structured_data.enum

Complexity

Total Complexity

38

Size/Duplication

Total Lines	204
Duplicated Lines	0 %

Importance

Changes

0

7 Functions

Rating	Name	Duplication	Size	Complexity
A	_set_new_functions()	0	12	4
A	enum()	0	11	2
A	_name()	0	3	1
C	_args()	0	46	9
F	_process_class()	0	60	14
A	_make_nested_new()	0	7	2
A	_enum_super()	0	4	1

"""Class decorator for defining abstract data types."""

import ast
import sys
import typing
import weakref

import astor

from ._enum_constructor import make_constructor
from ._prewritten_methods import SUBCLASS_ORDER
from ._prewritten_methods import PrewrittenMethods

_CTOR_CACHE = {}


ARGS = weakref.WeakKeyDictionary()


class Ctor:
    """Marker class for enum constructors.

    To use, index with a sequence of types, and annotate a variable in an
    enum-decorated class with it.
    """

    def __new__(cls, args):
        if args == ():
            return cls
        self = object.__new__(cls)
        ARGS[self] = args
        return _CTOR_CACHE.setdefault(args, self)

    def __init_subclass__(cls, **kwargs):
        raise TypeError

    def __class_getitem__(cls, args):
        if not isinstance(args, tuple):
            args = (args,)
        return cls(args)


ARGS[Ctor] = ()


def _args(constructor, global_ns):
    # Handle forward declarations. Needed for 3.7 compatinility.
    if isinstance(constructor, str):
        # Leverage Python's parser instead of trying to parse by hand.
        ctor_ast = ast.parse(constructor, mode='eval')
        # The top-level operation must be a subscript, with normal indexing.
        if (
                isinstance(ctor_ast.body, ast.Subscript)
                and isinstance(ctor_ast.body.slice, ast.Index)):
            # Pull out the index argument
            index = ctor_ast.body.slice.value
            # This basically gets rid of the brackets and index.
            # Next, try to evaluate the result.
            # This relies on Ctor being globally visible at definition time,
            # which seems like a reasonable requirement.
            ctor_ast.body = ctor_ast.body.value
            try:
                value = eval(
                    compile(ctor_ast, '<annotation>', 'eval'), global_ns)
            except Exception:
                # We couldn't tell what it was, so it's probably not Ctor.
                return None
            if value is Ctor:
                # Pull the information directly off a Tuple node.
                if isinstance(index, ast.Tuple):
                    return tuple(astor.to_source(elt) for elt in index.elts)
                # Otherwise, assume it's a sequence of length 1.
                # It's possible for this heuristic to return false answers, BUT
                # it seems like everywhere that AST inspection and evaluation
                # disagree, it needs syntax that breaks mypy, so it's sort of
                # like it doesn't matter.
                return (astor.to_source(index),)
        try:
            # If the above conditions didn't hold, maybe it's an alias.
            # We could try to validate the AST, but we need to know the value
            # anyway if it's valid.
            constructor = eval(constructor, global_ns)
        except Exception:
            # This return is a little concerning. It's basically for "We tried
            # to evaluate a forward reference of some kind, and failed."
            # This might reject input at runtime that mypy would accept.
            # The basic solution is to document that you can have forward
            # references FROM a Ctor, but not within a decorated class.
            return None
    # Try to interpret the current value as a Ctor
    return ARGS.get(constructor)


def _name(cls, function) -> str:
    """Return the name of a function accessed through a descriptor."""
    return function.__get__(None, cls).__name__


def _set_new_functions(cls, *functions) -> typing.Optional[str]:
    """Attempt to set the attributes corresponding to the functions on cls.

    If any attributes are already defined, fail *before* setting any, and
    return the already-defined name.
    """
    for function in functions:
        if _name(cls, function) in cls.__dict__:
            return _name(cls, function)
    for function in functions:
        setattr(cls, _name(cls, function), function)
    return None


def _enum_super(_cls):
    def base(cls, args):
        return super(_cls, cls).__new__(cls, args)
    return base


def _make_nested_new(_cls, subclasses, base__new__):
    @staticmethod
    def __new__(cls, args):
        if cls not in subclasses:
            raise TypeError
        return base__new__(cls, args)
    return __new__


def _process_class(_cls, _repr, eq, order):
    if order and not eq:
        raise ValueError('eq must be true if order is true')

    argses = {}
    subclasses = set()
    subclass_order = []
    for cls in reversed(_cls.__mro__):
        for key, value in getattr(cls, '__annotations__', {}).items():
            args = _args(value, vars(sys.modules[cls.__module__]))
            # Shadow redone annotations.
            if args is None:
                argses.pop(key, None)
            else:
                argses[key] = args

    for name, args in argses.items():
        make_constructor(_cls, name, args, subclasses, subclass_order)

    _cls.__init_subclass__ = PrewrittenMethods.__init_subclass__

    if _set_new_functions(_cls, _make_nested_new(_cls, subclasses, _enum_super(_cls))):
        _cls.__new__ = _make_nested_new(_cls, subclasses, _cls.__new__)

    _set_new_functions(
        _cls, PrewrittenMethods.__setattr__, PrewrittenMethods.__delattr__)
    _set_new_functions(_cls, PrewrittenMethods.__bool__)

    if _repr:
        _set_new_functions(_cls, PrewrittenMethods.__repr__)

    equality_methods_were_set = False

    if eq:
        equality_methods_were_set = not _set_new_functions(
            _cls, PrewrittenMethods.__eq__, PrewrittenMethods.__ne__)

    if equality_methods_were_set:
        _cls.__hash__ = PrewrittenMethods.__hash__

    if order:
        if not equality_methods_were_set:
            raise ValueError(
                "Can't add ordering methods if equality methods are provided.")
        collision = _set_new_functions(
            _cls,
            PrewrittenMethods.__lt__,
            PrewrittenMethods.__le__,
            PrewrittenMethods.__gt__,
            PrewrittenMethods.__ge__
            )
        if collision:
            raise TypeError(
                'Cannot overwrite attribute {collision} in class '
                '{name}. Consider using functools.total_ordering'.format(
                    collision=collision, name=_cls.__name__))

    SUBCLASS_ORDER[_cls] = tuple(subclass_order)

    return _cls


def enum(_cls=None, *, repr=True, eq=True, order=False):
    """Decorate a class to be an algebraic data type."""

    def wrap(cls):
        """Return the processed class."""
        return _process_class(cls, repr, eq, order)

    if _cls is None:
        return wrap

    return wrap(_cls)


__all__ = ['Ctor', 'enum']