Input

Python allows you to take input directly from the user using the input function. Let's use it to improve our weather application by asking for the weather before displaying the output.

weather = input("What is the weather like today? ")

if weather == "sunny":
    print("Bring your shades")
elif weather == "rainy":
    print("Bring your umbrella")
elif weather == "snowy":
    print("Bring your wooly muffler")
else:
    print("I don't know what you should bring! I'm just a little program...")

When you run this program, Python should ask you for some input with the prompt What is the weather like today? (The space before the second " makes the prompt look more tidy in the console.) It will then return some advice based on the input.

Asking repeatedly

What if we want Python to keep asking for input instead of exiting after the first question is answered? For that, we can use somethign called a while loop.

Remember our for loop? Instead of iterating through a list like the for loop, our while loop will continue to execute as long as a certain condition is true. Here's a very simple while loop that will run forever until you quit it manually. (Note: if you're using IPython, this may crash your notebook. It's safe to use in your terminal.)

while True:
    print("Oh no! I'm stuck...")

If you're in the terminal, you can escape from this endless loop by pressing Control-c on your keyboard. In IPython, you can stop it by pressing the square STOP button in the toolbar.

Let's apply the while loop to our weather app:

while True:
    weather = input("What is the weather like today? ")

    if weather == "sunny":
        print("Bring your shades")
    elif weather == "rainy":
        print("Bring your umbrella")
    elif weather == "snowy":
        print("Bring your wooly muffler")
    else:
        print("I don't know what you should bring! I'm just a little program...")

Notice that we had to shift everything over one tab to fit it in the while block. Now our program will ask us for input again and again, and give us different answers each time.

Let's add one more feature: an elif statement that will break us out of the loop and end the program:

while True:
    weather = input("What is the weather like today? ")

    if weather == "sunny":
        print("Bring your shades")
    elif weather == "quit":
        break
    elif weather == "rainy":
        print("Bring your umbrella")
    elif weather == "snowy":
        print("Bring your wooly muffler")
    else:
        print("I don't know what you should bring! I'm just a little program...")

The break command ends the current loop early, ending the program when "quit" is given as input.