treepath 2.0.1

A python query language, similar to xpath and jsonpath, for extracting data from a json data structure.

The treepath Package.

The treepath package offers a declarative programming approach to extracting data from a json data structure. The expressions are a query language similar to jsonpath, and Xpath, but are written in native python syntax.

Note python 3.6 is supported in version earlier that 1.0.0.

Quick start

All of the treepath components should be imported as follows:

from treepath import path, pathd, wc, wildcard, set_, get, get_match, find, find_matches, has, has_all,
    has_any, has_not, MatchNotFoundError, Match, log_to, Document, attr, attr_typed, attr_iter_typed,
    attr_list_typed, JsonArgTypes

A treepath example that fetches the value 1 from data.

data = {
    "a": {
        "b": [
            {
                "c": 1
            },
            {
                "c": 2
            }]
    }
}
value = get(path.a.b[0].c, data)
assert value == 1

A treepath example that fetches the values 1 and 2 from data.

value = [value for value in find(path.a.b[wc].c, data)]
assert value == [1, 2]

Solar System Json Document

The examples shown in this README use the following json document. It describes our solar system. Click to expand.

solar_system = {...}

{
  "star": {
    "name": "Sun",
    "diameter": 1391016,
    "age": null,
    "planets": {
      "inner": [
        {
          "name": "Mercury",
          "Number of Moons": "0",
          "diameter": 4879,
          "has-moons": false
        },
        {
          "name": "Venus",
          "Number of Moons": "0",
          "diameter": 12104,
          "has-moons": false
        },
        {
          "name": "Earth",
          "Number of Moons": "1",
          "diameter": 12756,
          "has-moons": true
        },
        {
          "name": "Mars",
          "Number of Moons": "2",
          "diameter": 6792,
          "has-moons": true
        }
      ],
      "outer": [
        {
          "name": "Jupiter",
          "Number of Moons": "79",
          "diameter": 142984,
          "has-moons": true
        },
        {
          "name": "Saturn",
          "Number of Moons": "82",
          "diameter": 120536,
          "has-moons": true
        },
        {
          "name": "Uranus",
          "Number of Moons": "27",
          "diameter": 51118,
          "has-moons": true
        },
        {
          "name": "Neptune",
          "Number of Moons": "14",
          "diameter": 49528,
          "has-moons": true
        }
      ]
    }
  }
}

Quick comparison between Imperative and Declarative Solution.

The following problem is solved using a Imperative Solution and a Declarative Solution to try to illustrate the differences between the two approaches.

The problem is fetch the planet by name from the given solar system json document.

Imperative Solution

The first example uses flow control statements to define a Imperative Solution. This is a very common approach to solving problems.

def get_planet_by_name(name, the_solar_system):
    try:
        planets = the_solar_system['star']['planets']
        for arc in planets.values():
            for planet in arc:
                if name == planet.get('name', None):
                    return planet
    except KeyError:
        pass
    return None

actual = get_planet_by_name('Earth', solar_system)
expected = {'Number of Moons': '1', 'diameter': 12756, 'has-moons': True, 'name': 'Earth'}
assert actual == expected

Declarative Solution

The second example uses treepath to define a declarative solution. It solves the same problem without defining any flow control statements. This keeps the Cyclomatic and Cognitive Complexity low.

def get_planet_by_name(name: str, the_solar_system):
    return get(
        path.star.planets.wc[wc][has(path.name == name)],
        the_solar_system,
        default=None
    )

actual = get_planet_by_name('Earth', solar_system)
expected = {'Number of Moons': '1', 'diameter': 12756, 'has-moons': True, 'name': 'Earth'}
assert actual == expected

query examples.

Description	Xpath	jsonpath	treepath
Find planet earth.	/star/planets/inner[name='Earth']	$.star.planets.inner[?(@.name=='Earth')]	path.star.planets.inner[wc][has(path.name == 'Earth')]
List the names of all inner planets.	/star/planets/inner[*].name	$.star.planets.inner[*].name	path.star.planets.inner[wc].name
List the names of all planets.	/star/planets/*/name	$.star.planets.[*].name	path.star.planets.wc[wc].name
List the names of all celestial bodies	//name	$..name	path.rec.name
List all nodes in the tree Preorder	//*	$..	path.rec
Get the third rock from the sun	/star/planets/inner[3]	$.star.planets.inner[2]	path.star.planets.inner[2]
List first two inner planets	/star/planets.inner[position()<3]	$.star.planets.inner[:2]	path.star.planets.inner[0:2]
		$.star.planets.inner[0, 1]	path.star.planets.inner[0, 2]
List planets smaller than earth	/star/planets/inner[Equatorial_diameter < 1]	$.star.planets.inner[?(@.['Equatorial diameter'] < 1)]	path.star.planets.inner[wc][has(path["Equatorial diameter"] < 1)]
List celestial bodies that have planets.	//*[planets]/name	$..*[?(@.planets)].name	path.rec[has(path.planets)].name

Traversal Functions

get

The get function returns the first value the path leads to.

Get the star name from the solar_system

sun = get(path.star.name, solar_system)
assert sun == 'Sun'

When there is no match, MatchNotFoundError is thrown.

try:
    get(path.star.human_population, solar_system)
    assert False, "Not expecting humans on the sun"
except MatchNotFoundError:
    pass

Or if preferred, a default value can be given.

human_population = get(path.star.human_population, solar_system, default=0)
assert human_population == 0

In addition to a constant, the default value may also be a callable

def population():
    return 0

human_population = get(path.star.human_population, solar_system, default=population)
assert human_population == 0

The default value can be automatically injected in to json document

human_population = get(path.star.human_population, solar_system, default=1, store_default=True)
assert human_population == solar_system["star"]["human_population"]

The data source can be a json data structure or a Match object.

parent_match = get_match(path.star.planets.inner, solar_system)
name = get(path[2].name, parent_match)
assert name == "Earth"

set_

The set_ function modifies the json document.

Use the set_ function to modify the star name.

sun = get(path.star.name, solar_system)
assert sun == 'Sun'
set_(path.star.name, "RedSun", solar_system)
sun = get(path.star.name, solar_system)
assert sun == 'RedSun'
assert solar_system["star"]["name"] == 'RedSun'

Use the set_ to add planet9. This example creates multiple objects in one step.

name = get(path.star.planets.outer[4].name, solar_system, default=None)
assert name is None
planets_count = len(list(find(path.star.planets.wc[wc].name, solar_system)))
assert planets_count == 8

set_(path.star.planets.outer[4].name, 'planet9', solar_system, cascade=True)

name = get(path.star.planets.outer[4].name, solar_system, default=None)
assert name == 'planet9'
planets_count = len(list(find(path.star.planets.wc[wc].name, solar_system)))
assert planets_count == 9

find

The find function returns an Iterator that iterates to each value the path leads to. Each value is determine on its iteration.

Find all of the planet names.

inner_planets = [planet for planet in find(path.star.planets.inner[wc].name, solar_system)]
assert inner_planets == ['Mercury', 'Venus', 'Earth', 'Mars']

The data source can be a json data structure or a Match object.

parent_match = get_match(path.star.planets.inner, solar_system)
inner_planets = [planet for planet in find(path[wc].name, parent_match)]
assert inner_planets == ['Mercury', 'Venus', 'Earth', 'Mars']

get_match

The get_match function returns the first Match the path leads to.

Get the star name from the solar_system

match = get_match(path.star.name, solar_system)
assert match.data == 'Sun'

When there is no match, MatchNotFoundError is thrown.

try:
    get_match(path.star.human_population, solar_system)
    assert False, "Not expecting humans on the sun"
except MatchNotFoundError:
    pass

Or if preferred, None is returned if must_match is set to False.

match = get_match(path.star.human_population, solar_system, must_match=False)
assert match is None

The data source can be a json data structure or a Match object.

parent_match = get_match(path.star.planets.inner, solar_system)
earth_match = get_match(path[2].name, parent_match)
assert earth_match.path_as_str == "$.star.planets.inner[2].name"
assert earth_match.data == "Earth"

find_matches

The find_matches function returns an Iterator that iterates to each match the path leads to. Each match is determine on its iteration.

Find the path to each of the inner planets.

for match in find_matches(path.star.planets.inner[wc], solar_system):
    assert match.path_as_str in [
        '$.star.planets.inner[0]',
        '$.star.planets.inner[1]',
        '$.star.planets.inner[2]',
        '$.star.planets.inner[3]',
    ]

The data source can be a json data structure or a Match object.

parent_match = get_match(path.star.planets.inner, solar_system)
for match in find_matches(path[wc], parent_match):
    assert match.path_as_str in [
        '$.star.planets.inner[0]',
        '$.star.planets.inner[1]',
        '$.star.planets.inner[2]',
        '$.star.planets.inner[3]',
    ]

The Match Class

The Match class provides metadata about the match.

match = get_match(path.star.name, solar_system)

The explicit path to the match

explicit_path = match.path
assert explicit_path == path.star.name

The string representation of the match including the value: "path=value"

assert repr(match) == "$.star.name=Sun"
assert str(match) == "$.star.name=Sun"

The string representation of the match, but with just the path component.

assert match.path_as_str == "$.star.name"

A list containing each match in the path.

assert match.path_match_list == [match.parent.parent, match.parent, match]

The key that points to the match value. The data_name is a dictionary key if the parent is a dict or an index if the parent is a list.

assert match.data_name == "name" and match.parent.data[match.data_name] == match.data

The value the path matched.

assert match.data == "Sun"

The parent match.

assert match.parent.path_as_str == "$.star"

The match can modify the value

match.data = "Soleil"
assert repr(match) == "$.star.name=Soleil"
del match.data
assert repr(match) == "$.star.name=None"
match.data = "Sun"
assert repr(match) == "$.star.name=Sun"
match.pop()
assert repr(match) == "$.star.name=None"

Tracing Debugging

All of the functions: get, find, get_match and find_matchesm, support tracing. An option, when enabled, records the route the algorithm takes to determine a match.

This example logs the route the algorithm takes to find the inner planets. The print function is give to capture the logs, but any single argument function can be used.

inner_planets = [planet for planet in find(path.star.planets.inner[wc].name, solar_system, trace=log_to(print))]
assert inner_planets == ['Mercury', 'Venus', 'Earth', 'Mars']

The results

"""
at $.star got {'name': 'Sun', 'dia...
at $.star.planets got {'inner': [{'name': ...
at $.star.planets.inner got [{'name': 'Mercury',...
at $.star.planets.inner[*] got {'name': 'Mercury', ...
at $.star.planets.inner[0].name got 'Mercury'
at $.star.planets.inner[*] got {'name': 'Venus', 'N...
at $.star.planets.inner[1].name got 'Venus'
at $.star.planets.inner[*] got {'name': 'Earth', 'N...
at $.star.planets.inner[2].name got 'Earth'
at $.star.planets.inner[*] got {'name': 'Mars', 'Nu...
at $.star.planets.inner[3].name got 'Mars'
"""

Path

The root

The path point to root of the tree.

match = get_match(path, solar_system)

assert match.data == solar_system

In a filter path point to the current element.

match = get_match(path.star.name[has(path == 'Sun')], solar_system)

assert match.data == 'Sun'

Dictionaries

Keys

The dictionary keys are referenced as dynamic attributes on a path.

inner_from_attribute = get(path.star.planets.inner, solar_system)
inner_from_string_keys = get(path["star"]["planets"]["inner"], solar_system)

assert inner_from_attribute == inner_from_string_keys == solar_system["star"]["planets"]["inner"]

Keys With Special Characters

Dictionary keys that are not valid python syntax can be referenced as double quoted strings.

sun_equatorial_diameter = get(path.star.planets.inner[0]["Number of Moons"], solar_system)

assert sun_equatorial_diameter == solar_system["star"]["planets"]["inner"][0]["Number of Moons"]

Dictionaries that have alot of keys with a dash in the name can can use pathd instead. It will interpret path attributes with underscore as dashes.

mercury_has_moons = get(pathd.star.planets.inner[0].has_moons, solar_system)

assert mercury_has_moons == solar_system["star"]["planets"]["inner"][0]["has-moons"]

Wildcard as a Key.

The wildcard attribute specifies all sibling keys. It is useful for iterating over attributes.

star_children = [child for child in find(path.star.wildcard, solar_system)]
assert star_children == [solar_system["star"]["name"],
                         solar_system["star"]["diameter"],
                         solar_system["star"]["age"],
                         solar_system["star"]["planets"], ]

The wc is the short version of wildcard.

star_children = [child for child in find(path.star.wc, solar_system)]
assert star_children == [solar_system["star"]["name"],
                         solar_system["star"]["diameter"],
                         solar_system["star"]["age"],
                         solar_system["star"]["planets"], ]

Comma Delimited Keys

Multiple dictionary keys can be specified using a comma delimited list.

last_and_first = [planet for planet in find(path.star["diameter", "name"], solar_system)]
assert last_and_first == [1391016, "Sun"]

List

Indexes

List can be access using index.

earth = get(path.star.planets.inner[2], solar_system)
assert earth == solar_system["star"]["planets"]["inner"][2]

List the third inner and outer planet.

last_two = [planet for planet in find(path.star.wc.wc[2].name, solar_system)]
assert last_two == ['Earth', 'Uranus']

Slices

List can be access using slices.

List the first two planets.

first_two = [planet for planet in find(path.star.planets.outer[:2].name, solar_system)]
assert first_two == ["Jupiter", "Saturn"]

List the last two planets.

last_two = [planet for planet in find(path.star.planets.outer[-2:].name, solar_system)]
assert last_two == ["Uranus", "Neptune"]

List all outer planets in reverse.

last_two = [planet for planet in find(path.star.planets.outer[::-1].name, solar_system)]
assert last_two == ["Neptune", "Uranus", "Saturn", "Jupiter"]

List the last inner and outer planets.

last_two = [planet for planet in find(path.star.wc.wc[-1:].name, solar_system)]
assert last_two == ["Mars", "Neptune"]

Comma Delimited Indexes.

List indexes can be specified as a comma delimited list.

last_and_first = [planet for planet in find(path.star.planets.outer[3, 0].name, solar_system)]
assert last_and_first == ["Neptune", "Jupiter"]

Wildcard as an Index.

The wildcard word can be used as a list index. It is useful for iterating over attributes.

all_outer = [planet for planet in find(path.star.planets.outer[wildcard].name, solar_system)]
assert all_outer == ["Jupiter", "Saturn", "Uranus", "Neptune"]

The wc is the short version of wildcard.

all_outer = [planet for planet in find(path.star.planets.outer[wc].name, solar_system)]
assert all_outer == ["Jupiter", "Saturn", "Uranus", "Neptune"]

The dictionary wildcard is given as dot notation and cannot be used to iterator over a list. The list wildcard is given as an index and cannot be used to iterate over dictionary keys.

all_planets = [p for p in find(path.star.planets.wc[wc].name, solar_system)]
assert all_planets == ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

Recursion

The recursive word implies recursive search. It executes a preorder tree traversal. The search algorithm descends the tree hierarchy evaluating the path on each vertex until a match occurs. On each iteration it continues where it left off. This is an example that finds all the planets names.

all_planets = [p for p in find(path.star.planets.recursive.name, solar_system)]
assert all_planets == ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

The rec is the short version of recursive.

all_planets = [p for p in find(path.star.planets.rec.name, solar_system)]
assert all_planets == ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

Here is another example that finds all the celestial bodies names.

all_celestial_bodies = [p for p in find(path.rec.name, solar_system)]
assert all_celestial_bodies == ['Sun', 'Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus',
                                'Neptune']

Filters

Filters are use to add additional search criteria.

has filter

The has function is a filter that evaluates a branched off path relative to its parent path. This example finds all celestial bodies that have planets.

sun = get(path.rec[has(path.planets)].name, solar_system)
assert sun == "Sun"

This search finds all celestial bodies that have a has-moons attribute.

all_celestial_bodies_moon_attribute = [planet for planet in find(path.rec[has(pathd.has_moons)].name, solar_system)]
assert all_celestial_bodies_moon_attribute == ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus',
                                               'Neptune']

This search finds all celestial bodies that have moons. Note the operator.truth is used to exclude planets that don't have moons.

all_celestial_bodies_moon_attribute = [planet for planet in
                                       find(path.rec[has(pathd.has_moons, operator.truth)].name, solar_system)]
assert all_celestial_bodies_moon_attribute == ['Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

has filter comparison operators

Filters can be specified with a comparison operator.

earth = [planet for planet in find(path.rec[has(path.diameter == 12756)].name, solar_system)]
assert earth == ['Earth']

earth = [planet for planet in find(path.rec[has(path.diameter != 12756)].name, solar_system)]
assert earth == ['Sun', 'Mercury', 'Venus', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

earth = [planet for planet in find(path.rec[has(path.diameter > 12756)].name, solar_system)]
assert earth == ['Sun', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

earth = [planet for planet in find(path.rec[has(path.diameter >= 12756)].name, solar_system)]
assert earth == ['Sun', 'Earth', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

earth = [planet for planet in find(path.rec[has(path.diameter < 12756)].name, solar_system)]
assert earth == ['Mercury', 'Venus', 'Mars']

earth = [planet for planet in find(path.rec[has(path.diameter <= 12756)].name, solar_system)]
assert earth == ['Mercury', 'Venus', 'Earth', 'Mars']

has filter type conversion

Sometimes the value is the wrong type for the comparison operator. In this example the attribute "Number of Moons" is str type.

planets = [planet for planet in find(path.rec[has(path["Number of Moons"] > "5")].name, solar_system)]
assert planets == ['Jupiter', 'Saturn']

This is how to convert the type to an int before applying the comparison operator.

planets = [planet for planet in find(path.rec[has(path["Number of Moons"] > 5, int)].name, solar_system)]
assert planets == ['Jupiter', 'Saturn', 'Uranus', 'Neptune']

has filter comparison operators as single argument functions

A filter operator can be specified as a single argument function. Here an example that searches for planets that have the same diameter as earth.

earths_diameter = partial(operator.eq, 12756)
earth = [planet for planet in find(path.rec[has(path.diameter, earths_diameter)].name, solar_system)]
assert earth == ['Earth']

Any single argument function can be used as an operator. This example uses a Regular Expression to finds planets that end with s.

name_ends_with_s = re.compile(r"\w+s").match
earth = [planet for planet in find(path.rec[has(path.name, name_ends_with_s)].name, solar_system)]
assert earth == ['Venus', 'Mars', 'Uranus']

This example uses a closure to find planets that have the same diameter as earth.

def smaller_than_earth(value):
    return value < 12756

earth = [planet for planet in find(path.rec[has(path.diameter, smaller_than_earth)].name, solar_system)]
assert earth == ['Mercury', 'Venus', 'Mars']

logical and, or and not filters

has_all

A regular express to test if second letter in the value is an a.

second_letter_is_a = re.compile(r".a.*").fullmatch

The has_all function evaluates as the logical and operator. It is equivalent to: (arg1 and arg2 and ...)

found = [planet for planet in find(
    path.rec[has_all(path.diameter < 10000, (path.name, second_letter_is_a))].name,
    solar_system)
         ]
assert found == ['Mars']

has_any

The has_any function evaluates as the logical or operator. It is equivalent to: (arg1 and arg2 and ...)

found = [planet for planet in find(
    path.rec[has_any(path.diameter < 10000, (path.name, second_letter_is_a))].name,
    solar_system)
         ]
assert found == ['Mercury', 'Earth', 'Mars', 'Saturn']

has_not

The has_not function evaluates as the logical not operator. It is equivalent to: (not arg) This example find all the planets names not not equal to Earth. Note the double nots.

found = [planet for planet in find(
    path.rec[has_not(path.name != 'Earth')].name,
    solar_system)
         ]
assert found == ['Earth']

Combining has, has_all, has_any, and has_not filters.

Each of the has function can be passed as arguments to any of the other has function to construct complex boolean equation. This example is equivalent to: (10000 > diameter or diameter > 20000) and second_letter_is_a(name))

found = [planet for planet in find(
    path.rec[has_all(has_any(path.diameter < 10000, path.diameter > 20000), (path.name, second_letter_is_a))].name,
    solar_system)
         ]
assert found == ['Mars', 'Saturn']

has.these

The decorator has.these can be used to construct the boolean equations more explicitly. This example shows to use python built in and, or and not operators.

@has.these(path.diameter < 10000, path.diameter > 20000, (path.name, second_letter_is_a))
def predicate(parent_match: Match, small_diameter, large_diameter, name_second_letter_is_a):
    return (small_diameter(parent_match) or large_diameter(parent_match)) and name_second_letter_is_a(parent_match)

found = [planet for planet in find(path.rec[predicate].name, solar_system)]
assert found == ['Mars', 'Saturn']

A custom filter.

A predicate is a single argument function that returns anything. The argument is the current match. The has function is a fancy predicate.

This example writes a custom predicate that find all of Earth's neighbours.

def my_neighbor_is_earth(match: Match):
    i_am_planet = get_match(path.parent.parent.parent.planets, match, must_match=False)
    if not i_am_planet:
        return False

    index_before_planet = match.data_name - 1
    before_planet = get_match(path[index_before_planet][has(path.name == "Earth")], match.parent,
                              must_match=False)
    if before_planet:
        return True

    index_after_planet = match.data_name + 1
    before_planet = get_match(path[index_after_planet][has(path.name == "Earth")], match.parent,
                              must_match=False)
    if before_planet:
        return True

    return False

earth = [planet for planet in find(path.rec[my_neighbor_is_earth].name, solar_system)]
assert earth == ['Venus', 'Mars']

Class Descriptors

basic path descriptor

paths can be added as properties to a class using the path_descriptor function.

planets = path.star.planets.wc[wc]

class SolarSystem(Document):
    jupiter_name = attr(path.star.planets.outer[0].name)
    saturn_name = attr(path.star.planets.outer[1].name)
    big_planets = attr(planets[has(path.diameter > 25000)].name, getter=find)
    small_planets = attr(planets[has(path.diameter <= 25000)].name, getter=find, to_wrapped_value=list)
    number_of_planets = attr(planets, getter=find, to_wrapped_value=lambda itr: len(list(itr)))

The property support both gets and sets and dels

ss = SolarSystem(solar_system)
assert ss.jupiter_name == 'Jupiter'
assert ss.saturn_name == 'Saturn'

Rename Jupiter to Planet 5

ss.jupiter_name = 'Planet 5'
assert ss.jupiter_name == 'Planet 5'

The assignment operation alters the original document.

assert solar_system["star"]["planets"]["outer"][0]["name"] == 'Planet 5'

remove Jupiter's name

del ss.jupiter_name
with pytest.raises(MatchNotFoundError):
    print(ss.jupiter_name)
assert "name" not in solar_system["star"]["planets"]["outer"][0]

There are still 8 planets because only Jupiter's name was delete

assert ss.number_of_planets == 8

list all the big planets. Remember Jupiter was deleted.

big_planets = [name for name in ss.big_planets]
assert big_planets == ['Saturn', 'Uranus', 'Neptune']

list all the small planets.

assert ss.small_planets == ['Mercury', 'Venus', 'Earth', 'Mars']

document typed path descriptor

A descriptor support wrapping json types with an adaptor class. This example wraps the json that represents a planet with the planet class. The Planet class extends the Document class which provides the marshalling methods.

class Planet(Document):
    name = attr(path.name)

class SolarSystem(Document):
    jupiter = attr_typed(Planet, path.star.planets.outer[0])
    planets = attr_iter_typed(Planet, path.star.planets.wc[wc])
    outer_planets = attr_list_typed(Planet, path.star.planets.outer)

The getter returns the planet type

ss = SolarSystem(solar_system)
planet = ss.jupiter
assert planet.name == 'Jupiter'

rename Jupiter to Planet 5

planet.name = 'Planet 5'
assert planet.name == 'Planet 5'

The assignment operation alters the original document.

assert solar_system["star"]["planets"]["outer"][0]["name"] == 'Planet 5'

Jupiter can be renamed by replacing the planet with an imposter.

impostor_planet = Planet({})
impostor_planet.name = 'Imposter Jupiter'
ss.jupiter = impostor_planet
assert ss.jupiter.name == 'Imposter Jupiter'

The imposter planet also alters the original document.

assert solar_system["star"]["planets"]["outer"][0]["name"] == 'Imposter Jupiter'

An attribute descriptor can return an iterator where each element is converted to the correct type.

planets = [planet.name for planet in ss.planets]
assert planets == ['Mercury', 'Venus', 'Earth', 'Mars', 'Imposter Jupiter', 'Saturn', 'Uranus', 'Neptune']

An attribute descriptor can return an list where each element is converted to the correct type.

assert ss.outer_planets[0].name == 'Imposter Jupiter'

The list can be modified and the underline document is modified too.

jupiter = Planet({})
jupiter.name = 'Jupiter'
ss.outer_planets[0] = jupiter
planets = [planet.name for planet in ss.planets]
assert planets == ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']

custom typed path descriptor

A descriptor support wrapping json types with an adaptor class. This example wraps the json that represents a planet with the planet class. This Planet class defines its own marshalling methods.

class Planet:
    def __init__(self, name: str = None):
        self._name = name

    @property
    def name(self) -> str:
        return self._name

    @name.setter
    def name(self, name: str):
        self._name = name

    @staticmethod
    def to_wrapped_value(json_: JsonArgTypes) -> Planet:
        return Planet(json_["name"])

    @staticmethod
    def to_json_value(planet_: Planet) -> JsonArgTypes:
        return {"name": planet_.name}

class SolarSystem(Document):
    jupiter = attr_typed(Planet, path.star.planets.outer[0],
                         to_wrapped_value=Planet.to_wrapped_value,
                         to_json_value=Planet.to_json_value)
    planets = attr_iter_typed(Planet, path.star.planets.wc[wc],
                              to_wrapped_value=Planet.to_wrapped_value)
    outer_planets = attr_list_typed(Planet, path.star.planets.outer,
                                    to_wrapped_value=Planet.to_wrapped_value,
                                    to_json_value=Planet.to_json_value)

The getter returns the planet type

ss = SolarSystem(solar_system)
planet = ss.jupiter
assert planet.name == 'Jupiter'

rename Jupiter to Planet 5

planet.name = 'Planet 5'
assert planet.name == 'Planet 5'

Jupiter can be renamed by replacing the planet with an imposter.

impostor_planet = Planet()
impostor_planet.name = 'Imposter Jupiter'
ss.jupiter = impostor_planet
assert ss.jupiter.name == 'Imposter Jupiter'

The imposter planet also alters the original document.

assert solar_system["star"]["planets"]["outer"][0]["name"] == 'Imposter Jupiter'

An attribute descriptor can return an iterator where each element is converted to the correct type.

planets = [planet.name for planet in ss.planets]
assert planets == ['Mercury', 'Venus', 'Earth', 'Mars', 'Imposter Jupiter', 'Saturn', 'Uranus', 'Neptune']

An attribute descriptor can return an list where each element is converted to the correct type.

assert ss.outer_planets[0].name == 'Imposter Jupiter'

The list can be modified and the underline document is modified too.

jupiter = Planet()
jupiter.name = 'Jupiter'
ss.outer_planets[0] = jupiter
planets = [planet.name for planet in ss.planets]
assert planets == ['Mercury', 'Venus', 'Earth', 'Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune']