basic subscriptions system

python/attr/__init__.py

@@ -0,0 +1,65 @@
+from __future__ import absolute_import, division, print_function
+
+from functools import partial
+
+from . import converters, exceptions, filters, validators
+from ._config import get_run_validators, set_run_validators
+from ._funcs import asdict, assoc, astuple, evolve, has
+from ._make import (
+    NOTHING,
+    Attribute,
+    Factory,
+    attrib,
+    attrs,
+    fields,
+    fields_dict,
+    make_class,
+    validate,
+)
+
+
+__version__ = "18.2.0"
+
+__title__ = "attrs"
+__description__ = "Classes Without Boilerplate"
+__url__ = "https://www.attrs.org/"
+__uri__ = __url__
+__doc__ = __description__ + " <" + __uri__ + ">"
+
+__author__ = "Hynek Schlawack"
+__email__ = "hs@ox.cx"
+
+__license__ = "MIT"
+__copyright__ = "Copyright (c) 2015 Hynek Schlawack"
+
+
+s = attributes = attrs
+ib = attr = attrib
+dataclass = partial(attrs, auto_attribs=True)  # happy Easter ;)
+
+__all__ = [
+    "Attribute",
+    "Factory",
+    "NOTHING",
+    "asdict",
+    "assoc",
+    "astuple",
+    "attr",
+    "attrib",
+    "attributes",
+    "attrs",
+    "converters",
+    "evolve",
+    "exceptions",
+    "fields",
+    "fields_dict",
+    "filters",
+    "get_run_validators",
+    "has",
+    "ib",
+    "make_class",
+    "s",
+    "set_run_validators",
+    "validate",
+    "validators",
+]

python/attr/__init__.pyi

@@ -0,0 +1,252 @@
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    Generic,
+    List,
+    Optional,
+    Sequence,
+    Mapping,
+    Tuple,
+    Type,
+    TypeVar,
+    Union,
+    overload,
+)
+
+# `import X as X` is required to make these public
+from . import exceptions as exceptions
+from . import filters as filters
+from . import converters as converters
+from . import validators as validators
+
+_T = TypeVar("_T")
+_C = TypeVar("_C", bound=type)
+
+_ValidatorType = Callable[[Any, Attribute, _T], Any]
+_ConverterType = Callable[[Any], _T]
+_FilterType = Callable[[Attribute, Any], bool]
+# FIXME: in reality, if multiple validators are passed they must be in a list or tuple,
+# but those are invariant and so would prevent subtypes of _ValidatorType from working
+# when passed in a list or tuple.
+_ValidatorArgType = Union[_ValidatorType[_T], Sequence[_ValidatorType[_T]]]
+
+# _make --
+
+NOTHING: object
+
+# NOTE: Factory lies about its return type to make this possible: `x: List[int] = Factory(list)`
+# Work around mypy issue #4554 in the common case by using an overload.
+@overload
+def Factory(factory: Callable[[], _T]) -> _T: ...
+@overload
+def Factory(
+    factory: Union[Callable[[Any], _T], Callable[[], _T]],
+    takes_self: bool = ...,
+) -> _T: ...
+
+class Attribute(Generic[_T]):
+    name: str
+    default: Optional[_T]
+    validator: Optional[_ValidatorType[_T]]
+    repr: bool
+    cmp: bool
+    hash: Optional[bool]
+    init: bool
+    converter: Optional[_ConverterType[_T]]
+    metadata: Dict[Any, Any]
+    type: Optional[Type[_T]]
+    kw_only: bool
+    def __lt__(self, x: Attribute) -> bool: ...
+    def __le__(self, x: Attribute) -> bool: ...
+    def __gt__(self, x: Attribute) -> bool: ...
+    def __ge__(self, x: Attribute) -> bool: ...
+
+# NOTE: We had several choices for the annotation to use for type arg:
+# 1) Type[_T]
+#   - Pros: Handles simple cases correctly
+#   - Cons: Might produce less informative errors in the case of conflicting TypeVars
+#   e.g. `attr.ib(default='bad', type=int)`
+# 2) Callable[..., _T]
+#   - Pros: Better error messages than #1 for conflicting TypeVars
+#   - Cons: Terrible error messages for validator checks.
+#   e.g. attr.ib(type=int, validator=validate_str)
+#        -> error: Cannot infer function type argument
+# 3) type (and do all of the work in the mypy plugin)
+#   - Pros: Simple here, and we could customize the plugin with our own errors.
+#   - Cons: Would need to write mypy plugin code to handle all the cases.
+# We chose option #1.
+
+# `attr` lies about its return type to make the following possible:
+#     attr()    -> Any
+#     attr(8)   -> int
+#     attr(validator=<some callable>)  -> Whatever the callable expects.
+# This makes this type of assignments possible:
+#     x: int = attr(8)
+#
+# This form catches explicit None or no default but with no other arguments returns Any.
+@overload
+def attrib(
+    default: None = ...,
+    validator: None = ...,
+    repr: bool = ...,
+    cmp: bool = ...,
+    hash: Optional[bool] = ...,
+    init: bool = ...,
+    convert: None = ...,
+    metadata: Optional[Mapping[Any, Any]] = ...,
+    type: None = ...,
+    converter: None = ...,
+    factory: None = ...,
+    kw_only: bool = ...,
+) -> Any: ...
+
+# This form catches an explicit None or no default and infers the type from the other arguments.
+@overload
+def attrib(
+    default: None = ...,
+    validator: Optional[_ValidatorArgType[_T]] = ...,
+    repr: bool = ...,
+    cmp: bool = ...,
+    hash: Optional[bool] = ...,
+    init: bool = ...,
+    convert: Optional[_ConverterType[_T]] = ...,
+    metadata: Optional[Mapping[Any, Any]] = ...,
+    type: Optional[Type[_T]] = ...,
+    converter: Optional[_ConverterType[_T]] = ...,
+    factory: Optional[Callable[[], _T]] = ...,
+    kw_only: bool = ...,
+) -> _T: ...
+
+# This form catches an explicit default argument.
+@overload
+def attrib(
+    default: _T,
+    validator: Optional[_ValidatorArgType[_T]] = ...,
+    repr: bool = ...,
+    cmp: bool = ...,
+    hash: Optional[bool] = ...,
+    init: bool = ...,
+    convert: Optional[_ConverterType[_T]] = ...,
+    metadata: Optional[Mapping[Any, Any]] = ...,
+    type: Optional[Type[_T]] = ...,
+    converter: Optional[_ConverterType[_T]] = ...,
+    factory: Optional[Callable[[], _T]] = ...,
+    kw_only: bool = ...,
+) -> _T: ...
+
+# This form covers type=non-Type: e.g. forward references (str), Any
+@overload
+def attrib(
+    default: Optional[_T] = ...,
+    validator: Optional[_ValidatorArgType[_T]] = ...,
+    repr: bool = ...,
+    cmp: bool = ...,
+    hash: Optional[bool] = ...,
+    init: bool = ...,
+    convert: Optional[_ConverterType[_T]] = ...,
+    metadata: Optional[Mapping[Any, Any]] = ...,
+    type: object = ...,
+    converter: Optional[_ConverterType[_T]] = ...,
+    factory: Optional[Callable[[], _T]] = ...,
+    kw_only: bool = ...,
+) -> Any: ...
+@overload
+def attrs(
+    maybe_cls: _C,
+    these: Optional[Dict[str, Any]] = ...,
+    repr_ns: Optional[str] = ...,
+    repr: bool = ...,
+    cmp: bool = ...,
+    hash: Optional[bool] = ...,
+    init: bool = ...,
+    slots: bool = ...,
+    frozen: bool = ...,
+    weakref_slot: bool = ...,
+    str: bool = ...,
+    auto_attribs: bool = ...,
+    kw_only: bool = ...,
+    cache_hash: bool = ...,
+) -> _C: ...
+@overload
+def attrs(
+    maybe_cls: None = ...,
+    these: Optional[Dict[str, Any]] = ...,
+    repr_ns: Optional[str] = ...,
+    repr: bool = ...,
+    cmp: bool = ...,
+    hash: Optional[bool] = ...,
+    init: bool = ...,
+    slots: bool = ...,
+    frozen: bool = ...,
+    weakref_slot: bool = ...,
+    str: bool = ...,
+    auto_attribs: bool = ...,
+    kw_only: bool = ...,
+    cache_hash: bool = ...,
+) -> Callable[[_C], _C]: ...
+
+# TODO: add support for returning NamedTuple from the mypy plugin
+class _Fields(Tuple[Attribute, ...]):
+    def __getattr__(self, name: str) -> Attribute: ...
+
+def fields(cls: type) -> _Fields: ...
+def fields_dict(cls: type) -> Dict[str, Attribute]: ...
+def validate(inst: Any) -> None: ...
+
+# TODO: add support for returning a proper attrs class from the mypy plugin
+# we use Any instead of _CountingAttr so that e.g. `make_class('Foo', [attr.ib()])` is valid
+def make_class(
+    name: str,
+    attrs: Union[List[str], Tuple[str, ...], Dict[str, Any]],
+    bases: Tuple[type, ...] = ...,
+    repr_ns: Optional[str] = ...,
+    repr: bool = ...,
+    cmp: bool = ...,
+    hash: Optional[bool] = ...,
+    init: bool = ...,
+    slots: bool = ...,
+    frozen: bool = ...,
+    weakref_slot: bool = ...,
+    str: bool = ...,
+    auto_attribs: bool = ...,
+    kw_only: bool = ...,
+    cache_hash: bool = ...,
+) -> type: ...
+
+# _funcs --
+
+# TODO: add support for returning TypedDict from the mypy plugin
+# FIXME: asdict/astuple do not honor their factory args.  waiting on one of these:
+# https://github.com/python/mypy/issues/4236
+# https://github.com/python/typing/issues/253
+def asdict(
+    inst: Any,
+    recurse: bool = ...,
+    filter: Optional[_FilterType] = ...,
+    dict_factory: Type[Mapping[Any, Any]] = ...,
+    retain_collection_types: bool = ...,
+) -> Dict[str, Any]: ...
+
+# TODO: add support for returning NamedTuple from the mypy plugin
+def astuple(
+    inst: Any,
+    recurse: bool = ...,
+    filter: Optional[_FilterType] = ...,
+    tuple_factory: Type[Sequence] = ...,
+    retain_collection_types: bool = ...,
+) -> Tuple[Any, ...]: ...
+def has(cls: type) -> bool: ...
+def assoc(inst: _T, **changes: Any) -> _T: ...
+def evolve(inst: _T, **changes: Any) -> _T: ...
+
+# _config --
+
+def set_run_validators(run: bool) -> None: ...
+def get_run_validators() -> bool: ...
+
+# aliases --
+
+s = attributes = attrs
+ib = attr = attrib
+dataclass = attrs  # Technically, partial(attrs, auto_attribs=True) ;)

python/attr/_compat.py

@@ -0,0 +1,163 @@
+from __future__ import absolute_import, division, print_function
+
+import platform
+import sys
+import types
+import warnings
+
+
+PY2 = sys.version_info[0] == 2
+PYPY = platform.python_implementation() == "PyPy"
+
+
+if PYPY or sys.version_info[:2] >= (3, 6):
+    ordered_dict = dict
+else:
+    from collections import OrderedDict
+
+    ordered_dict = OrderedDict
+
+
+if PY2:
+    from UserDict import IterableUserDict
+
+    # We 'bundle' isclass instead of using inspect as importing inspect is
+    # fairly expensive (order of 10-15 ms for a modern machine in 2016)
+    def isclass(klass):
+        return isinstance(klass, (type, types.ClassType))
+
+    # TYPE is used in exceptions, repr(int) is different on Python 2 and 3.
+    TYPE = "type"
+
+    def iteritems(d):
+        return d.iteritems()
+
+    # Python 2 is bereft of a read-only dict proxy, so we make one!
+    class ReadOnlyDict(IterableUserDict):
+        """
+        Best-effort read-only dict wrapper.
+        """
+
+        def __setitem__(self, key, val):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise TypeError(
+                "'mappingproxy' object does not support item assignment"
+            )
+
+        def update(self, _):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'update'"
+            )
+
+        def __delitem__(self, _):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise TypeError(
+                "'mappingproxy' object does not support item deletion"
+            )
+
+        def clear(self):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'clear'"
+            )
+
+        def pop(self, key, default=None):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'pop'"
+            )
+
+        def popitem(self):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'popitem'"
+            )
+
+        def setdefault(self, key, default=None):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'setdefault'"
+            )
+
+        def __repr__(self):
+            # Override to be identical to the Python 3 version.
+            return "mappingproxy(" + repr(self.data) + ")"
+
+    def metadata_proxy(d):
+        res = ReadOnlyDict()
+        res.data.update(d)  # We blocked update, so we have to do it like this.
+        return res
+
+
+else:
+
+    def isclass(klass):
+        return isinstance(klass, type)
+
+    TYPE = "class"
+
+    def iteritems(d):
+        return d.items()
+
+    def metadata_proxy(d):
+        return types.MappingProxyType(dict(d))
+
+
+def import_ctypes():
+    """
+    Moved into a function for testability.
+    """
+    import ctypes
+
+    return ctypes
+
+
+if not PY2:
+
+    def just_warn(*args, **kw):
+        """
+        We only warn on Python 3 because we are not aware of any concrete
+        consequences of not setting the cell on Python 2.
+        """
+        warnings.warn(
+            "Missing ctypes.  Some features like bare super() or accessing "
+            "__class__ will not work with slots classes.",
+            RuntimeWarning,
+            stacklevel=2,
+        )
+
+
+else:
+
+    def just_warn(*args, **kw):  # pragma: nocover
+        """
+        We only warn on Python 3 because we are not aware of any concrete
+        consequences of not setting the cell on Python 2.
+        """
+
+
+def make_set_closure_cell():
+    """
+    Moved into a function for testability.
+    """
+    if PYPY:  # pragma: no cover
+
+        def set_closure_cell(cell, value):
+            cell.__setstate__((value,))
+
+    else:
+        try:
+            ctypes = import_ctypes()
+
+            set_closure_cell = ctypes.pythonapi.PyCell_Set
+            set_closure_cell.argtypes = (ctypes.py_object, ctypes.py_object)
+            set_closure_cell.restype = ctypes.c_int
+        except Exception:
+            # We try best effort to set the cell, but sometimes it's not
+            # possible.  For example on Jython or on GAE.
+            set_closure_cell = just_warn
+    return set_closure_cell
+
+
+set_closure_cell = make_set_closure_cell()

python/attr/_config.py

@@ -0,0 +1,23 @@
+from __future__ import absolute_import, division, print_function
+
+
+__all__ = ["set_run_validators", "get_run_validators"]
+
+_run_validators = True
+
+
+def set_run_validators(run):
+    """
+    Set whether or not validators are run.  By default, they are run.
+    """
+    if not isinstance(run, bool):
+        raise TypeError("'run' must be bool.")
+    global _run_validators
+    _run_validators = run
+
+
+def get_run_validators():
+    """
+    Return whether or not validators are run.
+    """
+    return _run_validators

python/attr/_funcs.py

@@ -0,0 +1,290 @@
+from __future__ import absolute_import, division, print_function
+
+import copy
+
+from ._compat import iteritems
+from ._make import NOTHING, _obj_setattr, fields
+from .exceptions import AttrsAttributeNotFoundError
+
+
+def asdict(
+    inst,
+    recurse=True,
+    filter=None,
+    dict_factory=dict,
+    retain_collection_types=False,
+):
+    """
+    Return the ``attrs`` attribute values of *inst* as a dict.
+
+    Optionally recurse into other ``attrs``-decorated classes.
+
+    :param inst: Instance of an ``attrs``-decorated class.
+    :param bool recurse: Recurse into classes that are also
+        ``attrs``-decorated.
+    :param callable filter: A callable whose return code determines whether an
+        attribute or element is included (``True``) or dropped (``False``).  Is
+        called with the :class:`attr.Attribute` as the first argument and the
+        value as the second argument.
+    :param callable dict_factory: A callable to produce dictionaries from.  For
+        example, to produce ordered dictionaries instead of normal Python
+        dictionaries, pass in ``collections.OrderedDict``.
+    :param bool retain_collection_types: Do not convert to ``list`` when
+        encountering an attribute whose type is ``tuple`` or ``set``.  Only
+        meaningful if ``recurse`` is ``True``.
+
+    :rtype: return type of *dict_factory*
+
+    :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs``
+        class.
+
+    ..  versionadded:: 16.0.0 *dict_factory*
+    ..  versionadded:: 16.1.0 *retain_collection_types*
+    """
+    attrs = fields(inst.__class__)
+    rv = dict_factory()
+    for a in attrs:
+        v = getattr(inst, a.name)
+        if filter is not None and not filter(a, v):
+            continue
+        if recurse is True:
+            if has(v.__class__):
+                rv[a.name] = asdict(
+                    v, True, filter, dict_factory, retain_collection_types
+                )
+            elif isinstance(v, (tuple, list, set)):
+                cf = v.__class__ if retain_collection_types is True else list
+                rv[a.name] = cf(
+                    [
+                        _asdict_anything(
+                            i, filter, dict_factory, retain_collection_types
+                        )
+                        for i in v
+                    ]
+                )
+            elif isinstance(v, dict):
+                df = dict_factory
+                rv[a.name] = df(
+                    (
+                        _asdict_anything(
+                            kk, filter, df, retain_collection_types
+                        ),
+                        _asdict_anything(
+                            vv, filter, df, retain_collection_types
+                        ),
+                    )
+                    for kk, vv in iteritems(v)
+                )
+            else:
+                rv[a.name] = v
+        else:
+            rv[a.name] = v
+    return rv
+
+
+def _asdict_anything(val, filter, dict_factory, retain_collection_types):
+    """
+    ``asdict`` only works on attrs instances, this works on anything.
+    """
+    if getattr(val.__class__, "__attrs_attrs__", None) is not None:
+        # Attrs class.
+        rv = asdict(val, True, filter, dict_factory, retain_collection_types)
+    elif isinstance(val, (tuple, list, set)):
+        cf = val.__class__ if retain_collection_types is True else list
+        rv = cf(
+            [
+                _asdict_anything(
+                    i, filter, dict_factory, retain_collection_types
+                )
+                for i in val
+            ]
+        )
+    elif isinstance(val, dict):
+        df = dict_factory
+        rv = df(
+            (
+                _asdict_anything(kk, filter, df, retain_collection_types),
+                _asdict_anything(vv, filter, df, retain_collection_types),
+            )
+            for kk, vv in iteritems(val)
+        )
+    else:
+        rv = val
+    return rv
+
+
+def astuple(
+    inst,
+    recurse=True,
+    filter=None,
+    tuple_factory=tuple,
+    retain_collection_types=False,
+):
+    """
+    Return the ``attrs`` attribute values of *inst* as a tuple.
+
+    Optionally recurse into other ``attrs``-decorated classes.
+
+    :param inst: Instance of an ``attrs``-decorated class.
+    :param bool recurse: Recurse into classes that are also
+        ``attrs``-decorated.
+    :param callable filter: A callable whose return code determines whether an
+        attribute or element is included (``True``) or dropped (``False``).  Is
+        called with the :class:`attr.Attribute` as the first argument and the
+        value as the second argument.
+    :param callable tuple_factory: A callable to produce tuples from.  For
+        example, to produce lists instead of tuples.
+    :param bool retain_collection_types: Do not convert to ``list``
+        or ``dict`` when encountering an attribute which type is
+        ``tuple``, ``dict`` or ``set``.  Only meaningful if ``recurse`` is
+        ``True``.
+
+    :rtype: return type of *tuple_factory*
+
+    :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs``
+        class.
+
+    ..  versionadded:: 16.2.0
+    """
+    attrs = fields(inst.__class__)
+    rv = []
+    retain = retain_collection_types  # Very long. :/
+    for a in attrs:
+        v = getattr(inst, a.name)
+        if filter is not None and not filter(a, v):
+            continue
+        if recurse is True:
+            if has(v.__class__):
+                rv.append(
+                    astuple(
+                        v,
+                        recurse=True,
+                        filter=filter,
+                        tuple_factory=tuple_factory,
+                        retain_collection_types=retain,
+                    )
+                )
+            elif isinstance(v, (tuple, list, set)):
+                cf = v.__class__ if retain is True else list
+                rv.append(
+                    cf(
+                        [
+                            astuple(
+                                j,
+                                recurse=True,
+                                filter=filter,
+                                tuple_factory=tuple_factory,
+                                retain_collection_types=retain,
+                            )
+                            if has(j.__class__)
+                            else j
+                            for j in v
+                        ]
+                    )
+                )
+            elif isinstance(v, dict):
+                df = v.__class__ if retain is True else dict
+                rv.append(
+                    df(
+                        (
+                            astuple(
+                                kk,
+                                tuple_factory=tuple_factory,
+                                retain_collection_types=retain,
+                            )
+                            if has(kk.__class__)
+                            else kk,
+                            astuple(
+                                vv,
+                                tuple_factory=tuple_factory,
+                                retain_collection_types=retain,
+                            )
+                            if has(vv.__class__)
+                            else vv,
+                        )
+                        for kk, vv in iteritems(v)
+                    )
+                )
+            else:
+                rv.append(v)
+        else:
+            rv.append(v)
+    return rv if tuple_factory is list else tuple_factory(rv)
+
+
+def has(cls):
+    """
+    Check whether *cls* is a class with ``attrs`` attributes.
+
+    :param type cls: Class to introspect.
+    :raise TypeError: If *cls* is not a class.
+
+    :rtype: :class:`bool`
+    """
+    return getattr(cls, "__attrs_attrs__", None) is not None
+
+
+def assoc(inst, **changes):
+    """
+    Copy *inst* and apply *changes*.
+
+    :param inst: Instance of a class with ``attrs`` attributes.
+    :param changes: Keyword changes in the new copy.
+
+    :return: A copy of inst with *changes* incorporated.
+
+    :raise attr.exceptions.AttrsAttributeNotFoundError: If *attr_name* couldn't
+        be found on *cls*.
+    :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs``
+        class.
+
+    ..  deprecated:: 17.1.0
+        Use :func:`evolve` instead.
+    """
+    import warnings
+
+    warnings.warn(
+        "assoc is deprecated and will be removed after 2018/01.",
+        DeprecationWarning,
+        stacklevel=2,
+    )
+    new = copy.copy(inst)
+    attrs = fields(inst.__class__)
+    for k, v in iteritems(changes):
+        a = getattr(attrs, k, NOTHING)
+        if a is NOTHING:
+            raise AttrsAttributeNotFoundError(
+                "{k} is not an attrs attribute on {cl}.".format(
+                    k=k, cl=new.__class__
+                )
+            )
+        _obj_setattr(new, k, v)
+    return new
+
+
+def evolve(inst, **changes):
+    """
+    Create a new instance, based on *inst* with *changes* applied.
+
+    :param inst: Instance of a class with ``attrs`` attributes.
+    :param changes: Keyword changes in the new copy.
+
+    :return: A copy of inst with *changes* incorporated.
+
+    :raise TypeError: If *attr_name* couldn't be found in the class
+        ``__init__``.
+    :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs``
+        class.
+
+    ..  versionadded:: 17.1.0
+    """
+    cls = inst.__class__
+    attrs = fields(cls)
+    for a in attrs:
+        if not a.init:
+            continue
+        attr_name = a.name  # To deal with private attributes.
+        init_name = attr_name if attr_name[0] != "_" else attr_name[1:]
+        if init_name not in changes:
+            changes[init_name] = getattr(inst, attr_name)
+    return cls(**changes)

python/attr/converters.py

@@ -0,0 +1,78 @@
+"""
+Commonly useful converters.
+"""
+
+from __future__ import absolute_import, division, print_function
+
+from ._make import NOTHING, Factory
+
+
+def optional(converter):
+    """
+    A converter that allows an attribute to be optional. An optional attribute
+    is one which can be set to ``None``.
+
+    :param callable converter: the converter that is used for non-``None``
+        values.
+
+    .. versionadded:: 17.1.0
+    """
+
+    def optional_converter(val):
+        if val is None:
+            return None
+        return converter(val)
+
+    return optional_converter
+
+
+def default_if_none(default=NOTHING, factory=None):
+    """
+    A converter that allows to replace ``None`` values by *default* or the
+    result of *factory*.
+
+    :param default: Value to be used if ``None`` is passed. Passing an instance
+       of :class:`attr.Factory` is supported, however the ``takes_self`` option
+       is *not*.
+    :param callable factory: A callable that takes not parameters whose result
+       is used if ``None`` is passed.
+
+    :raises TypeError: If **neither** *default* or *factory* is passed.
+    :raises TypeError: If **both** *default* and *factory* are passed.
+    :raises ValueError: If an instance of :class:`attr.Factory` is passed with
+       ``takes_self=True``.
+
+    .. versionadded:: 18.2.0
+    """
+    if default is NOTHING and factory is None:
+        raise TypeError("Must pass either `default` or `factory`.")
+
+    if default is not NOTHING and factory is not None:
+        raise TypeError(
+            "Must pass either `default` or `factory` but not both."
+        )
+
+    if factory is not None:
+        default = Factory(factory)
+
+    if isinstance(default, Factory):
+        if default.takes_self:
+            raise ValueError(
+                "`takes_self` is not supported by default_if_none."
+            )
+
+        def default_if_none_converter(val):
+            if val is not None:
+                return val
+
+            return default.factory()
+
+    else:
+
+        def default_if_none_converter(val):
+            if val is not None:
+                return val
+
+            return default
+
+    return default_if_none_converter

python/attr/converters.pyi

@@ -0,0 +1,12 @@
+from typing import TypeVar, Optional, Callable, overload
+from . import _ConverterType
+
+_T = TypeVar("_T")
+
+def optional(
+    converter: _ConverterType[_T]
+) -> _ConverterType[Optional[_T]]: ...
+@overload
+def default_if_none(default: _T) -> _ConverterType[_T]: ...
+@overload
+def default_if_none(*, factory: Callable[[], _T]) -> _ConverterType[_T]: ...

python/attr/exceptions.py

@@ -0,0 +1,57 @@
+from __future__ import absolute_import, division, print_function
+
+
+class FrozenInstanceError(AttributeError):
+    """
+    A frozen/immutable instance has been attempted to be modified.
+
+    It mirrors the behavior of ``namedtuples`` by using the same error message
+    and subclassing :exc:`AttributeError`.
+
+    .. versionadded:: 16.1.0
+    """
+
+    msg = "can't set attribute"
+    args = [msg]
+
+
+class AttrsAttributeNotFoundError(ValueError):
+    """
+    An ``attrs`` function couldn't find an attribute that the user asked for.
+
+    .. versionadded:: 16.2.0
+    """
+
+
+class NotAnAttrsClassError(ValueError):
+    """
+    A non-``attrs`` class has been passed into an ``attrs`` function.
+
+    .. versionadded:: 16.2.0
+    """
+
+
+class DefaultAlreadySetError(RuntimeError):
+    """
+    A default has been set using ``attr.ib()`` and is attempted to be reset
+    using the decorator.
+
+    .. versionadded:: 17.1.0
+    """
+
+
+class UnannotatedAttributeError(RuntimeError):
+    """
+    A class with ``auto_attribs=True`` has an ``attr.ib()`` without a type
+    annotation.
+
+    .. versionadded:: 17.3.0
+    """
+
+
+class PythonTooOldError(RuntimeError):
+    """
+    An ``attrs`` feature requiring a more recent python version has been used.
+
+    .. versionadded:: 18.2.0
+    """

python/attr/exceptions.pyi

@@ -0,0 +1,7 @@
+class FrozenInstanceError(AttributeError):
+    msg: str = ...
+
+class AttrsAttributeNotFoundError(ValueError): ...
+class NotAnAttrsClassError(ValueError): ...
+class DefaultAlreadySetError(RuntimeError): ...
+class UnannotatedAttributeError(RuntimeError): ...

python/attr/filters.py

@@ -0,0 +1,52 @@
+"""
+Commonly useful filters for :func:`attr.asdict`.
+"""
+
+from __future__ import absolute_import, division, print_function
+
+from ._compat import isclass
+from ._make import Attribute
+
+
+def _split_what(what):
+    """
+    Returns a tuple of `frozenset`s of classes and attributes.
+    """
+    return (
+        frozenset(cls for cls in what if isclass(cls)),
+        frozenset(cls for cls in what if isinstance(cls, Attribute)),
+    )
+
+
+def include(*what):
+    """
+    Whitelist *what*.
+
+    :param what: What to whitelist.
+    :type what: :class:`list` of :class:`type` or :class:`attr.Attribute`\\ s
+
+    :rtype: :class:`callable`
+    """
+    cls, attrs = _split_what(what)
+
+    def include_(attribute, value):
+        return value.__class__ in cls or attribute in attrs
+
+    return include_
+
+
+def exclude(*what):
+    """
+    Blacklist *what*.
+
+    :param what: What to blacklist.
+    :type what: :class:`list` of classes or :class:`attr.Attribute`\\ s.
+
+    :rtype: :class:`callable`
+    """
+    cls, attrs = _split_what(what)
+
+    def exclude_(attribute, value):
+        return value.__class__ not in cls and attribute not in attrs
+
+    return exclude_

python/attr/filters.pyi

@@ -0,0 +1,5 @@
+from typing import Union
+from . import Attribute, _FilterType
+
+def include(*what: Union[type, Attribute]) -> _FilterType: ...
+def exclude(*what: Union[type, Attribute]) -> _FilterType: ...

python/attr/validators.py

@@ -0,0 +1,170 @@
+"""
+Commonly useful validators.
+"""
+
+from __future__ import absolute_import, division, print_function
+
+from ._make import _AndValidator, and_, attrib, attrs
+
+
+__all__ = ["and_", "in_", "instance_of", "optional", "provides"]
+
+
+@attrs(repr=False, slots=True, hash=True)
+class _InstanceOfValidator(object):
+    type = attrib()
+
+    def __call__(self, inst, attr, value):
+        """
+        We use a callable class to be able to change the ``__repr__``.
+        """
+        if not isinstance(value, self.type):
+            raise TypeError(
+                "'{name}' must be {type!r} (got {value!r} that is a "
+                "{actual!r}).".format(
+                    name=attr.name,
+                    type=self.type,
+                    actual=value.__class__,
+                    value=value,
+                ),
+                attr,
+                self.type,
+                value,
+            )
+
+    def __repr__(self):
+        return "<instance_of validator for type {type!r}>".format(
+            type=self.type
+        )
+
+
+def instance_of(type):
+    """
+    A validator that raises a :exc:`TypeError` if the initializer is called
+    with a wrong type for this particular attribute (checks are performed using
+    :func:`isinstance` therefore it's also valid to pass a tuple of types).
+
+    :param type: The type to check for.
+    :type type: type or tuple of types
+
+    :raises TypeError: With a human readable error message, the attribute
+        (of type :class:`attr.Attribute`), the expected type, and the value it
+        got.
+    """
+    return _InstanceOfValidator(type)
+
+
+@attrs(repr=False, slots=True, hash=True)
+class _ProvidesValidator(object):
+    interface = attrib()
+
+    def __call__(self, inst, attr, value):
+        """
+        We use a callable class to be able to change the ``__repr__``.
+        """
+        if not self.interface.providedBy(value):
+            raise TypeError(
+                "'{name}' must provide {interface!r} which {value!r} "
+                "doesn't.".format(
+                    name=attr.name, interface=self.interface, value=value
+                ),
+                attr,
+                self.interface,
+                value,
+            )
+
+    def __repr__(self):
+        return "<provides validator for interface {interface!r}>".format(
+            interface=self.interface
+        )
+
+
+def provides(interface):
+    """
+    A validator that raises a :exc:`TypeError` if the initializer is called
+    with an object that does not provide the requested *interface* (checks are
+    performed using ``interface.providedBy(value)`` (see `zope.interface
+    <https://zopeinterface.readthedocs.io/en/latest/>`_).
+
+    :param zope.interface.Interface interface: The interface to check for.
+
+    :raises TypeError: With a human readable error message, the attribute
+        (of type :class:`attr.Attribute`), the expected interface, and the
+        value it got.
+    """
+    return _ProvidesValidator(interface)
+
+
+@attrs(repr=False, slots=True, hash=True)
+class _OptionalValidator(object):
+    validator = attrib()
+
+    def __call__(self, inst, attr, value):
+        if value is None:
+            return
+
+        self.validator(inst, attr, value)
+
+    def __repr__(self):
+        return "<optional validator for {what} or None>".format(
+            what=repr(self.validator)
+        )
+
+
+def optional(validator):
+    """
+    A validator that makes an attribute optional.  An optional attribute is one
+    which can be set to ``None`` in addition to satisfying the requirements of
+    the sub-validator.
+
+    :param validator: A validator (or a list of validators) that is used for
+        non-``None`` values.
+    :type validator: callable or :class:`list` of callables.
+
+    .. versionadded:: 15.1.0
+    .. versionchanged:: 17.1.0 *validator* can be a list of validators.
+    """
+    if isinstance(validator, list):
+        return _OptionalValidator(_AndValidator(validator))
+    return _OptionalValidator(validator)
+
+
+@attrs(repr=False, slots=True, hash=True)
+class _InValidator(object):
+    options = attrib()
+
+    def __call__(self, inst, attr, value):
+        try:
+            in_options = value in self.options
+        except TypeError as e:  # e.g. `1 in "abc"`
+            in_options = False
+
+        if not in_options:
+            raise ValueError(
+                "'{name}' must be in {options!r} (got {value!r})".format(
+                    name=attr.name, options=self.options, value=value
+                )
+            )
+
+    def __repr__(self):
+        return "<in_ validator with options {options!r}>".format(
+            options=self.options
+        )
+
+
+def in_(options):
+    """
+    A validator that raises a :exc:`ValueError` if the initializer is called
+    with a value that does not belong in the options provided.  The check is
+    performed using ``value in options``.
+
+    :param options: Allowed options.
+    :type options: list, tuple, :class:`enum.Enum`, ...
+
+    :raises ValueError: With a human readable error message, the attribute (of
+       type :class:`attr.Attribute`), the expected options, and the value it
+       got.
+
+    .. versionadded:: 17.1.0
+    """
+    return _InValidator(options)

python/attr/validators.pyi

@@ -0,0 +1,14 @@
+from typing import Container, List, Union, TypeVar, Type, Any, Optional, Tuple
+from . import _ValidatorType
+
+_T = TypeVar("_T")
+
+def instance_of(
+    type: Union[Tuple[Type[_T], ...], Type[_T]]
+) -> _ValidatorType[_T]: ...
+def provides(interface: Any) -> _ValidatorType[Any]: ...
+def optional(
+    validator: Union[_ValidatorType[_T], List[_ValidatorType[_T]]]
+) -> _ValidatorType[Optional[_T]]: ...
+def in_(options: Container[_T]) -> _ValidatorType[_T]: ...
+def and_(*validators: _ValidatorType[_T]) -> _ValidatorType[_T]: ...