treepath 1.0.0rc7

A dev tool for performing queries on json objects.

The treepath Package

treepath uses declarative programming approach for 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.

Quick start

    from treepath import path, get
    data = {
        "a": {
            "b": {
                "c": 1
            }
        }
    }
    value = get(path.a.b.c, data)
    assert value == 1

Quick comparison between Imperative and Declarative Solution

To understand how treepath can differs from Imperative solution, here is an example problem showing both an Imperative and declarative solution.

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

The example solar system json document can be found [Here](# 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

Return a default value when match is not found.

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

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

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

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.

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

Return a None when match is not found.

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.

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

parent_match = get_match(path.star.planets.inner, solar_system)
for match in find_matches(path[wc], parent_match):
    assert match.path 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 string representation of match = [path=value].

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

A list containing each match in the path.

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

The string representation of match path.

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

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 == "$.star"

Tracing Debugging

All of the functions get, find, get_match and find_matches, support tracing. An option to record the route the algorithm took to determine a match. This is a useful option for debugging a path.

This example logs to the print method, the end to end route taken to find all of the planet names.

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 quoted as 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 dynamic attribute 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 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 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 to 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.

The 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 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 different from a list wildcard. One cannot be use to iterate over the other.

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 is a preorder tree traversal. The search algorithm descends the tree hierarchy evaluated the path on each vertex. It starts relative to its parent and stops on each match. 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 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 to exclude planest 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 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

Filters operator can be specified as a single argument function. Here an Earth example that searches for a 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 filter

A regex 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']

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']

The has_not function evaluates as the logical not operator. It is equivalent to: (not arg)

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

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']

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']

has.these filter

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

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 earths 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']

Solar System Json document

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

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
        }
      ]
    }
  }
}