Script, Input & Output

Until now, we’ve been interacting directly in Python’s interpreter. We can keep using it from time to time to test some specific code but as of now, we will program in the text editor and only then execute it in the interpreter.

Script

We are going to create a script that calculates the perimeter and the area of a rectangle based on its length and width.

1. Open Thonny.
2. Write the below code in the script window (above the interpreter).
   🐍 Python Script

   length = 5
   width = 3
   perimeter = 2 * width + 2 * length
   area = width * length
   (area, perimeter)
   

3. Save your file and name it rectangle.py.

4. Go to the tab Run and click on Run current script

   The below result should appear in the interpreter:

   📋 Output

   >>> %Run rectangle.py
   >>> 
   

   It does not show an error, everything worked well.

Question

Why do we not see any result? Should we not see the value of the perimeter and the area of the rectangle?

Answer

As of the moment we use scripts, if we want to communicate with the user and show results on the screen, we need to use an output function: print().

Output

The print() function prints whatever is written between the parenthesis to the screen. Let's improve our previous script so we can show to the user the results of our calculations.

1. Update your code:

   🐍 Python Script

   length = 5
   width = 3
   perimeter = 2 * width + 2 * length
   area = width * length
   print(area, perimeter)
   

   Info

   No need to rewrite everything, just add print at the beginning of row 5.

2. Go to the tab Run and click on Run current script.

   The below result should appear in the interpreter:

   📋 Output

   >>> %Run rectangle.py
   15 16
   >>>  
   

3. Let's add some text in our print so the message is clearer.

🐍 Python Script

    length = 5
    width = 3
    perimeter = 2 * width + 2 * length
    area = width * length
    print("Area:", area, "Perimeter:", perimeter)

Very nice, you can now easily share information with the user.

Question

What if we want the user to choose the length and width of the rectangle?

Answer

If we want the user to communicate with the computer and give some information, we need to use an input function: input()

Input

The function input() will allow our script to ask a question to the user. It will interrupt the execution of the program and wait for the input from the user. Then you can save the given answer in a variable and reuse it later on.

input() accepts one optional parameter: the message that will be shown to the user.

The type of data returned by this function will always be a string. If you want to receive a float or an integer from the user, you have to specify it.

Example

IntegerFloatString

🐍 Python Script

numberOfChildren = int(input("How many children do you have? "))

🐍 Python Script

temperature = float(input("What is the temperature? "))

🐍 Python Script

name = input("What is your name? ")

Let's improve our previous script by asking the width and length to the user.

1. Update your code:

   🐍 Python Script

   length = float(input("Give me a length: "))
   width = float(input("Give me a width: "))
   perimeter = 2 * width + 2 * length
   area = width * length
   print("Area:", area, "Perimeter:", perimeter)
   

   Info

   No need to rewrite everything, just add the input on the right side of the assignation = for length and width.

2. Go to the tab Run and click on Run current script.

   The below result should appear in the interpreter:

   📋 Output

   >>> %Run rectangle.py
   Give me a length: 8
   Give me a width: 9
   Area: 72.0 Perimeter: 34.0
   >>>