prefab-classes 0.7.5a3

Boilerplate Generator for Classes

PrefabClasses - Python Class Boilerplate Generator

Writes the class boilerplate code so you don't have to. Yet another variation on attrs/dataclasses.

Either written lazily when you first access the methods or eagerly when the class is compiled into a .pyc. Can optionally be made to rewrite .py source code with plain classes.

The dynamic method of evaluating lazily is more flexible, while the compiled method is faster (once the .pyc file has been generated).

For more detail look at the documentation.

Usage

Define the class using plain assignment and attribute function calls:

from prefab_classes import prefab, attribute

@prefab
class Settings:
    hostname = attribute(default="localhost")
    template_folder = attribute(default='base/path')
    template_name = attribute(default='index')

Or with type hinting:

from prefab_classes import prefab

@prefab
class Settings:
    hostname: str = "localhost"
    template_folder: str = 'base/path'
    template_name: str = 'index'

In either case the result behaves the same.

>>> from prefab_classes import to_json
>>> s = Settings()
>>> print(s)
Settings(hostname='localhost', template_folder='base/path', template_name='index')
>>> to_json(s)
'{"hostname": "localhost", "template_folder": "base/path", "template_name": "index"}'

For further details see the usage pages in the documentation.

How does it work

The @prefab decorator either rewrites the class dynamically, putting methods in place that will be generated as they are first accessed OR it acts as a marker to indicate the class should be transformed for the compiled classes.

Compiled classes can both be imported directly or converted back to new .py files. Direct import will perform the conversion before creating the .pyc file.

example.py

# COMPILE_PREFABS
from prefab_classes import prefab, attribute
from pathlib import Path


@prefab(compile_prefab=True)
class SettingsPath:
    hostname = attribute(default="localhost")
    template_folder = attribute(default='base/path')
    template_name = attribute(default='index')
    file_types = attribute(default_factory=list)

    def __prefab_post_init__(self, template_folder, file_types):
        self.template_folder = Path(template_folder)
        file_types.extend(['.md', '.html'])
        self.file_types = file_types

Direct import using prefab_compiler

from prefab_classes import prefab_compiler

with prefab_compiler():
    from example import SettingsPath

# Use normally from here

Compile to a new .py file using rewrite_to_py:

>>> from prefab_classes.compiled import rewrite_to_py
>>> rewrite_to_py('example.py', 'example_compiled.py', use_black=True, delete_firstlines=1)

Using black to format for ease of reading and deleting the now unused prefab imports.

example_compiled.py

# DO NOT MANUALLY EDIT THIS FILE
# MODULE: example_compiled.py
# GENERATED FROM: example.py
# USING prefab_classes VERSION: v0.7.2

from pathlib import Path


class SettingsPath:
    COMPILED = True
    PREFAB_FIELDS = ["hostname", "template_folder", "template_name", "file_types"]
    __match_args__ = ("hostname", "template_folder", "template_name", "file_types")

    def __init__(
        self,
        hostname="localhost",
        template_folder="base/path",
        template_name="index",
        file_types=None,
    ):
        self.hostname = hostname
        self.template_name = template_name
        file_types = file_types if file_types is not None else list()
        self.__prefab_post_init__(
            template_folder=template_folder, file_types=file_types
        )

    def __repr__(self):
        return f"{type(self).__qualname__}(hostname={self.hostname!r}, template_folder={self.template_folder!r}, template_name={self.template_name!r}, file_types={self.file_types!r})"

    def __eq__(self, other):
        return (
            (self.hostname, self.template_folder, self.template_name, self.file_types)
            == (
                other.hostname,
                other.template_folder,
                other.template_name,
                other.file_types,
            )
            if self.__class__ == other.__class__
            else NotImplemented
        )

    def __prefab_post_init__(self, template_folder, file_types):
        self.template_folder = Path(template_folder)
        file_types.extend([".md", ".html"])
        self.file_types = file_types

Why not just use attrs/dataclasses?

If attrs or dataclasses solves your problem then you should use them. They are thoroughly tested, well supported packages.

This project came about because I had a project which had 1 use of attrs and I was trying to reduce my dependencies. At the time I didn't like the requirerment for type hints in dataclasses and was looking at David Beazley's Cluegen as a potential replacement as it seemed easy to modify. I needed some additional features so I added them and it eventually lead to this project.

The autogen code and some of the method definitions for the dynamic classes still use the code from Cluegen.

Cluegen's lazy creation of the methods made me think about instead taking an eager construction, but doing it only once when the .py source is first compiled into a .pyc file by modifying the AST.

The benefit of this method is that once the source has been compiled to a .pyc file there is no longer any overhead from generating the class methods. The result is a normal python class as if it had been written by hand.

Credit

autogen function and some magic method definitions taken from David Beazley's Cluegen

General design based on previous experience using dataclasses and attrs.