric input function def inputNumber(prompt):

Just like input(), inputNumber() accepts a prompt—the text that is displayed to the user—and the prompt is passed as an argument.

Next, the code defines a variable that will store the user input:

# Input variable inp = ""

Then comes the actual prompt inside of a loop:

Click here to view code image

# Loop until variable is a valid number while not inp.isnumeric(): # Prompt for input inp = input(prompt).strip()

This is code you’ve seen before. It uses a while loop with a condition that ensures that the loop will keep looping until inp is a number.

The actual input() is the same one we’ve been using throughout this book. What text does input() display as a prompt? Whatever gets passed to ­inputNumber() as an argument. prompt is a passthrough variable: You pass it to our UDF ­inputNumber(), which passes it to the built-in function input().

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