1.7 Itse1359-1040-strings part 1  (Page 4/6)

Escape sequences

Escape sequences are special sequences of characters used to represent other characters that

• cannot be entered directly into a string, or
• would cause a problem if entered directly into a string.

The newline character

An example of a character that cannot be entered directly into a string is the newline character. Except when using triple quoted strings, you cannot enter the newline character directly into astring.

Why? Because when you press the Enter key in an attempt to enter a newline, that simply terminates your input for that line. It doesn't enter thenewline character into the string.

The interactive code fragment in Figure 4 illustrates the use of an escape sequence to enter the newline character into a string. Note the \n between my first and last names.

The built-in print function

The Python interpreter has a number of functions built into it that are always available. They are listed in The Python Standard Library -- 2. Built-in Functions in alphabetical order. One of those functions is the print function.

The code in Figure 4 calls the print function to display my name on two output lines.

When the print function is used interactively, it is a request to have its argument (the expression in parentheses) printed on the next line. In Figure 4 , it is a request to have my name printed on the next line.

Including the newline character

In Figure 4 , I entered the newline escape sequence between my first and last names when I constructed the string. Then, when the string was printed, thecursor advanced to a new line following my first name and printed my last name on the new line. That is what escape sequences are all about.

The print function renders according to meaning

Note that the print function rendered the newline character according to its meaning.

By this, I mean that the print function did not print something that represented the newline character (\n) as we saw in Figure 3 . Instead, it actually did what a newline character is supposed to do -- go to the beginningof the next line.

The quote character

Escaping the quote character

Suppose that you are constructing a string that is surrounded by double quotes, and you want to use a pair of double quotes inside the string. If youwere to simply enter the double quote when you construct the string, that quote would terminate the string.

The interactive code fragment in Figure 5 shows how to escape the double quote character -- precede it with a backslash character.

What I mean by this is that if you want to include a double quote inside a string that is surrounded by double quotes, you must enter the double quoteinside the string as shown in Figure 5 .