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Python Architecture for XML Binding

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Python Architecture for XML Binding

paxb is a library that provides an API for mapping between XML documents and Python objects.

paxb library implements the following functionality:

  • Deserialize XML documents to Python objects
  • Validate deserialized data
  • Access and update Python object fields
  • Serialize Python objects to XML documents

paxb provides an efficient way of mapping between an XML document and a Python object. Using paxb developers can write less boilerplate code emphasizing on application domain logic.

Since paxb based on attrs library paxb and attrs API can be mixed together.

Installation

You can install paxb with pip:

$ pip install paxb

Requirements

Documentation

Documentation is available at Read the Docs.

Quick start

Suppose you have an xml document user.xml:

<?xml version="1.0" encoding="utf-8"?>
<doc:envelope xmlns="http://www.test.org"
              xmlns:doc="http://www.test1.org">
    <doc:user name="Alex" surname="Ivanov" age="26">

        <doc:birthdate year="1992" month="06" day="14"/>

        <doc:contacts>
            <doc:phone>+79204563539</doc:phone>
            <doc:email>alex@gmail.com</doc:email>
            <doc:email>alex@mail.ru</doc:email>
        </doc:contacts>

        <doc:documents>
            <doc:passport series="3127" number="836815"/>
        </doc:documents>

        <data:occupations xmlns:data="http://www.test2.org">
            <data:occupation title="yandex">
                <data:address>Moscow</data:address>
                <data:employees>8854</data:employees>
            </data:occupation>
            <data:occupation title="skbkontur">
                <data:address>Yekaterinburg</data:address>
                <data:employees>7742</data:employees>
            </data:occupation>
        </data:occupations>

    </doc:user>
</doc:envelope>

To deserialize the document you could use xml library api to parse the document and then access and modify the parsed xml DOM manually. Such an imperative code has a lot of boilerplate operations that takes a lot of time and can lead to bugs. Instead you can use paxb api to write a declarative style code. All you need to describe field mappings and types, paxb will serialize and deserialize data for you:

import json
import re
from datetime import date

import attr
import paxb as pb


@pb.model(name='occupation', ns='data', ns_map={'data': 'http://www.test2.org'})
class Occupation:
    title = pb.attr()
    address = pb.field()
    employees = pb.field(converter=int)


@pb.model(name='user', ns='doc', ns_map={'doc': 'http://www.test1.org'})
class User:
    name = pb.attr()
    surname = pb.attr()
    age = pb.attr(converter=int)

    birth_year = pb.wrap('birthdate', pb.attr('year', converter=int))
    birth_month = pb.wrap('birthdate', pb.attr('month', converter=int))
    birth_day = pb.wrap('birthdate', pb.attr('day', converter=int))

    @property
    def birthdate(self):
        return date(year=self.birth_year, month=self.birth_month, day=self.birth_day)

    @birthdate.setter
    def birthdate(self, value):
        self.birth_year = value.year
        self.birth_month = value.month
        self.birth_day = value.day

    phone = pb.wrap('contacts', pb.field())
    emails = pb.wrap('contacts', pb.as_list(pb.field(name='email')))

    passport_series = pb.wrap('documents/passport', pb.attr('series'))
    passport_number = pb.wrap('documents/passport', pb.attr('number'))

    occupations = pb.wrap(
        'occupations', pb.lst(pb.nested(Occupation)), ns='data', ns_map={'data': 'http://www.test2.org'}
    )

    citizenship = pb.field(default='RU')

    @phone.validator
    def check(self, attribute, value):
        if not re.match(r'\+\d{11,13}', value):
            raise ValueError("phone number is incorrect")


with open('user.xml') as file:
    xml = file.read()

Then the deserialized object can be modified and serialized back to xml document or converted to json format:

try:
    user = pb.from_xml(User, xml, envelope='doc:envelope', ns_map={'doc': 'http://www.test1.org'})
    user.birthdate = user.birthdate.replace(year=1993)

    with open('user.json') as file:
        json.dump(attr.asdict(user), file)

except (pb.exc.DeserializationError, ValueError) as e:
    print(f"deserialization error: {e}")

user.json:

{
    "age": 26,
    "birth_day": 14,
    "birth_month": 6,
    "birth_year": 1993,
    "citizenship": "RU",
    "emails": ["alex@gmail.com", "alex@mail.ru"],
    "name": "Alexey",
    "occupations": [
        {
            "address": "Moscow",
            "employees": 8854,
            "title": "yandex"
        },
        {
            "address": "Yekaterinburg",
            "employees": 7742,
            "title": "skbkontur"
        }
    ],
    "passport_number": "836815",
    "passport_series": "3127",
    "phone": "+79204563539",
    "surname": "Ivanov"
}

Project details


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