2.0.0 • Published 11 months ago

@blending_jake/jtools v2.0.0

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11 months ago


JTools is a robust library for interacting with JSON-like objects: providing the ability to quickly query, format, and filter JSON-like data.

JTools is available in Python and JavaScript and consists of three main components:

  • Query: Extract and transform the values of nested fields.
    • Query("data.timestamp.$parse_timestamp.$time_part('year')").many(items)
  • Filter: Combine the querying capabilities of Query with the ability to define filtering conditions to find just the elements you want.
    • Filter(Key("data.timestamp.$parse_timestamp.$time_part('year')").gt(2015)).many(data)
  • Formatter: Take multiple queries and format them into a string
    • Formatter("Item @data.id was released in @data.timestamp.$parse_timestamp.$time_part('year')").single(data[0])

JTools exists in two different langauges with almost identical names and capabilities to allow you to move between the packages seamlessly.

Python - jtools

JavaScript - @blending_jake/jtools

Written in TypeScript and distributed as an ES6 style module with type declaration files.


  • In JTools-Py, the == and === filter operators will behave the same, as well as != and !==.
  • JTools-Py uses the datetime package for time related queries, while JavaScript uses moment
  • JTools-Py replicates JavaScript's lack of differentiation between item[0] and item["0"] by default. However, this can be changed in the Python version by setting Query(..., convert_ints=False). If that argument is set to False in Python, then item.0 would work on {"item": {"0": ...}}, but not on {"item": {0: ...}}. The JavaScript version essentially always has convert_ints=True.

Recent Changes

  • 2.0.0
    • Numerous new language features
      • Support for arithmetic in arguments. The supported operators are -, +, *, /, // (floor division), ** (exponentiation), and %. The operators can be used any place a value is valid within an argument, such as $special(14000 * 2), $special(@value // 2), $special([1, 1+1, 1+2]). The order of operations follows typical precedence, and arithmetic can be nested in ().
      • Support for keyword arguments:$index("value", fallback=12)
      • Whitespace is allowed in a lot more places in a query now, which is very helpful since both JavaScript and Python support multi-line strings.
    • Performance increase for cases were a Query field doesn't have any specials. A faster parsing method can be used for about a 40x performance increase in creating the Query object. Note, this just speeds up Query creation and not the speed of .single(), .many(), etc.
    • Added functionality so that Filter values can be queries.
      • Using JSON: { field: <field>, operator: <op>, value: { query: <value query> } }
      • Using Key: Key(<field>).<op>(Key(<value_query>))
      • For example: Key("tag.tag1").gt(Key("tag.tag2"))
    • Four new filters: subset, !subset, superset, !superset. These should be read field value <op> filter value, so subset means all of the values returned from the field query are in the filter value, which allows better filtering when both the field query and value are iterable.
    • Many new specials
      • $key_of_min_value - Gets the key of the min value in an dict/map/object
      • $key_of_max_value - Gets the key of the max value in an dict/map/object
      • $time_part(part) -> int - Get a specific part of a datetime/moment object. Valid values for part are as follows:
        • 'millisecond'
        • 'second'
        • 'minute' - Starting from 0
        • 'hour' - Starting from 0
        • 'day' - Day of month, starting from 1
        • 'month' - Month of year, starting from 1
        • 'year'
        • 'dayOfWeek' - Value in 0-6, corresponding to Monday-Sunday
        • 'dayOfYear' - Day of year, starting from 1
      • $min and $max
      • $arith(op, arg_value) - Perform an arithmetic operation on the current value. op can be any of the support math operators.
      • $lowercase, $uppercase, and $titlecase
      • $filter(field, op, value, single=true) OR $filter({<filter>}, single=true) OR $filter([<filters>], single=true) - Allow a single value or list of values to be filtered. The filters should be formatted that same way they are for Filter.
      • $pipeline(pipeline) - Apply multiple specials to value in a given order. Can be very useful when used in conjunction with $map to apply multiple specials at once. pipeline must be of format:


    [<special>, arg1, arg2, ..., (optional) map/object/dict of keyword arguments],

for example

    ['index', 'balance'],
    ['range', 1],
    ['replace', {'old': ',', 'new': ''}],

is the same as
$index("balance").$range(1).$replace(old=",", new="").$float
  • Updates to old specials
    • $index(i, fallback=null, extended=false) - added extended argument to allow $index to support any valid JQL query for i if extended=true
  • Bug fixes

    • Fixed issue with filters not shortcutting properly
    • Fixed Python issue with $print
    • Fixed issues with $fallback with Filter and Formatter
    • Fixed issue causing an error when trying to use an integer value in $sort and $group_by




pip install jtools

# import
from jtools import Query, Filter, Key, Condition, Formatter


npm i @blending_jake/jtools

// import
import { Query, Filter, Key, Condition, Formatter } from "@blending_jake/jtools";


from jtools import Query
# sort by nested timestamp field by month
q = Query("meta.timestamp.$parse_timestamp.$time_part('month')")
data = [ ... ]
sorted_data = sorted(data, key=q.single)


JQL or the JSON Query Language is a custom built query language for JTools which supports powerful features like accessing nested fields, transforming values, and even using nested queries as arguments. The basic format of the language is:

(<field> | $<special>) (. (<field> | $<special>))*
EX: 'data', 'data.timestamp', 'data.$split', '$split.0'


A field is just a value that can be used as an index, like a string or integer key for a map/dict or an integer for an array. JavaScript has very loose type-checking between strings and integers, so either can essentially work in place of the other when indexing.

Fields can only contain the following characters: [-a-zA-Z0-9_]. However, fields with prohibited characters can still be indexed by using the $index special, so to index range[0] use $index("range[0]").


A special is a function that is applied to the value that has been queried so far. There is a complete list of specials here. These specials can be passed arguments, which is one of the most powerful features of JQL.


Arguments can be passed into specials as a positional or keyword arguments. Positional arguments must come first and are denoted using the standard notation in most programming languages: $special(arg1, arg2, ...). Keyword arguments must come after any positional arguments and can be used to specify a specific argument to set the value for: $special(arg1, name1=arg2, name2=arg3, ...). Keyword arguments can be used to make it clear what argument you are setting - improving readability, or can be used to skip arguments which have default values.

For example, the index special has the following definition: $index(key, fallback=null, extended=false). If you want to use a JQL query for key, then you need to set extended=true. You can either write $index(key, null, true), or you can skip the fallback argument and write $index(key, extended=true). Using keyword arguments might not save many characters if the the special has few arguments, but can still greatly improve readability.

It is important to note that arguments, and the parenthesis surrounding them can be left completely off of a special if the default argument values are acceptable or there are no arguments - so a query like data.$values.$max.$divide(@data.$values.$sum) can be written where most of the parenthesis and arguments are just left off.


Arguments are considered values and must be one of the following types.

Math Expression
[] or [<value>(, <value>)*] - List
{} or {<value>(, <value>)*} - Set
{:} or {<key>: <value>(, <key>: <value>)*} - Map/Dict/Object (see below for <key> spec)
String w/ '' or ""
@<query> - Yep! Nested queries!

Math Expression:
    Operators listed below
    Operands must be one of: Integer, Float, or @<query>

    Math Expression

As shown above, values and queries can be nested, so [[1, 2], ["bob"], {"Ann", 'Ralph'}, {'key': 4, 23: 5}] is valid. Additionally, the support for nesting queries is extremely powerful and allows for queries like: item.tag.$lookup(@table.colors), which, for {"item": {"tag": "product"}, "table": {"colors": {"product": "red"}}} results in "red"

Basic math expressions are supported in arguments and, subsequently, nested values. The supported operators are listed below and follow normal arithmetic precedence with the order of evaluation from first -> last being: (), **, * and / and // and %, + and -.

The operands for math expressions are limited to numbers (Float and Integer) and nested queries.

Math expressions can be nested in other values, for example: $special([ 1, @value, @value**2, @value**3 ])

Math Operators
  • +
  • -
  • *
  • /
  • // - Floor division, aka Math.floor(a / b)
  • % - Mod operator
  • ** - Exponentiation, aka Math.pow(a, b) or a^b
  • () - Parenthesis can be use to change precedence and/or improve readability


Query takes the power of JQL and puts it into practice querying and transforming values in JSON-like data.

Query(query, fallback=null, [convert_ints=true (if Python)])

  • query: str | List[str] The field or fields to query
  • fallback: The value that will result if a non-existent field is queried
  • convert_ints: Whether or not to convert any digit-only fields to integers

.single(item, context={})

  • item: The item to query
  • context: See Context for more details

Take a single item and query it using the query(ies) provided

Query(field).single(...) -> result

Query([field, field, ...]).single(...) -> [result, result, ...]

.many(items, context={})

  • items: The items to query
  • context: See Context for more details

Take a list of items, and query each item using the query(ies) provided

Query(field).many(...) -> [result, result, ...]

Query([field, field, ...]).many(...) -> [[result, result, ...], [result, result, ...], ...]


  • More specials can be added by using the class method .register_special() like so: Query.register_special(<name>, <func>, <argDef> [if JavaScript]). The function should be formatted as such:
    # Python
    lambda value, *args, context: ...
    // JavaScript
    (value, context, args) => { ... }
    Where value is the current query value, and context is the current context.

Registering a special in JavaScript

Registering a special works differently in JavaScript because the language does not support keyword arguments. To get around this, an argument definition should be provided whenever the special is registered. The argument definition should be formatted:

    '<argument name>' | { 'name': '<argument name>', [ 'default': <default value> ] }

The argument definition allows you to state what the name of each parameter is, and allows a default value to be provided. Additionally, '$args' and '$kwargs' can be placed in the argument definition to capture a variable number of positional arguments or keyword arguments, respectively.

Each registered special function is then passed an object, args, which is { <argument name>: <argument value>, ... }. The keys '$args' and '$kwargs' capture the variable number of positional and keyword arguments, respectively.

Some example argument definitions and usages:

Query.register_special('index', (value, context, args) => {
    // use args.key, args.fallback, and args.extended to access arguments
}, [ 'key', { name: 'fallback', default: null }, { name: 'extended', default: false } ])

Query.register_special('filter', (value, context, args) => {
    // args.$args is an array of any positional arguments
    // args.single must be specified as a keyword argument (as it's after $args)
}, [ '$args', { name: 'single', default: false } ])

Query.register_special('update', (value, context, args) => {
    // args.$kwargs is an object of any captured key->value pairs
    return { ...value, ...args.$kwargs };
}, [ '$kwargs' ])


Context is a way of putting temporary variables into the query search space.

How do I add something to context?
  1. Manually introduce values through .single(..., context) or .many(..., context).
  2. Use the $store_as() special to place a value in the current context for later use
How do I access something in context?
  1. Any top-level field name is first looked for on the current item, then in context. Note, top-level means it is the main query in a Query string, or it follows an @, either as an argument or in a Formatter string.
  2. It is important to note that fields on the current item will shadow fields in the context, so make sure to use unique field names.
Ok, but give me an example.
# Python
context = {
  "NOW": time.time()

Query("NOW.$subtract(@meta.timestamp).$divide(86400).$round.$suffix(' Days Ago')").single({ ... }, context)
// JavaScript
const context = {
  NOW: Date.now() / 1000

new Query("NOW.$subtract(@meta.timestamp).$divide(86400).$round.$suffix(' Days Ago')").single({ ... }, context)



  • $inject(value: any) -> any: Inject a value into the query
  • $length -> int
  • $lookup(lookup: dict, fallback=null) -> any: Lookup the current value in the provided map/dict
  • $store_as(name: string) -> any: Store the current query value in the current context for later use in the query. This does not change the underlying data being queried.
  • $pipeline(pipeline) -> any: Take a value and run it through multiple specials. Can be used in conjunction with $map or $value_map to apply a series of transformations across a list of values. pipeline must be a list where each value is:
    • string - Name of special
    • [string, *args] - Name + positional arguments
    • [string, dict of keyword args] - Name + dict/map/object of keyword arguments
    • [string, *args, dict of keyword args] - Name + positional arguments + dict/map/object of keyword arguments
# Python
        ['divide', 1000],
        ['time_part', 'year']
  • $print -> any: Print the current query value before continuing to pass that value along
  • $filter(field, op, value, single=true) OR $filter({<filter>}, single=true) OR $filter([<filters>], single=true): Allow a single value or list of values to be filtered. The filters should be formatted that same way they are for Filter. single can only be supplied as a keyword argument.


  • $items -> List[[any, any]]
  • $keys -> List[any]
  • $key_of_max_value(just_key=true) -> any | [any, any]: Find the key of the max value in a dict/object/map. If just_key=true, then just the value of the key will be returned. Otherwise, the [key, value] will be returned.
  • $key_of_min_value(just_key=true) -> any | [any, any]: Find the key of the min value in a dict/object/map. If just_key=true, then just the value of the key will be returned. Otherwise, the [key, value] will be returned.
  • $wildcard(nxt, just_field=true) -> List[any]: On a given map or list, go through all values and see if nxt is a defined field. If it is, then return just the value of nxt on that item, if just_field=true, or the entire item otherwise. This special allows a nested field to be extracted across multiple items where it it present. For example:
# Python
data = {
  "a": {"tag": "run"},
  "b": {"tag": "to-do", "other": "task"},
  "meta": None
Query('$wildcard("tag")').single(data)  # => ["run", "to-do"]
Query('$wildcard("tag", false)').single(data) # => [{"tag": "run"}, {"tag": "to-do", "other": "task"}]
// JavaScript
let data = {
  "a": {"tag": "run"},
  "b": {"tag": "to-do", "other": "task"},
  "meta": null
new Query('$wildcard("tag")').single(data)  // => ["run", "to-do"]
new Query('$wildcard("tag", false)').single(data) // => [{"tag": "run"}, {"tag": "to-do", "other": "task"}]
  • $values -> List[any]
  • $value_map(special, duplicate=true, *args, **kwargs): Dict[any: any]: Go through the values on the current item in the query, applying a special to each one in-place. If duplicate=true, then the original value will not be modified. Similar to:


for key in value: valuekey = SPECIALSspecial(valuekey, *args, **kwargs)

// JavaScript
Object.keys(value).forEach(key => {
   value[key] = SPECIALS[special](value[key], ...args, ...kwargs);

Type Conversions

  • $dict -> Dict[any: any]: Take an incoming list of (key, value) pairs and make a map/dict/object out of them.
  • $fallback(fallback) -> value or fallback: If the value is null, then it will be replaced with fallback.
  • $float -> float
  • $int -> int
  • $not -> bool: Returns not value or !value
  • $set -> set
  • $string -> str
  • $ternary(if_true, if_false, strict=false) -> any: Return if_true if the value is truish, otherwise, return if_false. Pass true for strict if the value must be true and not just truish.


  • $parse_timestamp -> datetime or moment: Take a Unix timestamp in seconds and return a corresponding datetime/moment object
  • $strftime(fmt="%Y-%m-%dT%H:%M:%SZ" or "YYYY-MM-DD[T]HH:mm:ss[Z]") -> string: Format a datetime/moment object as a string using fmt. Refer to datetime or moment for formatting instructions
  • $strptime(fmt=null) -> datetime or moment: Parse a datetime string and return a corresponding datetime/moment object. If fmt=None, then standard formats will be tried. Refer to datetime or moment for formatting instructions
  • $timestamp -> int: Dump a datetime/moment object to a UTC timestamp as the number of seconds since the Unix Epoch
  • $time_part(part) -> int: Take a datetime or moment value and get a specific part of the date. part can be:

    • millisecond
    • second
    • minute
    • hour
    • day
    • month
    • year
    • dayOfWeek
    • dayOfYear

Math / Numbers

  • $abs(num) -> number
  • $add(num) -> number
  • $arith(op, arg_value) -> number: Take the value and use it as the first operand of an expression with the specified math operator. op can be any of the math operators. The expression will be value op arg_value.
  • $distance(other) -> float: Euler distance in N-dimensions
  • $divide(num) -> number
  • $math(attr, ...args) -> any: Returns math[attr](value, ...args), which can be used for operations like floor, cos, sin, min, etc. See the Python Docs for valid attr values in Python and the JavaScript Docs for valid attr values in JavaScript.
  • $multiply(num) -> number
  • $pow(num) -> number
  • $round(n=2) -> number
  • $subtract(num) -> number


  • $lowercase -> string
  • $prefix(prefix) -> string: Prefix the value with the specified string
  • $replace(old, new) -> string: Replace all occurrences of a string
  • $split(on=" ") -> List[string]: Split a string
  • $strip -> string: Strip leading and trailing whitespace
  • $suffix(suffix) -> string: Concatenate a string to the end of the value
  • $titlecase -> string
  • $trim(length=50, suffix="...") -> string: Trim the length of a string
  • $wrap(prefix, suffix) -> string: Wrap a string with a prefix and suffix. Combines features of above two specials.
  • $uppercase -> string


  • $group_by(key="", count=false) -> Dict[any: any[] | int]: Take an incoming list and group the values by the specified key. Any valid JQL query or integer can be used for the key. "" means the value itself. The result by default will be keys to a list of values. However, if count=true, then the result will be keys to the number of elements in that group.
  • $index(key, fallback=null, extended=false) -> any: Index the current piece of data either using a string or index key, or a full JQL query if extended=true. If the index is invalid, then fallback will be returned. If extended=false and key is an integer, then a negative key can be used to index from the end of the array.
  • $join(sep=", ") -> string: Join a list using the specified separator
  • $join_arg(arg: List[any], sep=", "): Similar to $join except this operates on an argument instead of the query value. Essentially a shortened form of $inject(arg).$join(sep).
  • $map(special, *args, **kwargs) -> List[any]: Apply special to every element in the value. Arguments can be passed through to the special being used.
  • $max -> number: Find the max value in the list
  • $min -> number: Find the min value in the list
  • $sum -> number: Return the sum of the items in the value
  • $range(start, end=null) -> List[any]: Get a sublist. Defaults to value.slice(start) or value[start:], but an end value can be specified. Negative indices are allowed.
  • $remove_nulls -> List[any]: Remove any values that are None if Python, or null and undefined if JavaScript
  • $sort(key="", reverse=false) -> List[any]: Sort an incoming list of values by a given key which can be any valid JQL query or an integer. By default, key="" means the top-level value will be sorted on.Attributes
  • $attr(attr) -> any: Access an attribute of the given object, implemented as getattr(value, attr) and value[attr]
  • $call(func, *args, **kwargs) -> any: Call a function that is on the current value, implemented as getattr(value, func)(*args) and value[func](...args)


Filter takes the power of JQL and combines it with filtering conditions to allow lists of items to be filtered down to just those of interest. The filters can be manually built, or the Key and Condition classes can be used to simplify your code.

new Filter(filters, [convert_ints=true (if Python)], empty_filters_response=true, missing_field_response=false)

  • filters: Condition | List[dict] The filters to apply to any data. If List[dict], then the filters should be formatted as shown below.
    {"field": <field>, "operator": <op>, "value": <value>},


    {"or": <nested outer structure>},

    {"not": <nested outer structure>},

<field>: any valid `JQL` query
<op>: See list below
<value>: Any valid value for the operator, or 
    { "query": <JQL query> } to have a value which is a query
  • convert_ints: bool Corresponds with the argument with the same name in Query. Determines whether digit only fields are treated as integers or strings. Defaults to true.
  • empty_filters_response: bool Determines what gets returned when no filters are supplied.
  • missing_field_response: bool Determines the result of a filter where the field could not be found.

Filters are evaluated in order and short-cutting can be used to avoid executing filters. For example, a present operator can be used before trying to access or manipulate a field. Additionally, the $fallback special can be used to the same effect in certain cases.

.single(item, context={})

  • context: See Context for more details

    Take a single item and determine whether it satisfies the filters or not

    Filter(filters).single(...) -> boolean

.many(items, context={})

  • context: See Context for more details

    Take a list of items, and returns only those which satisfy the filters. Note, Filter.many() introduces INDEX into the query namespace. Allowing items to be filtered by their 0-based index.

    Filter(filters).many(...) -> [result, result, ...]


{"or": [ 
    [ {filter1}, {filter2} ], 
]} === (filter1 AND filter2) OR filter3

Nesting in an or will cause those filters to be AND'd and then everything in the toplevel of that or will be OR'd.


  • >
  • <
  • >=
  • <=
  • ==
  • !=
  • ===
  • !==
  • in: <field> in <value>
  • !in
  • contains: <value> in <field>
  • !contains
  • subset: x in <value> for x in <field>
  • !subset: exists x in <field> such that x not in <value>
  • superset: x in <field> for x in <value>
  • !superser: exists x in <value> such that x not in <field>
  • interval: <field> in interval [value[0], value[1]] (closed/inclusive interval)
  • !interval: <field> not in interval [value[0], value[1]]
  • startswith
  • endswith
  • present
  • !present


Intended to simplify having to write {"field": <field>, "operator": <operator>, "value": value} a lot. The basic usage is: Key(<field>).<op>(<value>), or for the first six operators, the actual Python operators can be used, so Key(<field>) <op> <value>. For example: Key("meta.id").eq(12) is the same as Key("meta.id") == 12, which is the same as {"field": "meta.id", "operator": "==", "value": 12}.

To use a filter where the value is a query itself, use Key(<field>) as the value. For example: Key("tags.tag1").gt(Key("tag.tag2")).

The table below describes all of the functions which map to the underlying conditions. Additionally, several other methods are provided to simplify certain aspects of building filters and conditions:

  • Key(field).is_true(): Same as Key(field).seq(true)
  • Key(field).is_false(): Same as Key(field).seq(false)
  • Key(field).is_null(): Same as Key(field).seq(null)
  • Key(field).op(operator).value(value): Same as Key(field).<op>(value). Can be used for times when you want to construct a filter and the operator is dynamic.


underlying operatorKey functionPython operator


Intended to be used in combination with Key to make creating filters easier than manually creating the JSON. There are three conditions supported: and, or, and not. They can be manually accessed via and_(...conditions), or_(...conditions), and not_().

The conditions can also be accessed through the overloaded operators &, |, and ~, respectively, if in Python. Caution: & and | bind tighter than the comparisons operators and ~ binds the tightest

Key("first_name") == "John" | Key("first_name") == "Bill" is actually (Key("first_name") == ("John" | Key("first_name"))) == "Bill", not (Key("first_name") == "John") | (Key("first_name") == "Bill")

Condition.ander(cond1, cond2, *conditions)

AND two or more conditions together

Condition.orer(cond1, cond2, *conditions)

OR two or more conditions together


AND the current condition with multiple other conditions


OR the current condition with multiple other conditions


NOT the current condition


Clone the current condition. If deep, then all aspects will be duplicated.

.traverse(callback, on_duplicate=false) -> Condition

Traverse through all of the filters in the current condition, calling callback(filter) with each one. on_duplicate indicates whether the current condition is iterated over, or a duplicate. Whatever condition was iterated over will be returned.

.to_list() -> list

Return a list of filters/conditions for this condition

Condition.from_list(conditions) -> Condition

Take a list of filters/conditions and make a Condition object out of it


# Python
Key("state").eq("Texas") | Key("city").eq("New York")

(Key("gender") == "male") & (Key("age") >= 18) & (Key("selective_service") == False)

    Key("product_id") == 15
# (year < 2005 OR year > 2015) AND product_id == 15
// JavaScript


Formatter allows fields to be queried from an object and then formatted into a string. Any queries in a format string should be prefixed with @ and any valid JQL query can be used. For example, new Formatter('Name: @name}').single({"name": "John Smith"}) results in Name: John Smith.

Formatter(spec, fallback="<missing>", [convert_ints=true (if Python)])

  • spec: str The format string
  • fallback: str The value that will be used in the formatted string if a query could not be performed. For example, if the field missing does exist, then the query "Age: @missing" will result in "Age: <missing>"
  • convert_ints: bool Whether digit-only fields get treated as integers or strings

.single(item, context={})

  • context: See Context for more details

    Return a formatted string or the fallback value if the query fails

.many(items, context={})

  • context: See Context for more details

    Return a list of formatted strings or the fallback value.


The differences between Query and Formatter are:

  • Query can return a value of any type, Formatter just returns strings
  • Formatter supports multiple queries, end-to-end, Query does not
  • All queries must be prefixed with @ with Formatter, not just when used as an argument like with Query
  • Both support all the features of JQL
  • Query actually can theoretically do everything Formatter does by using $prefix, $suffix, and $string. For example, '@name @age' -> 'name.$suffix(" ").$suffix(@age)'. However, the latter is much longer than the former

Example (flattening operations):

# Python
errors = {
    "errors": {
        "Process Error": "Could not communicate with the subprocess",
        "Connection Error": "Could not connect with the database instance"

Formatter('Errors: \n@errors.$items.$map("join", ": \\n\\t").$join("\\n")').single(errors)
# Errors:
# Process Error: 
#   Could not communicate with the subprocess
# Connection Error: 
#   Could not connect with the database instance
// JavaScript
const errors = {
    errors: {
        "Process Error": "Could not communicate with the subprocess",
        "Connection Error": "Could not connect with the database instance"

new Formatter('Erros: @errors.$items.$map("join", ": \\n\\t").$join("\\n")}').single(errors);
// Errors: 
// Process Error: 
//   Could not communicate with the subprocess
// Connection Error: 
//   Could not connect with the database instance

The above example shows a powerful usage of flattening errors into its items, then joining each item; splitting the error name and message between lines, then joining all the errors together.

Example (nested replacement):

# Python
item = {
    "x1": 1,
    "y1": 1,
    "x2": 12,
    "y2": 54

    "Midpoint: [@x2.$subtract(@x1).$divide(2), @y2.$subtract(@y1).$divide(2)]"
# Midpoint: [5.5, 26.5]
// JavaScript
const item = {
    x1: 1,
    y1: 1,
    x2: 12,
    y2: 54

new Formatter(
    "Midpoint: [@x2.$subtract(@x1).$divide(2), @y2.$subtract(@y1).$divide(2)]"
// Midpoint: [5.5, 26.5]


There are several ways to increase the performance of querying, filtering, and formatting. The performance gains can be had by limiting the amount of times a query string has to be parsed. This means that using a Query, Filter, or Formatter object multiple times will be faster then creating a new object every time.


# Python
# slower
for item in items:
    f = Query("timestamp.$parse_timestamp").single(item)
    # do other stuff

# faster
query = Query("timestamp.$parse_timestamp")
for item in items:
    f = query.single(item)
    # do other stuff
// JavaScript
// slower
items.forEach(item => {
  let f = new Query("timestamp.$parse_timestamp").single(item);
  // do other stuff

// faster
const query = new Query("timestamp.$parse_timestamp");
items.forEach(item => {
  let f = query.single(item);
  // do other stuff

Across 10,000 runs:

  • Python
    • reusing Query can improve performance by 302x
    • reusing Filter can improve performance by 132x
    • reusing Formatter can improve performance by 377x.
  • JavaScript
    • reusing Query can improve performance by 192
    • reusing Filter can improve performance by 120x
    • reusing Formatter can improve performance by 210x.


  • 1.1.5

    • Unify README between Python and JavaScript versions
    • Expand documentation
  • 1.1.4

    • Added $value_map, which allows the values on an map/dict/object to be modified with a special, either in-place or on a duplicate
    • Exposed context so additional fields can manually be put into the current query space. This was already being used by $store_as. context can be passed to any .single() or .many() call.
    • Additionally, Filter.many() is now placing INDEX into the query space to allow items to be filtered by their 0-based index
    • Exposed many of the internal TypeScript types
  • 1.1.3

    • Changed the behavior of new Query(""), from returning the fallback value, to returning the source data element itself. For example, new Query("").single(data) === data.
    • Added SpecialNotFoundError, which is raised when an invalid special is queried. Can be imported as import { SpecialNotFoundError } from "@blending_jake/jtools";
    • Added new specials
      • $store_as(name) Store the current query value in the current context for later use in the query. This does not change the underlying data being queried.
      • $group_by(key="", count=false) Take an incoming list and group the values by the specified key. Any valid JQL query can be used for the key, so "" means the value itself. The result by default will be keys to a list of values. However, if count=true, then the result will be keys to the number of elements with each key.
      • $sort(key="", reverse=false) Sort an incoming list of values by a given key which can be any valid JQL query. By default, key="" means the top-level value will be sorted on.
      • $dict Take an incoming list of (key, value) pairs and make a dict out of them.
      • $join_arg(arg, sep=', ') Similar to $join except this operates on an argument instead of the query value. Essentially a shortened form of $inject(arg).$join(sep).
    • Changed the underlying special function definition to now include the keyword argument context. This argument is implemented to only be accessed by name to avoid collision if the user provides too many arguments in their query. The purpose of the context is to support specials adding values temporarily to the data namespace of the query, like $store_as does.
  • 1.1.2

    • Version 1.1.1 was skipped to keep on track with JTools-Py
    • Catch and handle Extraneous Input Error
    • Change JQL so that field and special names must only contain [-a-zA-Z0-9_]. $index can be used to get fields with prohibited characters. The change was to support more formatting use-cases, like Age: @age, DOB: @dob, which previously would have failed because the , would have been considered part of the field name.
    • Change Formatter so that fallback is just a string that is substituted for invalid queries, instead of being the entire return value. Previously, "Age: @missing" would result in None, now it results in "Age: <missing>". This change allows for better debugging as it becomes clear exactly which queries are failing.
    • Add function docstrings
  • 1.1.0

    • Rename Getter to Query to more accurately describe what the class does
    • Migrate queries to use JQL
      • The migration opens the door to nested queries in Query, allowing queries, prefixed with @ to be used as arguments to specials, or even as values in the supported argument data structures
      • Special arguments are no longer parsed as JSON, allowing features like sets, query nesting, and support for single and double quoted strings.
      • Formatter no longer uses {{}} to surround queries. Instead, all queries must be prefixed with @, so "{{name}} {{age}}" -> "@name @age". @@ must be used to get a literal @ in a formatted string: "bob@@gmail.com" -> "bob@gmail.com"
      • Formatter got about a 2x performance boost
    • Added $wrap(prefix, suffix) to combine $prefix and $suffix
    • Added $remove_nulls
    • Added $lookup(map, fallback=None)
    • Added $wildcard(next, just_value=True), which allows level of nesting to be "skipped", such that a list of sub-values where next is present
    • Added a fallback argument to $index
    • Added $print to display the current value in the query
    • Added $inject to allow any valid argument value to be injected into the query to be accessed and transformed by subsequent fields and specials
  • 1.0.6

    • Migrate to TypeScript, so a declaration file is now included in the distribution
    • Add this README
    • Add === and !== filters for strict equality checking. The methods seq and sne have been added to Key to correspond with the new filters.
    • Rename null -> !present and !null -> present. Corresponding methods have been renamed to not_present and present. This filter will catch values that are null or undefined.
    • Make membership filters (in, contains, !in and !contains) work properly with strings, arrays, associative arrays, and sets.
    • Remove $datetime. See below for replacement.
    • Add $call and $attr for calling a function and accessing an attribute. Can be used to replace $datetime functionality.
    • Remove Formatter.format and add Formatter.single and Formatter.many to be consistent across other classes and support formatting arrays of items.
    • Add more tests to increase coverage and do basic performance testing

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