Скачать или смотреть How to Transform PyXdmValue into Python-Native Types Using XQuery

Learn how to convert XQuery results from Saxon-C's `PyXdmValue` into native Python data types with clear examples and code snippets.
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This video is based on the question https://stackoverflow.com/q/77630986/ asked by the user 'N Raghu' ( https://stackoverflow.com/u/5747326/ ) and on the answer https://stackoverflow.com/a/77631249/ provided by the user 'Martin Honnen' ( https://stackoverflow.com/u/252228/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you're working with XQuery to extract data from XML files in Python using Saxon-C, you might encounter a challenge when dealing with the output type known as PyXdmValue. Instead of receiving the data in familiar Python-native formats, you're left with an object that represents an XDM sequence of items. This guide aims to help you understand how to convert these PyXdmValue responses into native Python types, making your data manipulation tasks much more intuitive.

The Problem

When executing an XQuery query, the result typically returns as a PyXdmValue type like this:

[[See Video to Reveal this Text or Code Snippet]]

This representation can be confusing and inconvenient if you're expecting to work with standard Python data types, such as dictionaries or lists. Therefore, it's essential to know how to convert these values appropriately.

Understanding PyXdmValue

A PyXdmValue represents a sequence of XDM items that may vary in type. These XDM items can be:

XDM nodes (elements and attributes)

XDM atomic values (strings, booleans, numbers, date/time types)

Function items (including maps and arrays)

The structure of the result will depend on your XQuery, making it necessary to handle various item types accordingly.

Example XQuery

Consider the following XQuery, which calculates the average population for cities in a country and returns the data as an XDM map with string keys and double values:

[[See Video to Reveal this Text or Code Snippet]]

Converting PyXdmValue to Python Types

Now, let's discuss how to convert the PyXdmValue to Python native types, focusing on two primary use cases.

Converting an XDM Map to a Python Dictionary

When your XQuery result is an XDM Map, you can easily convert it into a dictionary using dictionary comprehension. Here’s how:

[[See Video to Reveal this Text or Code Snippet]]

Expected Output:

[[See Video to Reveal this Text or Code Snippet]]

Converting a Sequence of XML Elements to a Python List

If you're retrieving a sequence of XML elements, you can convert it to a Python list in one of two ways: extracting string values or serializing the elements.

Here’s how to do both:

[[See Video to Reveal this Text or Code Snippet]]

Expected Output:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Dealing with PyXdmValue output in Python can be daunting, but with a clear understanding and a few code examples, you can easily convert XDM values into native types that are much easier to work with. Whether you're transforming an XDM map into a dictionary or extracting string values from XML elements, the key is to understand the structure of the data you're receiving and apply the appropriate conversion methods.

Now that you have the tools to handle PyXdmValue effectively, you can make your data processing tasks smoother and more efficient!