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https://github.com/tabatkins/kdlpy

Handwritten KDL parser in Python 3
https://github.com/tabatkins/kdlpy

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Handwritten KDL parser in Python 3

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# KDL-py



A handwritten Python 3.7+ implemenation of a parser

for the [KDL Document Language](https://kdl.dev),

fully compliant with KDL 1.0.0.



[KDL](https://kdl.dev) is, as the name suggests, a document language,

filling approximately the same niche as JSON/YAML/XML/etc

to be a simple but powerful language for config files.

It combines the best of several of these languages,

while avoiding their pitfalls:

more general than JSON and more powerful than XML,

while avoiding the verbosity of XML

or the explosive complexity of YAML.



kdl-py, in particular, is focused on *ease-of-use*,

supporting things like date/times, ip addresses, urls, uuids, regexes, and binary data

directly in your KDL document

(via powerful but simple tagged values),

and parsing them into native Python types automatically,

or doing the reverse and letting you build KDL document trees

with these values directly,

and automatically and safely serializing them into KDL text

for later parsing!



You can customize parsing and serialization further for your application very easily,

by providing node or value "converters"

to turn plain KDL values or nodes

into application-specific types,

and then turning them back into KDL text automatically

merely by adding a `.to_kdl()` method to your classes.



## Installing



```sh

pipx install kdl-py

```



When installed, a `kdlreformat` command-line program is also made available,

which can canonicalize a KDL document. See [below](#kdlreformat) for options.



## Using



The `kdl.parse(str, parseConfig|None)` function parses, you guessed it, a string of KDL into a KDL document object:



```py3

import kdl



>>> import kdl

>>> doc = kdl.parse('''

... node_name "arg" {

...     child_node foo=1 bar=true

... }

... ''')

>>>

>>> doc

Document(

    nodes=[

        Node(

            name='node',

            args=['arg'],

            nodes=[

                Node(

                    name='child',

                    props=OrderedDict([

                        ('foo', 1.0),

                        ('bar', True)

                    ])

                )

            ]

        )

    ]

)

```



You can also create a `kdl.Parser()` object and call its `.parse()` method; `Parser` objects can set up parsing and printing options that'll apply by default. See below for how to configure parsing options.



Either way, you'll get back a `kdl.Document` object, which is fully mutable. By default, untagged KDL values are represented with native Python objects.



```py3

>>> doc.nodes[0].nodes[0].props["foo"] = 2

>>>

>>> print(doc)

node_name "arg" {

        child_node foo=2 bar=true

}



```



Stringifying a `kdl.Document` object will produce a valid KDL document back. You can also call `doc.print(printConfig|None)` to customize the printing with a `PrintConfig` object, described below.  See below for how to configure printing options.



### Inserting Native Values



kdl-py allows a number of native Python objects to be used directly in KDL documents by default,

and allows you to customize your own objects for use.



kdl-py automatically recognizes and correctly serializes the following objects:



* `bool`: as untagged `true` or `false`

* `None`: as untagged `null`

* `int`, `float`: as untagged decimal number

* `str`: as untagged string

* `bytes`: as `(base64)`-tagged string

* `decimal.Decimal`: as `(decimal)`-tagged string

* `datetime`, `date`, and `time`: as `(date-time)`, `(date)`, or `(time)`-tagged strings

* `ipaddress.IPv4Address` and `ipaddress.IPv6Address`: as `(ipv4)` or `(ipv6)`-tagged strings

* `urllib.parse.ParseResult` (the result of calling `urllib.parse.urlparse()`): as `(url)`-tagged string

* `uuid.UUID`: as `(uuid)`-tagged string

* `re.Pattern` (the result of calling `re.compile()`): as `(regex)`-tagged raw string



All of the tags used above are reserved and predefined by the [KDL specification](https://github.com/kdl-org/kdl/blob/main/SPEC.md#reserved-type-annotations-for-numbers-without-decimals).



In addition, any value with a `.to_kdl()` method

can be used in a kdl-py document.

The method will be called when the document is stringified,

and must return one of the kdl-py types,

or any of the native types defined above.



(For *parsing* KDL into these native types,

or your own types,

see the `ParseConfig` section, below.)



## Customizing Parsing



Parsing can be controlled via a `kdl.ParseConfig` object,

which can be provided in three ways.

In order of importance:



1. Passing a `ParseConfig` object to `kdl.parse(str, ParseConfig|None)`

	or `parser.parse(str, ParseConfig|None)`

	(if you've constructed a `kdl.Parser`).

2. Creating a `kdl.Parser(parseConfig|None, printConfig|None)`,

	which automatically applies it to its `.parse()` method if not overriden.

3. Fiddling with the `kdl.parsing.defaults` object,

	which is used if nothing else provides a config.



A `ParseConfig` object has the following properties:



* `nativeUntaggedValues: bool = True`



	Controls whether the parser produces native Python objects (`str`, `int`, `float`, `bool`, `None`) when parsing untagged values (those without a `(foo)` prefix), or always produces kdl-py objects (such as `kdl.String`, `kdl.Decimal`, etc).



* `nativeTaggedValues: bool = True`



	Controls whether the parser produces native Python objects

	when parsing *tagged* values,

	for some of [KDL's predefined tags](https://github.com/kdl-org/kdl/blob/main/SPEC.md#reserved-type-annotations-for-numbers-without-decimals):



	* `i8`, `i16`, `i32`, `i64`, `u8`, `u16`, `u32`, `u64` on numbers:

		Checks that the value is in the specified range,

		then converts it to an `int`.

		(It will serialize back out as an ordinary untagged number.)

	* `f32`, `f64` on numbers:

		Converts it to a `float`.

		(It will serialize back out as an ordinary untagged number.)

	* `decimal64`, `decimal128` on numbers, and `decimal` on strings:

		Converts it to a `decimal.Decimal` object.

		(Always reserializes to a `(decimal)`-tagged string.)

	* `date-time`, `date`, `time` on strings:

		Converts to a `datetime`, `time`, or `date` object.

	* `ipv4`, `ipv6` on strings:

		Converts it to an `ipaddress.IPv4Address` or `ipaddress.IPv6Address` object.

	* `url` on strings:

		Converts it to a `urllib.parse.ParseResult` tuple.

	* `uuid` on strings:

		Converts it to a `uuid.UUID` object.

	* `regex` on strings:

		Converts it to a `re.Pattern` object.

		(It will serialize back out as a raw string.)

	* `base64` on strings:

		Converts it to a `bytes` object.



* `valueConverters: Dict[ValueKey, Callable] = {}`



	A dictionary of ValueKey->converter functions,

	letting you parse values

	(like `(date)"2021-01-01"`)

	into whatever types you'd like.



	Whenever the parser encounters a value,

	it will attempt to find an entry in this dict

	whose [`ValueKey`](#ValueKey) matches the value.

	If it succeeds,

	it will call the associated converter function with two arguments:

	the fully-constructed kdl-py object,

	and a `ParseFragment` object giving you access

	to the precise characters parsed from the document

	(for the value; the tag, if any, won't be included, as you can get it from the object itself).

	Whatever you return will be inserted into the document

	instead of the originally-parsed value.



	You can produce KDL values

	(such as parsing `(hex)"0x12.e5"` into a `kdl.Decimal`,

	since KDL doesn't support fractional hex values),

	or produce any other Python type.

	If you return a non-KDL type,

	you probably want to ensure it has a `.to_kdl()` method

	(or is one of the supported built-in types),

	so it can be serialized back into a KDL document.



	Note that only *one* conversion can happen to a given value.

	Your converters are checked

	in the dictionary's iteration order,

	then if none of them succeeded

	it will attempt to run the `nativeUntaggedValues` or `nativeTaggedValues` behaviors,

	if they're turned on.

	If a converter returns `NotImplemented`,

	it will continue looking for a matching converter.



* `nodeConverters: Dict[NodeKey, Callable] = {}`



	Similar to `valueConverters`,

	except it uses [`NodeKey`s](#NodeKey),

	and it converts `kdl.Node`s instead.



	There is no native conversion of nodes;

	if none of your converters successfully run,

	the node will be inserted as-is.



### ParseFragment



`kdl.ParseFragment` is passed to your custom converters,

specified in `kdl.ParseConfig.tags`,

giving you direct access to the input characters

before any additional processing was done on them.

This is useful, for example,

to handle numeric types

that might have lost precision in the normal parse.



It exposes a `.fragment` property,

containing the raw text of the value

(after the tag, if any).



It also exposes a `.error(str)` method,

which takes a custom error message

and returns a `kdl.ParseError`

with the `ParseFragment`'s location already built in,

ready for you to `raise`.

This should be used if your conversion fails for any reason,

so your errors look the same as native parse errors.



## Customizing Printing



Like parsing, printing a kdl-py `Document` back to a KDL string can be controlled by a `kdl.PrintConfig` object,

which can be provided in three ways.

In order of importance:



1. Passing a `PrintConfig` object to `doc.print(PrintConfig|None)`.

2. Setting `doc.printConfig` to a `PrintConfig`.

	(This is done automatically for any documents produced by a `Parser`,

	if you pass the `printConfig` option to the constructor.)

3. Fiddling with the `kdl.printing.defaults` object,

	which is used if nothing else provides a config.



A `PrintConfig` object has the following properties:



* `indent: str = "\t"`



	The string used for each indent level.

	Defaults to tabs,

	but can be set to a sequence of spaces if desired

	(or anything else).



* `semicolons: bool = False`



	Whether or not nodes are ended with semicolons.

	(The printer always ends nodes with a newline anyway,

	so this is purely a stylistic choice.)



* `printNullArgs: bool = True`



	When `False`, automatically skips over any "null"/`None` arguments.

	This will corrupt documents that use the "null" keyword intentionally,

	but can be useful if you'd prefer to use a `None` value

	as a signal that the argument has been removed.



* `printNullProps: bool = True`



	Identical to `printNullArgs`,

	but applies to properties rather than arguments.



* `respectStringType: bool = True`



	When `True`, the printer will output strings as the same type they were in the input,

	either raw (`r#"foo"#`) or normal (`"foo"`).

	When `False`, the printer always outputs normal strings.



	Note that this only has an effect on `kdl.String` and `kdl.RawString` objects;

	if the document contains Python `str` objects,

	they will always output as normal strings.



* `respectRadix: bool = True`



	Similar to `respectStringType`,

	when `True` the printer will output numbers as the radix they were in the input,

	like `0x1b` for hex numbers.

	When `False`, the printer always outputs decimal numbers.



	Again, this only has an effect on kdl-py objects;

	native Python numbers are printed as normal for Python.



* `exponent: str = "e"`



	What character to use for the exponent part of decimal numbers,

	when printed with scientific notation.

	Should only be set to "e" or "E".



	Like the previous options, this only has an effect on kdl-py objects;

	native Python numbers are printed as normal for Python.



## Full API Reference



* `kdl.parse(str, config: kdl.ParseConfig|None) -> kdl.Document`

* `kdl.Parser(parseConfig: kdl.ParseConfig|None, printConfig: kdl.PrintConfig|None)`

	* `parser.parse(str, config: kdl.ParseConfig|None) -> kdl.Document`

	* `parser.print(config: kdl.PrintConfig|None) -> str`

* `kdl.Document(nodes: list[kdl.Node]?, printConfig: kdl.PrintConfig|None)`

	* `doc.print(PrintConfig|None) -> str`

	* `doc[NodeKey] -> Node` returns the first child node matching the [`NodeKey`](#NodeKey). Raises a `KeyError` if nothing matches the `NodeKey`, similar to a `dict`.

	* `doc.get(NodeKey, default: T = None) -> kdl.Node | T` returns the first child node matching the [`NodeKey`](#NodeKey). Returns the default value if nothing matches.

	* `doc.getAll(NodeKey) -> Iterable[kdl.Node]` returns all child nodes matching the [`NodeKey`](#NodeKey)

* `kdl.Node(name: str, tag: str|None, args: list[Any]?, props: dict[str, Any]?, nodes: list[kdl.Node]?)`

	* `node[NodeKey] -> Node` returns the first child node matching the [`NodeKey`](#NodeKey). Raises a `KeyError` if nothing matches the `NodeKey`, similar to a `dict`.

	* `node.get(NodeKey, default: T = None) -> kdl.Node | T` returns the first child node matching the [`NodeKey`](#NodeKey). Returns the default value if nothing matches.

	* `node.getAll(NodeKey) -> Iterable[kdl.Node]` returns all child nodes matching the [`NodeKey`](#NodeKey)

	* `node.getProps(ValueKey) -> Iterable[tuple[str, Any]]` returns an iterator of `(name, value)` pairs for the properties whose value matches the [`ValueKey`](#ValueKey)

		(Note: for this purpose, non-KDL values, such as `int`, have no tag, and can only meaningfully be tested via a `TypeKey`.)

	* `node.getArgs(ValueKey) -> Iterable[Any]` returns an iterator of the arguments that match the [`ValueKey`](#ValueKey)

		(Same disclaimer as `.getProps()`.)

	* `node.matchesKey(NodeKey) -> bool` returns whether the node matches the [`NodeKey`](#NodeKey)



* `kdl.Value` ‡

	* `val.matchesKey(ValueKey) -> bool` returns whether the value matches the [`ValueKey`](#ValueKey)

* `kdl.Binary(value: int, tag: str|None)`

* `kdl.Octal(value: int, tag: str|None)`

* `kdl.Decimal(mantissa: int|float, exponent: int|None, tag: str|None)`

	* `dec.value`: readonly, `mantissa * (10**exponent)`

* `kdl.Hex(value: int, tag: str|None)`

* `kdl.Bool(value: bool, tag: str|None)`

* `kdl.Null(tag: str|None)`

	* `null.value`: readonly, always `None`

* `kdl.RawString(value: str, tag: str|None)`

* `kdl.String(value: str, tag: str|None)`

* `kdl.ExactValue(chars: str, tag: str|None)` †

* `kdl.Numberish`, `kdl.Stringish` ‡

* `kdl.ParseConfig(...)` see above for options

	* `kdl.parsing.defaults`: default `ParseConfig`

* `kdl.PrintConfig(...)` see above for options

	* `kdl.printing.defaults`: default `PrintConfig`

* `kdl.ParseError`: thrown for all parsing errors

	* `error.msg: str`: hopefully informative

	* `error.line: int`: 1-indexed

	* `error.col: int`: 1-indexed

* `kdl.ParseFragment`: passed to converter functions

	* `pf.fragment`: slice from the source string

	* `pf.error(msg: str)` returns a `kdl.ParseError` with error location set properly already

* `kdl.nodeMatchesKey(val: Any, key: kdl.NodeKey) -> bool`

* `kdl.valueMatchesKey(val: Any, key: kdl.ValueKey) -> bool`

* `kdl.tagMatchesKey(val: str|None, key: kdl.TagKey) -> bool`

* `kdl.nameMatchesKey(val: str|None, key: kdl.NameKey) -> bool`

* `kdl.typeMatchesKey(val: str|None, key: kdl.TypeKey) -> bool`

	* Functions implementing the tag/name/type matching

		used by the `node.matchesKey()` and `value.matchesKey()` methods,

		in case you want to use the same filtering yourself.



† Not produced by the parser.

Can be returned by a user's `.to_kdl()` method

if they want to produce a value *precisely* in a particular syntax,

in a way that the built-in kdl-py classes don't.



‡ Not produced by the parser.

These are abstract base classes to help in type testing:

`Value` matches all eight value classes,

`Numberish` matches all four numeric value classes,

and `Stringish` matches both string value classes.



A few type aliases also exist,

used by the module in a few places

and potentially useful for your code:



* `kdl.KDLAny`: a `Document`, `Node`, or any of the `Value` subtypes

* `kdl.KDLValue`: any of the `Value` subtypes

* `kdl.KDLishValue`: a `KDLValue` or one of the supported Python native types [see "Inserting Native Types"](#inserting-native-types)

* `kdl.ValueKey`, `kdl.NodeKey`, `kdl.TagKey`, `kdl.NameKey`, `kdl.TypeKey`:

	the types for [`ValueKey`s](#ValueKey) and [`NodeKey`s](#NodeKey)

	(and their individual pieces)



These aliases only exist when `typing.TYPE_CHECKING` is true,

so they're *only* useful for writing types;

they won't be visible at runtime.



### `NodeKey`



A few data structures and functions take a `NodeKey`

to match against a node,

based on its name and/or tag.



A `NodeKey` is either a `NameKey` or a `(TagKey, NameKey)` tuple,

matching against the node's name and/or tag.



`NameKey`s and `TagKey`s can be:



* `None`:

	When matched against a tag, only succeeds against a `None` tag

	(aka a tagless node like `foo`).

	When matched against a name, automatically succeeds,

	since nodes are guaranteed to have a name.

* `...`:

	Always succeeds.

	Use this when, say,

	you want to match against a particular tag, regardless of the nodename,

	like `("my-tag", ...)`.

* a `str`:

	Succeeds if the tag/name is that exact string.

* a `re.Pattern` (a regex, such as `re.compile(r".*foo")`:

	Succeeds if the regex matches the tag/name.

	Note that this uses `.match()` semantics,

	automatically anchoring against the start of the string;

	prepend your regex with `.*?` if you want it to match anywhere.

* a function, taking a `str | None` and returning a `bool`:

	Succeeds if the function,

	when called with the tag/name,

	returns True.



So, for example,

`doc.getAll("foo")` would return all nodes whose name is "foo",

regardless of tag.

`doc.getAll(("my-tag", ...))` would return all nodes whose tag is "my-tag",

regardless of the node name.

`doc.getAll(re.compile(r"-"))` would return all nodes whose name starts with "-".

Etc.



### `ValueKey`



Similarly to `NodeKey`, a few things take a `ValueKey`

to match against values,

based on its tag and/or type.



A `ValueKey` is either a `TagKey` or a `(TagKey, TypeKey)` tuple,

matching against the value's tag and/or type.



`TagKey` works identically to how it appears in [`NodeKey`](#NodeKey).

`TypeKey` is either `...`, which matches any type,

or the same sort of argument you'd pass as the second argument to `isinstance()`.



For example,

a `"foo"` key would match any values with the tag "foo", like `(foo)1` or `(foo)"bar"`.

A `(..., kdl.Numberish)` will match any value that's a "number" type: a Hex, Octal, Binary, or Decimal, regardless of its tag.

Etc.



## `kdlreformat`



The `kdlreformat` command-line program is installed by default

when you install this module from pypi.

It can also be run manually from the `kdlreformat.py` file

at the root of this repository

(or from the `kdl.cli.cli()` function)



```

usage: kdlreformat [-h] [--indent INDENT] [--semicolons] [--radix]

                   [--no-radix] [--raw-strings] [--no-raw-strings]

                   [--exponent EXPONENT]

                   [infile] [outfile]



KDL parser/printer, letting you easily reformat KDL files into a canonical

representation.



positional arguments:

  infile

  outfile



optional arguments:

  -h, --help           show this help message and exit

  --indent INDENT      How many spaces for each level of indent. -1 indicates

                       to indent with tabs.

  --semicolons         Whether to end nodes with semicolons or not.

  --radix              Output numeric values in the radix used by the input.

                       (0x1a outputs as 0x1a)

  --no-radix           Convert all numeric arguments to decimal. (0x1a outputs

                       as 26)

  --raw-strings        Output string values in the string type used by the

                       input.

  --no-raw-strings     Convert all string arguments into plain strings.

  --exponent EXPONENT  What character to use ('e' or 'E') for indicating

                       exponents on scinot numbers.

```