Python & XML

Location Paths

The most commonly used type of XPath expression is the location path. A location path can be thought of as similar to a path for a file on a disk, but on steroids. Where a path for a filesystem contains only names of directories and a file, an XPath location path can specify much more. At each step along the path, it can perform selection based on complex tests of the nodes in a document, and the result may be several nodes. The tests, or predicates, for each step of the path can match based on element name, attribute presence or value, or textual content.

The full syntax of location paths is complex, but the specification is considerate enough to define abbreviated forms for the most commonly used tests; these are called abbreviated location paths. All of the location paths we describe in this chapter use the abbreviated syntax; for more information on the full syntax and selection capabilities of XPath, please refer to the specification.

Location paths are used within XSLT elements, but may also be used programmatically with an XPath API to return node sets from an XML document at runtime. The latter technique will come into greater focus as you read this chapter; the former is covered in Chapter 6.

An Example Document

Let’s start with an example document that represents data records. The records are all fairly similar, but of course the field values are different in each one. This is typical of the type of documents you might mine with XPath. In Example 5-1, we ...