According to the preface, what is the policy for using code examples from this book?

The book generally permits you to use code examples in your programs and documentation without requesting permission, unless you are reproducing a significant portion of the code or selling or distributing examples from O'Reilly books. Attribution is appreciated but not required.

The policy states that example code accompanying the book may be used in your own programs and documentation without contacting the publisher, except where you are reproducing a significant portion of the code. Selling or distributing O'Reilly examples requires permission, as does incorporating a large amount of example code into your product's documentation. Citing the book and quoting example code in an answer does not require permission. Attribution, including title, author, publisher, and ISBN, is appreciated but generally not required. If your use falls outside fair use or these permissions, you are encouraged to contact permissions@oreilly.com.