lxml-dataclass 1.0.0

Create LXML Elements as dataclasses representations

LXML-DATACLASS

Utility to mirror Python Classes with lxml.etree Elements using class annotations and field descriptors.

⚠️ Warning: this package was created to help the owner with big xml file description and manipulation.
Use under your own risk. 

🆘 Help wanted. If you are insterested in continue the development of this package, send me a PM.

Installation

pip install lxml-dataclass

Basic usage

Lxml-dataclass uses big part of dataclasses implementation with some modifications that allow the implemmentation of two utility methods to the classes that inherit from Element base class to_lxml_element and from_lxml_element. Using the element_field function allows the metaclass to keep tracking of many lxml.etree attributes.

Lets start with some basic examples:

from lxml_dataclass import Element, element_field


class Author(Element):
    __tag__ = 'Author'
    
    name: str = element_field('Name')
    last: str = element_field('LastName', default='Doe')

    def fullname(self) -> str:
        return self.name + self.last

author = Author('John')
author.fullname()
# John Doe

As you can see in the given example we defined a class called Author with the attributes name and last as you can see these attributes where defined with their respectives types annotations and the field descriptor function element_field this functions accepts almost the same arguments the original dataclass field function uses except you must give as first argument the tag name the given attribute. The init method is automatically generated and you can overload it.

In the example above the tag for name will be Name and for last will be LastName

Now we will call the to_lxml_element() method to obtain the lxml.etree.Element representing this object

import lxml.etree as ET

author_element = author.to_lxml_element() 
ET.tostring(author_element)
# b'<Author><Name>John</Name><LastName>Doe</LastName></Author>'

The Element class also includes another utility method called to_string_element() which calls the ET.tostring() function on the representing element and accepts the same keyword arguments.

author.to_string_element(pretty_print=True).decode('utf-8')
#<Author>
#  <Name>John</Name>
#  <LastName>Doe</LastName>
#</Author>

Attribs and Nsmap

As you know all lxml Element accetps the attrib and nsmap arguments. For Element classes you will define those attributes on __attrib__ and __nsmap__ class or instance attributes and for class attributes you will define them on the element_field method with the attrib and nsmap key word arguments.

Lets add some attributes:

class Author(Element):
    __tag__ = 'Author'
    __attrib__ = {'ID': 'Test ID'}
    
    name: str = element_field('Name', nsmap={None: 'suffix'})
    last: str = element_field('LastName', default='Doe')

Before we get the element string we will change the ID attribute.

author.__attrib__['ID'] = 'Changed ID'
author.to_string_element(pretty_print=True).decode('utf-8')
#<Author ID="Changed ID">
#  <Name xmlns="suffix">John</Name>
#  <LastName>Doe</LastName>
#</Author>

Class inheritance and composition

Inheritance functions exactly the same as dataclasses so you can inherit from other Element classes within the rules of dataclass and init generation.

Lets create an Element mixin that will add an ID to every instance who inherit it.

from uuid import UUID, uuid4

class HasIDMixin(Element):

    id: UUID = element_field('Id', default_factory=uuid4)


class Author(HasIdMixin, Element):
    __tag__ = 'Author'
    
    name: str = element_field('Name')
    last: str = element_field('LastName', default='Doe')

author = Author('John', 'Mayer')
author.to_string_element(pretty_print=True).decode('utf-8')
#<Author>
#  <Name>John</Name>
#  <LastName>Mayer</LastName>
#  <Id>a6ff6e02-eeb7-4ca5-8e4d-efedc40ee9ae</Id>
#</Author>

Now lets create a book element that will be a child of author

class Book(Element):
    __tag__ = 'Book'

    name: str = element_field('Name')
    pages: int = element_field('Pages', default=50)


class Author(Element):
    __tag__ = 'Author'
    
    name: str = element_field('Name')
    last: str = element_field('LastName', default='Doe')
    book: Book | None = element_field('book', default=None) # Notice the tag is the same as the attribute name

author = Author('John')
book = Book('My cool book', 80)
author.book = book
author.to_string_element(pretty_print=True).decode('utf-8')
#<Author>
#  <Name>John</Name>
#  <LastName>Doe</LastName>
#  <Book>
#    <Name>My cool book</Name>
#    <Pages>80</Pages>
#  </Book>
#</Author>

Now what if we want an Author to have multiple Books. Then we stablish the is_iterable special keyword on element_field function as follows

class Author(Element):
    __tag__ = 'Author'
    
    name: str = element_field('Name')
    last: str = element_field('LastName', default='Doe')
    books: list[Book] = element_field('books', default_factory=list, is_iterable=True) # Notice the tag is the same as the attribute name

Now you could do

author = Author('John')
book_a = Book('My cool book A', 80)
book_b = Book('My cool book B')
author.books.append(book_a)
author.books.append(book_b)
author.to_string_element(pretty_print=True).decode('utf-8')
#<Author>
#  <Name>John</Name>
#  <LastName>Doe</LastName>
#  <Book>
#    <Name>My cool book A</Name>
#    <Pages>80</Pages>
#  </Book>
#  <Book>
#    <Name>My cool book B</Name>
#    <Pages>50</Pages>
#  </Book>
#</Author>

Now you can create really complex xml-class-representations with a simple and known dataclass approach, you can overload the utility methods to suit your needs.