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Python Input and Output (IO)

Output 

print('Hello!')

Hello!

We know we can use the print() function to show information on the screen.

We can also show the value (data) stored in a variable such as:

name = 'John Paul'
print(name)

John Paul

The print() function can also display multiple things at one time:

print(name, "how are you?")

John Paul how are you?

Notice that with multiple values, they are separated by a space ' ', which is called the separator. We can actually change the separator with the sep= parameter in the print() function.

An example of print with a sep (separator) specified:

print(name, "how are you?", sep=', ')

John Paul, how are you?

This is basic python output -- it is the output from the computer to the user (person) who can see it by using the output device (e.g. looking at the screen).

Input

How does the user -- the person who uses your program -- enter data into the program? The input() function in Python does just that.

For example:

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

The input function first displays a message (prompt) What is your name? and waits for the user to type. Once the user enters something and presses the Eneter key, the input data (e.g. letters of a name) will be stored in the name variable.

Remember, with the assignment operator =, the statement here is to take the value on the right (input) and store it in the variable on the left (name).

Now if you use:

print("You entered: ", name)

It shows what the user just typed in and has been stored in the variable name.

Example Program: Knock-knock

Python Program

The Game (Algorithm)

Consider a knock-knock joke, it consists of the following steps between two persons, say John and Mary:

  1. John pretends to knock on the door, saying, "Knock knock."
  2. Mary responds with "Who is there?"
  3. John answers with a name, e.g. "Boo"
  4. Mary is confused by the name and continue to ask in a pattern like "name who?", e.g. "Boo who? "
  5. The final response depends on the joke and can be difficult to program. For now, let's simply repeats it by saying "Don't cry!"

An example knock-knock:

  1. John: Knock knock!
  2. Mary: Who is there?
  3. John: Boo.
  4. Mary: Boo who? (sounds like Boohoo...)
  5. John: Please don't cry...

The Program Code

Suppose John is the user who will play with the program, here is the simple Python code:

print("John: Knock knock.")
print("Mary: Who is there? ")
name = input("Enter your response: ")
print("Mary:", name, "who?") # sounds like name hoo...
print("John: Please don't cry...")