Open Mind Tree

Most of the games in this book will have simple text for input and output. The input is typed by the user on the keyboard and entered to the computer. The output is the text displayed on the screen. In Python, theprint() function can be used for displaying textual output on the screen. We've learned how the basics of using the print() function, but there is more to learn about how strings and print() work in Python.

Here is the source code for our short jokes program. Type it into the file editor and save it as jokes.py. If you do not want to type this code in, you can also download the source code from this book's website at the URLhttp://inventwithpython.com/chapter5.

Important Note! Be sure to run this program with Python 3, and not Python 2. The programs in this book use Python 3, and you'll get errors if you try to run them with Python 2. You can click on Help and then About IDLE to find out what version of Python you have.

Don't worry if you don't understand everything in the program. Just save and run the program. Remember, if your program has bugs in it, you can use the online diff tool at http://inventwithpython.com/chapter5.

Let's look at the code more carefully.

Here we have three print() function calls. Because we don't want to tell the player what the joke's punch line is, we have a call to the input() function after the first print(). The player can read the first line, press Enter, and then read the punch line.

The user can still type in a string and hit Enter, but because we aren't storing this string in any variable, the program will just forget about it and move to the next line of code.

The last print() function call has no string argument. This tells the program to just print a blank line. Blank lines can be useful to keep our text from being bunched up together.

In the first print()above, you'll notice that we have a slash right before the single quote (that is, the apostrophe). This backslash ( \ is a backslash, / is a forward slash) tells us that the letter right after it is an escape character. An escape character helps us print out letters that are hard to enter into the source code. There are several different escape characters, but in our call to print() the escape character is the single quote.

We have to have the single quote escape character because otherwise the Python interpreter would think that this quote meant the end of the string. But we want this quote to be a part of the string. When we print this string, the backslash will not show up.

What if you really want to display a backslash? This line of code would not work:

That print() function call would show up as:

This is because the "t" in "teal" was seen as an escape character since it came after a backslash. The escape character t simulates pushing the Tab key on your keyboard. Escape characters are there so that strings can have characters that cannot be typed in.

Instead, try this line:

Here is a list of escape characters in Python:

Strings don't always have to be in between single quotes in Python. You can also put them in between double quotes. These two lines print the same thing:

But you cannot mix quotes. This line will give you an error if you try to use them:

I like to use single quotes because I don't have to hold down the shift key on the keyboard to type them. It's easier to type, and the computer doesn't care either way.

But remember, just like you have to use the escape character \' to have a single quote in a string surrounded by single quotes, you need the escape character \" to have a double quote in a string surrounded by double quotes. For example, look at these two lines:

Did you notice that in the single quote strings you do not need to escape double quotes, and in the double quote strings you do not need to escape single quotes? The Python interpreter is smart enough to know that if a string starts with one type of quote, the other type of quote doesn't mean the string is ending.

Did you notice the second parameter on line 15's print()? Normally, print() adds a newline character to the end of the string it prints. (This is why a blank print() function will just print a newline.) But theprint() function can optionally have a second parameter (which has the name end.) The blank string we are passing is called a keyword argument. The end parameter has a specific name, and to pass an argument to this specific parameter we need to use the end= syntax.

Notice that when you type the keyword and the keyword argument, you use only one = sign. It is end='', and not end==''.

By passing a blank string for the end we tell the print() function to not add a newline at the end of the string, but instead add a blank string. This is why '-MOO!' appears next to the previous line, instead of on its own line. There was no newline printed after the 'Interrupting cow wh' string.

This chapter explores the different ways you can use the print() function. Escape characters are used for characters that are difficult or impossible to type into the code with the keyboard. Escape characters are typed into strings beginning with a backslash \ followed by a single letter for the escape character. For example, \n would be a newline. To include a backslash in a string, you would use the escape character \\.

The print() function automatically appends a newline character to the end of the string we pass it to be displayed on the screen. Most of the time, this is a helpful shortcut. But sometimes we don't want a newline character at the end. To change this, we pass the end keyword argument with a blank string. For example, to print "spam" to the screen without a newline character, you would call print('spam', end='').

By adding this level of control to the text we display on the screen, we have much more flexible ways to display text on the screen the exact way we want to.