Moment/docs/PCN.md

PCN File Format

This document explains in details the PCN (Python Config Notation) format. PCN files are organized in a hierarchy of sections and properties. PCN files can also contain normal Python code, such as imports and custom functions.

• Overview
• Sections
  • Including Built-in Files
  • Including User Files
  • Inheritance
• Properties
  • Common Types
  • Expressions
  • Section Access
  • Bracket Access
• GUI files

Overview

# Lines starting with a "#" are considered comments. 
# Comments can also be added to the end of normal lines.

# Sections can contain indented properties, other sections or functions.
class Example:
    # Properties are written as "name: type = value", examples:
    integer_number:   int       = 5
    decimal_number:   float     = 2.5
    character_string: str       = "Sample text"
    boolean:          bool      = True  # or False
    string_list:      List[str] = ["foo", "bar", "baz"]

    # Property values can be any Python expression, e.g. math operations:
    other_number: int  = (5 * 4) / 2

    # "self" points to the current section, Example, containing other_number.
    above_10: bool = self.other_number > 10  # result: False

    class Names:
        # Property names with characters outside of a-z A-Z 0-9 _ need quoting:
        "@alice:example.org": str = "Alice"
        "@bob:example.org":   str = "Bob"

        # Section content can also be accessed with the "self[name]" syntax,
        # which works with quoted properties like the ones above:
        alice_name: str = self["@alice:example.org"]  # result: Alice

        # Child sections are also accessible from "self":
        child_integer: int = self.Test.integer  # result: 5

        class Test:
            # "parent" refers to the section parent of this one, here "Names".
            alice_name: str = parent["@alice:example.org"]  # result: "Alice"
            integer:    int = parent.parent.integer_number  # Example.integer_number, which is 5

            # Top-level sections can also be accessed directly by names:
            alice_name_2: str = Example.Names["@alice:example.org"]
            integer_2:    int = Example.integer_number

Sections

Sections are defined like Python classes, and can contain properties, other sections, or Python functions.
A section's name should be written as CamelCase, and can only contain letters, digits and underscores.
The content of a section must be indented by that section's indentation plus four spaces:

class FirstSection:
    content_spaces: int = 0 + 4

    class SectionInsideFirst:
        content_spaces: int = 4 + 4

class SecondSection:
    content_spaces: int = 0 + 4

Empty sections can be created using the pass keyword:

class Empty:
    pass

Including Built-in Files

A section, including the file's root (which is treated as a section) can include files that are supplied by the application using the self.include_builtin(path) function.

path is the relative path to a file in the application's source folder, for example self.include_builtin("config/settings.py") refers to src/config/settings.py.

The sections and properties from the included file will be recursively merged, see Including User Files for an example.

Including User Files

Similar to including built-in files, user-written local files can be included with self.include_file(path), where path is an absolute or relative (from the current file's directory) file path.

Example with two files, a.py:

self.include_file("b.py")

class Shared:
    text:           str = "Sample"
    gets_overriden: str = "A"

    class FromA: 
        number: int = 1

and b.py:

class Shared:
    gets_overriden: str = "B"

    class FromB: 
        number: int = 2

This results in a merged PCN looking like so:

class Shared:
    text:           str = "Sample"
    gets_overriden: str = "B"

    class FromA: 
        number: int = 1

    class FromB: 
        number: int = 2

Include functions can also be used inside a section other than the root. If a.py had the include line inside Shared, the result would be:

class Shared:
    text:           str = "Sample"
    gets_overriden: str = "A"

    class FromA: 
        number: int = 1

    class Shared:
        gets_overriden: str = "B"

        class FromB: 
            number: int = 2

Inheritance

Like other Python classes, sections can inherit from other sections. Unlike including files, sections are not merged recursively.

This file:

class Mixin:
    first:  bool = True
    second: bool = False

class First(Mixin):
    pass

class Second(Mixin):
    third: int = 100

Would be equivalent to:

class First(Mixin):
    first:  bool = True
    second: bool = False

class Second(Mixin):
    first:  bool = True
    second: bool = False
    third:  int  = 100

Properties

Properties have a name, optional type annotation and value. Standard property names should be written in snake_case. In most cases, it is recommended to include type annotations, to make clear what a property's value should be:

    with_type:    int            = 3
    complex_type: Dict[str, int] = {"abc": 1, "def": 2, "ghi": 3}

    any_type: Any = None
    same_as_above = None

If the property's name starts with a digit or contains characters other than letters, digits or underscores, that name must be quoted:

"!alice:example.org" = "Alice"

Properties with these names can only be accessed by the brackets syntax.

Common types

• int: An integer number, e.g. 4.

• float: Floating point number, e.g. 4.5. Can also be an integer.

• str: String, a piece of text. If the text contains quotes or backslashes, escape them with a backslash. Other properties can be included by combining strings or using an f-string:

  escaped:  str = "C:\\Users\\Alice \"Foo\" Bar"
  number:   int = 1
  combined: str = "foo " + self.number
  fstring:  str = f"foo {number}"

• bool: Boolean, a value that can be either True or False.

• None: A None value, represents an absence of choice.

• Any: A value that can be of any type.

• list: List of values, e.g. [1, 2, 3].
  The type can be written as list or List[type] to specify what type the list's item should be.

• tuple: Similar to lists, but the length cannot be changed once created.
  Can be written as tuple, Tuple[type, type] to specify for example that the tuple must have two items of certain types, or Tuple[type, ...] for a tuple with any number of items of a certain same type:

  anything:     tuple                 = (1, 2, 3, "foo")
  many_ints:    Tuple[int, ...]       = (1, 2, 3, 4, 5)
  three_values: Tuple[int, str, bool] = (1, "example", False)

• dict: Mapping of keys to values. Can be written as dict or Dict[key_type, value_type]:

  anything:      dict           = {1: 2, "foo": "bar", True: 1.5}
  account_order: Dict[str, int] = {"@a:example.com": 1, "@b:example.com": 2}

• Optional[type]: A value that can be either that type or None

• Union[type1, type2]: A value that can be one of the type in the Union. The number of types can be more than two.

Expressions

A property's value can be any Python expression. Properties can also refer to other properties, no matter what section they belong to or what order they are defined in.

This PCN code:

class Section1:
    other: int = self.text.lower() * 2  # "exampleexample"
    text:  str = "Example"

Is roughly equivalent to this in standard Python:

class Section1:
    @property
    def other(self) -> str:
        return self.text.lower() * 2

    @property
    def text(self) -> str:
        return "Example"

Section Access

The current section and its properties are accessed via self:

class Base:
    number: int = 10
    other:  int = self.number * 2  # 20

The parent section is accessed via parent:

class Base:
    number: int = 10

    class Inner:
        number: int = parent.number * 2

Child sections can be accessed by self.SectionName:

class Base:
    number: int = self.Inner.number

    class Inner:
        number: int = 10

Any section (or property, or function) defined at the root/top-level of the file can be accessed by name:

class First:
    class InsideFirst:
        number: int = Second.number * 2  # 20
        other:  int = Second.InsideSecond.number  # 50

class Second:
    number: int = 10

    class InsideSecond:
        number: int = 50

The root (which behaves like a section) can also be explicitely accessed with self.root:

number: int = 10

class First:
    root_num: int = self.root.number  # Same as just saying "number"

class Second: 
    first_num: int = self.root.First.root_num  # Same as "First.root_num"

Bracket Access

Inner sections and properties can also be accessed by the section[name] syntax. This is the only way to access properties with non-standard names (as described in Properties):

class Names:
    "!alice:example.org": str = "alice"

    class Capitalized:
        alice: str = parent["!alice:example.org"].capitalize()  # "Alice"

The syntax can also be used to access properties dynamically:

class Names:
    alice:         str = "Alice"
    property_name: str = "alice"
    first_person:  str = self[property_name]

Top-level properties can only be accessed this way using self.root:

"!alice:example.org": str = "Alice"

class Names:
    alice: str = self.root["!alice:example.org"] = "Alice"

GUI Files

When properties for PCN files are edited from the user interface (programmatically or due to user actions), a separate file with a .gui.json extension is created in the same folder.

These files take priority and override properties from the equivalent user files. They should not be edited by hand. When a property in the user config file is edited, any equivalent property in the GUI file is automatically dropped, to let the user's setting apply again.