5. The print Function

5.1. Printing Hello World

We will use a function called print to print to the screen. print is called a function.

You’ve already used functions in mathematics. For example, sin and cos. Functions are followed by parentheses: ( ). We put the function parameter(s) inside the parenthesis.

With a sine function, we put in an angle. With the print function, we are going to put the text we want to print. Text must be enclosed in quotes.

print("Hello there")

Note that case matters. The following will not work:

Print("Hello there")

Great! Time to run it. Right-click on the program and select “Run ‘lab_01.py’”

Before we go on, note how the PyCharm window is put together. See the output of your program at the bottom of the screen. Click the image below to make it bigger and note the:

  • Right margin. You can write code past this point, but don’t.
  • Where you can hover your mouse for “hints” on how to make your code better.
  • Where you can quickly click to run your program again.
../../_images/pycharm_window.png

Ok, now it’s time to update our program. Go back to our program and improve it by printing multiple lines, while quoting Snoopy’s famous story:

5.2. Multiple Print Lines

Let’s add additional code:

print("It was a dark and stormy night.")
print("Suddenly a shot rang out!")

Go ahead and run it to make sure it outputs as expected.

5.3. Escape Codes

If quotes are used to tell the computer the start and end of the string of text you wish to print, how does a program print out a set of double quotes? (This is a double quote " and this is a single quote '.) For example:

print("I want to print a double quote " for some reason.")

This code doesn’t work. The computer looks at the quote in the middle of the string and thinks that is the end of the text. Then it has no idea what to do with the commands for some reason and the quote and the end of the string confuses the computer even further.

It is necessary to tell the computer that we want to treat that middle double quote as text, not as a quote ending the string. This is easy, just prepend a backslash in front of quotes to tell the computer it is part of a string, not a character that terminates a string. For example:

print("I want to print a double quote \" for some reason.")

This combination of the two characters \" is called an escape code. Almost every language has escape codes. Here’s another example:

print("Audrey Hepburn once said \"Nothing is impossible. The word itself says 'I'm Possible!'.\"")

This will print:

Audrey Hepburn once said "Nothing is impossible. The word itself says 'I'm Possible!'."

Because the backslash is used as part of an escape code, the backslash itself must be escaped if you want to use one. For example, this code does not work correctly:

print("The file is stored in C:\new folder")

Why? Because \n is an escape code. To print the backslash it is necessary to escape it like so:

print("The file is stored in C:\\new folder")

There are a few other important escape codes to know. Here is a table of the important escape codes:

Escape code Description
\' Single Quote
\" Double Quote
\t Tab
\r CR: Carriage Return (move to the left)
\n LF: Linefeed (move down)

What is a “Carriage Return” and a “Linefeed”? Try this example:

print("This\nis\nmy\nsample.")

The output from this command is:

This
is
my
sample.

The \n is a linefeed. It moves “cursor” where the computer will print text down one line. The computer stores all text in one big long line. It knows to display the text on different lines because of the placement of \n characters.

To make matters more complex, different operating systems have different standards on what makes a line ending.

Escape code Description
\r\n CR+LF: Microsoft Windows
\n LF: UNIX based systems, and newer Macs.
\r CR: Older Mac based systems

Ok, now it is time to make this lab yours. Write program that consists of several print statements. Here is my example:

print("You can print a statement surrounded by double quotes.")
print('You can print a statement surrounded by single quotes.')

print("If you want to print a double quote, you can by prepending it with")
print("a slash. \"That's great!\" he said.")

print("If you want to print a backslash, you can by prepending it with")
print("a slash. So this \\ prints one backslash, and this \\\\ does two.")

print("You can print a blank line with a empty print statement.")
print()

print("You can use a backlash n to print a new line. These\nare\non\nnew\nlines.")
print("""You can print
on multiple
lines using
triple
quotes. Just in
case you wanted to.""")