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This chapter is from the book

This chapter is from the book

Putting in a Print Message

What if I want the function to not just return a number but to instead print out a user-friendly message such as the following:

7.5 inches are equal to 19.05 centimeters.

I can easily do that in Python. All I need to do is add a call to the built-in print function. Because print is a built-in function of Python, it’s one that you do not define yourself; it’s already defined for you. Here’s a sample of this function in action:

>>>print(’My name is Brian O.’)
My name is Brian O.

Why did I place single-quotation marks around the message to be printed? I did that because this information is text, not numeric data or Python code; it indicates that the words are to be printed out exactly as shown. Here are some more examples:

>>>print(’To be or not to be.’)
To be or not to be.
>>>print(’When we are born, we cry,’)
When we are born, we cry,
>>>print(’That we are come’
    ’ to this great stage of fools.’)
That we are come to this great stage of fools.

The ability to use print pays off in a number of ways: I can intermix text—words placed in quotation marks—with variables.

>>>x = 5
>>>y = 25
>>>print(’The value of’, x, ’squared is’, y)
The value of 5 squared is 25

By default, the print function inserts an extra blank space between one item and the next. Also, after a call to the print function is finished, then by default it prints a newline character, which causes the terminal to advance to the next line.

Now let’s combine the printing ability with the power to define functions.

>>>def convert(x):
    c = x * 2.54
    print(x, ’inches equal’, c, ’centimeters.’)

>>>convert(5)
5 inches equal 12.2 centimeters.
>>>convert(10)
10 inches equal 25.4 centimeters.

Do you now see why the print function is useful? I can call this built-in function from within a definition of one of my functions; that enables my functions to print nice output messages rather than just producing a number.

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