view mercurial/thirdparty/attr/_make.py @ 42378:c3484ddbdb96 stable 5.0.1

manifest: add some documentation to _lazymanifest python code

It was not particularly easy figuring out the design of this class and keeping
track of how the pieces work.  So might as well write some of it down for the
next person.

from __future__ import absolute_import, division, print_function

import hashlib
import linecache

from operator import itemgetter

from . import _config
from ._compat import PY2, iteritems, isclass, iterkeys, metadata_proxy
from .exceptions import (
    DefaultAlreadySetError,
    FrozenInstanceError,
    NotAnAttrsClassError,
)


# This is used at least twice, so cache it here.
_obj_setattr = object.__setattr__
_init_convert_pat = "__attr_convert_{}"
_init_factory_pat = "__attr_factory_{}"
_tuple_property_pat = "    {attr_name} = property(itemgetter({index}))"
_empty_metadata_singleton = metadata_proxy({})


class _Nothing(object):
    """
    Sentinel class to indicate the lack of a value when ``None`` is ambiguous.

    All instances of `_Nothing` are equal.
    """
    def __copy__(self):
        return self

    def __deepcopy__(self, _):
        return self

    def __eq__(self, other):
        return other.__class__ == _Nothing

    def __ne__(self, other):
        return not self == other

    def __repr__(self):
        return "NOTHING"

    def __hash__(self):
        return 0xdeadbeef


NOTHING = _Nothing()
"""
Sentinel to indicate the lack of a value when ``None`` is ambiguous.
"""


def attr(default=NOTHING, validator=None,
         repr=True, cmp=True, hash=None, init=True,
         convert=None, metadata={}):
    r"""
    Create a new attribute on a class.

    ..  warning::

        Does *not* do anything unless the class is also decorated with
        :func:`attr.s`!

    :param default: A value that is used if an ``attrs``-generated ``__init__``
        is used and no value is passed while instantiating or the attribute is
        excluded using ``init=False``.

        If the value is an instance of :class:`Factory`, its callable will be
        used to construct a new value (useful for mutable datatypes like lists
        or dicts).

        If a default is not set (or set manually to ``attr.NOTHING``), a value
        *must* be supplied when instantiating; otherwise a :exc:`TypeError`
        will be raised.

        The default can also be set using decorator notation as shown below.

    :type default: Any value.

    :param validator: :func:`callable` that is called by ``attrs``-generated
        ``__init__`` methods after the instance has been initialized.  They
        receive the initialized instance, the :class:`Attribute`, and the
        passed value.

        The return value is *not* inspected so the validator has to throw an
        exception itself.

        If a ``list`` is passed, its items are treated as validators and must
        all pass.

        Validators can be globally disabled and re-enabled using
        :func:`get_run_validators`.

        The validator can also be set using decorator notation as shown below.

    :type validator: ``callable`` or a ``list`` of ``callable``\ s.

    :param bool repr: Include this attribute in the generated ``__repr__``
        method.
    :param bool cmp: Include this attribute in the generated comparison methods
        (``__eq__`` et al).
    :param hash: Include this attribute in the generated ``__hash__``
        method.  If ``None`` (default), mirror *cmp*'s value.  This is the
        correct behavior according the Python spec.  Setting this value to
        anything else than ``None`` is *discouraged*.
    :type hash: ``bool`` or ``None``
    :param bool init: Include this attribute in the generated ``__init__``
        method.  It is possible to set this to ``False`` and set a default
        value.  In that case this attributed is unconditionally initialized
        with the specified default value or factory.
    :param callable convert: :func:`callable` that is called by
        ``attrs``-generated ``__init__`` methods to convert attribute's value
        to the desired format.  It is given the passed-in value, and the
        returned value will be used as the new value of the attribute.  The
        value is converted before being passed to the validator, if any.
    :param metadata: An arbitrary mapping, to be used by third-party
        components.  See :ref:`extending_metadata`.

    ..  versionchanged:: 17.1.0 *validator* can be a ``list`` now.
    ..  versionchanged:: 17.1.0
        *hash* is ``None`` and therefore mirrors *cmp* by default .
    """
    if hash is not None and hash is not True and hash is not False:
        raise TypeError(
            "Invalid value for hash.  Must be True, False, or None."
        )
    return _CountingAttr(
        default=default,
        validator=validator,
        repr=repr,
        cmp=cmp,
        hash=hash,
        init=init,
        convert=convert,
        metadata=metadata,
    )


def _make_attr_tuple_class(cls_name, attr_names):
    """
    Create a tuple subclass to hold `Attribute`s for an `attrs` class.

    The subclass is a bare tuple with properties for names.

    class MyClassAttributes(tuple):
        __slots__ = ()
        x = property(itemgetter(0))
    """
    attr_class_name = "{}Attributes".format(cls_name)
    attr_class_template = [
        "class {}(tuple):".format(attr_class_name),
        "    __slots__ = ()",
    ]
    if attr_names:
        for i, attr_name in enumerate(attr_names):
            attr_class_template.append(_tuple_property_pat.format(
                index=i,
                attr_name=attr_name,
            ))
    else:
        attr_class_template.append("    pass")
    globs = {"itemgetter": itemgetter}
    eval(compile("\n".join(attr_class_template), "", "exec"), globs)
    return globs[attr_class_name]


def _transform_attrs(cls, these):
    """
    Transforms all `_CountingAttr`s on a class into `Attribute`s and saves the
    list in `__attrs_attrs__`.

    If *these* is passed, use that and don't look for them on the class.
    """
    super_cls = []
    for c in reversed(cls.__mro__[1:-1]):
        sub_attrs = getattr(c, "__attrs_attrs__", None)
        if sub_attrs is not None:
            super_cls.extend(a for a in sub_attrs if a not in super_cls)
    if these is None:
        ca_list = [(name, attr)
                   for name, attr
                   in cls.__dict__.items()
                   if isinstance(attr, _CountingAttr)]
    else:
        ca_list = [(name, ca)
                   for name, ca
                   in iteritems(these)]

    non_super_attrs = [
        Attribute.from_counting_attr(name=attr_name, ca=ca)
        for attr_name, ca
        in sorted(ca_list, key=lambda e: e[1].counter)
    ]
    attr_names = [a.name for a in super_cls + non_super_attrs]

    AttrsClass = _make_attr_tuple_class(cls.__name__, attr_names)

    cls.__attrs_attrs__ = AttrsClass(super_cls + [
        Attribute.from_counting_attr(name=attr_name, ca=ca)
        for attr_name, ca
        in sorted(ca_list, key=lambda e: e[1].counter)
    ])

    had_default = False
    for a in cls.__attrs_attrs__:
        if these is None and a not in super_cls:
            setattr(cls, a.name, a)
        if had_default is True and a.default is NOTHING and a.init is True:
            raise ValueError(
                "No mandatory attributes allowed after an attribute with a "
                "default value or factory.  Attribute in question: {a!r}"
                .format(a=a)
            )
        elif had_default is False and \
                a.default is not NOTHING and \
                a.init is not False:
            had_default = True


def _frozen_setattrs(self, name, value):
    """
    Attached to frozen classes as __setattr__.
    """
    raise FrozenInstanceError()


def _frozen_delattrs(self, name):
    """
    Attached to frozen classes as __delattr__.
    """
    raise FrozenInstanceError()


def attributes(maybe_cls=None, these=None, repr_ns=None,
               repr=True, cmp=True, hash=None, init=True,
               slots=False, frozen=False, str=False):
    r"""
    A class decorator that adds `dunder
    <https://wiki.python.org/moin/DunderAlias>`_\ -methods according to the
    specified attributes using :func:`attr.ib` or the *these* argument.

    :param these: A dictionary of name to :func:`attr.ib` mappings.  This is
        useful to avoid the definition of your attributes within the class body
        because you can't (e.g. if you want to add ``__repr__`` methods to
        Django models) or don't want to.

        If *these* is not ``None``, ``attrs`` will *not* search the class body
        for attributes.

    :type these: :class:`dict` of :class:`str` to :func:`attr.ib`

    :param str repr_ns: When using nested classes, there's no way in Python 2
        to automatically detect that.  Therefore it's possible to set the
        namespace explicitly for a more meaningful ``repr`` output.
    :param bool repr: Create a ``__repr__`` method with a human readable
        represantation of ``attrs`` attributes..
    :param bool str: Create a ``__str__`` method that is identical to
        ``__repr__``.  This is usually not necessary except for
        :class:`Exception`\ s.
    :param bool cmp: Create ``__eq__``, ``__ne__``, ``__lt__``, ``__le__``,
        ``__gt__``, and ``__ge__`` methods that compare the class as if it were
        a tuple of its ``attrs`` attributes.  But the attributes are *only*
        compared, if the type of both classes is *identical*!
    :param hash: If ``None`` (default), the ``__hash__`` method is generated
        according how *cmp* and *frozen* are set.

        1. If *both* are True, ``attrs`` will generate a ``__hash__`` for you.
        2. If *cmp* is True and *frozen* is False, ``__hash__`` will be set to
           None, marking it unhashable (which it is).
        3. If *cmp* is False, ``__hash__`` will be left untouched meaning the
           ``__hash__`` method of the superclass will be used (if superclass is
           ``object``, this means it will fall back to id-based hashing.).

        Although not recommended, you can decide for yourself and force
        ``attrs`` to create one (e.g. if the class is immutable even though you
        didn't freeze it programmatically) by passing ``True`` or not.  Both of
        these cases are rather special and should be used carefully.

        See the `Python documentation \
        <https://docs.python.org/3/reference/datamodel.html#object.__hash__>`_
        and the `GitHub issue that led to the default behavior \
        <https://github.com/python-attrs/attrs/issues/136>`_ for more details.
    :type hash: ``bool`` or ``None``
    :param bool init: Create a ``__init__`` method that initialiazes the
        ``attrs`` attributes.  Leading underscores are stripped for the
        argument name.  If a ``__attrs_post_init__`` method exists on the
        class, it will be called after the class is fully initialized.
    :param bool slots: Create a slots_-style class that's more
        memory-efficient.  See :ref:`slots` for further ramifications.
    :param bool frozen: Make instances immutable after initialization.  If
        someone attempts to modify a frozen instance,
        :exc:`attr.exceptions.FrozenInstanceError` is raised.

        Please note:

            1. This is achieved by installing a custom ``__setattr__`` method
               on your class so you can't implement an own one.

            2. True immutability is impossible in Python.

            3. This *does* have a minor a runtime performance :ref:`impact
               <how-frozen>` when initializing new instances.  In other words:
               ``__init__`` is slightly slower with ``frozen=True``.

            4. If a class is frozen, you cannot modify ``self`` in
               ``__attrs_post_init__`` or a self-written ``__init__``. You can
               circumvent that limitation by using
               ``object.__setattr__(self, "attribute_name", value)``.

        ..  _slots: https://docs.python.org/3.5/reference/datamodel.html#slots

    ..  versionadded:: 16.0.0 *slots*
    ..  versionadded:: 16.1.0 *frozen*
    ..  versionadded:: 16.3.0 *str*, and support for ``__attrs_post_init__``.
    ..  versionchanged::
            17.1.0 *hash* supports ``None`` as value which is also the default
            now.
    """
    def wrap(cls):
        if getattr(cls, "__class__", None) is None:
            raise TypeError("attrs only works with new-style classes.")

        if repr is False and str is True:
            raise ValueError(
                "__str__ can only be generated if a __repr__ exists."
            )

        if slots:
            # Only need this later if we're using slots.
            if these is None:
                ca_list = [name
                           for name, attr
                           in cls.__dict__.items()
                           if isinstance(attr, _CountingAttr)]
            else:
                ca_list = list(iterkeys(these))
        _transform_attrs(cls, these)

        # Can't just re-use frozen name because Python's scoping. :(
        # Can't compare function objects because Python 2 is terrible. :(
        effectively_frozen = _has_frozen_superclass(cls) or frozen
        if repr is True:
            cls = _add_repr(cls, ns=repr_ns)
        if str is True:
            cls.__str__ = cls.__repr__
        if cmp is True:
            cls = _add_cmp(cls)

        if hash is not True and hash is not False and hash is not None:
            raise TypeError(
                "Invalid value for hash.  Must be True, False, or None."
            )
        elif hash is False or (hash is None and cmp is False):
            pass
        elif hash is True or (hash is None and cmp is True and frozen is True):
            cls = _add_hash(cls)
        else:
            cls.__hash__ = None

        if init is True:
            cls = _add_init(cls, effectively_frozen)
        if effectively_frozen is True:
            cls.__setattr__ = _frozen_setattrs
            cls.__delattr__ = _frozen_delattrs
            if slots is True:
                # slots and frozen require __getstate__/__setstate__ to work
                cls = _add_pickle(cls)
        if slots is True:
            cls_dict = dict(cls.__dict__)
            cls_dict["__slots__"] = tuple(ca_list)
            for ca_name in ca_list:
                # It might not actually be in there, e.g. if using 'these'.
                cls_dict.pop(ca_name, None)
            cls_dict.pop("__dict__", None)

            qualname = getattr(cls, "__qualname__", None)
            cls = type(cls)(cls.__name__, cls.__bases__, cls_dict)
            if qualname is not None:
                cls.__qualname__ = qualname

        return cls

    # attrs_or class type depends on the usage of the decorator.  It's a class
    # if it's used as `@attributes` but ``None`` if used # as `@attributes()`.
    if maybe_cls is None:
        return wrap
    else:
        return wrap(maybe_cls)


if PY2:
    def _has_frozen_superclass(cls):
        """
        Check whether *cls* has a frozen ancestor by looking at its
        __setattr__.
        """
        return (
            getattr(
                cls.__setattr__, "__module__", None
            ) == _frozen_setattrs.__module__ and
            cls.__setattr__.__name__ == _frozen_setattrs.__name__
        )
else:
    def _has_frozen_superclass(cls):
        """
        Check whether *cls* has a frozen ancestor by looking at its
        __setattr__.
        """
        return cls.__setattr__ == _frozen_setattrs


def _attrs_to_tuple(obj, attrs):
    """
    Create a tuple of all values of *obj*'s *attrs*.
    """
    return tuple(getattr(obj, a.name) for a in attrs)


def _add_hash(cls, attrs=None):
    """
    Add a hash method to *cls*.
    """
    if attrs is None:
        attrs = [a
                 for a in cls.__attrs_attrs__
                 if a.hash is True or (a.hash is None and a.cmp is True)]

    def hash_(self):
        """
        Automatically created by attrs.
        """
        return hash(_attrs_to_tuple(self, attrs))

    cls.__hash__ = hash_
    return cls


def _add_cmp(cls, attrs=None):
    """
    Add comparison methods to *cls*.
    """
    if attrs is None:
        attrs = [a for a in cls.__attrs_attrs__ if a.cmp]

    def attrs_to_tuple(obj):
        """
        Save us some typing.
        """
        return _attrs_to_tuple(obj, attrs)

    def eq(self, other):
        """
        Automatically created by attrs.
        """
        if other.__class__ is self.__class__:
            return attrs_to_tuple(self) == attrs_to_tuple(other)
        else:
            return NotImplemented

    def ne(self, other):
        """
        Automatically created by attrs.
        """
        result = eq(self, other)
        if result is NotImplemented:
            return NotImplemented
        else:
            return not result

    def lt(self, other):
        """
        Automatically created by attrs.
        """
        if isinstance(other, self.__class__):
            return attrs_to_tuple(self) < attrs_to_tuple(other)
        else:
            return NotImplemented

    def le(self, other):
        """
        Automatically created by attrs.
        """
        if isinstance(other, self.__class__):
            return attrs_to_tuple(self) <= attrs_to_tuple(other)
        else:
            return NotImplemented

    def gt(self, other):
        """
        Automatically created by attrs.
        """
        if isinstance(other, self.__class__):
            return attrs_to_tuple(self) > attrs_to_tuple(other)
        else:
            return NotImplemented

    def ge(self, other):
        """
        Automatically created by attrs.
        """
        if isinstance(other, self.__class__):
            return attrs_to_tuple(self) >= attrs_to_tuple(other)
        else:
            return NotImplemented

    cls.__eq__ = eq
    cls.__ne__ = ne
    cls.__lt__ = lt
    cls.__le__ = le
    cls.__gt__ = gt
    cls.__ge__ = ge

    return cls


def _add_repr(cls, ns=None, attrs=None):
    """
    Add a repr method to *cls*.
    """
    if attrs is None:
        attrs = [a for a in cls.__attrs_attrs__ if a.repr]

    def repr_(self):
        """
        Automatically created by attrs.
        """
        real_cls = self.__class__
        if ns is None:
            qualname = getattr(real_cls, "__qualname__", None)
            if qualname is not None:
                class_name = qualname.rsplit(">.", 1)[-1]
            else:
                class_name = real_cls.__name__
        else:
            class_name = ns + "." + real_cls.__name__

        return "{0}({1})".format(
            class_name,
            ", ".join(a.name + "=" + repr(getattr(self, a.name))
                      for a in attrs)
        )
    cls.__repr__ = repr_
    return cls


def _add_init(cls, frozen):
    """
    Add a __init__ method to *cls*.  If *frozen* is True, make it immutable.
    """
    attrs = [a for a in cls.__attrs_attrs__
             if a.init or a.default is not NOTHING]

    # We cache the generated init methods for the same kinds of attributes.
    sha1 = hashlib.sha1()
    r = repr(attrs)
    if not isinstance(r, bytes):
        r = r.encode('utf-8')
    sha1.update(r)
    unique_filename = "<attrs generated init {0}>".format(
        sha1.hexdigest()
    )

    script, globs = _attrs_to_script(
        attrs,
        frozen,
        getattr(cls, "__attrs_post_init__", False),
    )
    locs = {}
    bytecode = compile(script, unique_filename, "exec")
    attr_dict = dict((a.name, a) for a in attrs)
    globs.update({
        "NOTHING": NOTHING,
        "attr_dict": attr_dict,
    })
    if frozen is True:
        # Save the lookup overhead in __init__ if we need to circumvent
        # immutability.
        globs["_cached_setattr"] = _obj_setattr
    eval(bytecode, globs, locs)
    init = locs["__init__"]

    # In order of debuggers like PDB being able to step through the code,
    # we add a fake linecache entry.
    linecache.cache[unique_filename] = (
        len(script),
        None,
        script.splitlines(True),
        unique_filename
    )
    cls.__init__ = init
    return cls


def _add_pickle(cls):
    """
    Add pickle helpers, needed for frozen and slotted classes
    """
    def _slots_getstate__(obj):
        """
        Play nice with pickle.
        """
        return tuple(getattr(obj, a.name) for a in fields(obj.__class__))

    def _slots_setstate__(obj, state):
        """
        Play nice with pickle.
        """
        __bound_setattr = _obj_setattr.__get__(obj, Attribute)
        for a, value in zip(fields(obj.__class__), state):
            __bound_setattr(a.name, value)

    cls.__getstate__ = _slots_getstate__
    cls.__setstate__ = _slots_setstate__
    return cls


def fields(cls):
    """
    Returns the tuple of ``attrs`` attributes for a class.

    The tuple also allows accessing the fields by their names (see below for
    examples).

    :param type cls: Class to introspect.

    :raise TypeError: If *cls* is not a class.
    :raise attr.exceptions.NotAnAttrsClassError: If *cls* is not an ``attrs``
        class.

    :rtype: tuple (with name accesors) of :class:`attr.Attribute`

    ..  versionchanged:: 16.2.0 Returned tuple allows accessing the fields
        by name.
    """
    if not isclass(cls):
        raise TypeError("Passed object must be a class.")
    attrs = getattr(cls, "__attrs_attrs__", None)
    if attrs is None:
        raise NotAnAttrsClassError(
            "{cls!r} is not an attrs-decorated class.".format(cls=cls)
        )
    return attrs


def validate(inst):
    """
    Validate all attributes on *inst* that have a validator.

    Leaves all exceptions through.

    :param inst: Instance of a class with ``attrs`` attributes.
    """
    if _config._run_validators is False:
        return

    for a in fields(inst.__class__):
        v = a.validator
        if v is not None:
            v(inst, a, getattr(inst, a.name))


def _attrs_to_script(attrs, frozen, post_init):
    """
    Return a script of an initializer for *attrs* and a dict of globals.

    The globals are expected by the generated script.

     If *frozen* is True, we cannot set the attributes directly so we use
    a cached ``object.__setattr__``.
    """
    lines = []
    if frozen is True:
        lines.append(
            # Circumvent the __setattr__ descriptor to save one lookup per
            # assignment.
            "_setattr = _cached_setattr.__get__(self, self.__class__)"
        )

        def fmt_setter(attr_name, value_var):
            return "_setattr('%(attr_name)s', %(value_var)s)" % {
                "attr_name": attr_name,
                "value_var": value_var,
            }

        def fmt_setter_with_converter(attr_name, value_var):
            conv_name = _init_convert_pat.format(attr_name)
            return "_setattr('%(attr_name)s', %(conv)s(%(value_var)s))" % {
                "attr_name": attr_name,
                "value_var": value_var,
                "conv": conv_name,
            }
    else:
        def fmt_setter(attr_name, value):
            return "self.%(attr_name)s = %(value)s" % {
                "attr_name": attr_name,
                "value": value,
            }

        def fmt_setter_with_converter(attr_name, value_var):
            conv_name = _init_convert_pat.format(attr_name)
            return "self.%(attr_name)s = %(conv)s(%(value_var)s)" % {
                "attr_name": attr_name,
                "value_var": value_var,
                "conv": conv_name,
            }

    args = []
    attrs_to_validate = []

    # This is a dictionary of names to validator and converter callables.
    # Injecting this into __init__ globals lets us avoid lookups.
    names_for_globals = {}

    for a in attrs:
        if a.validator:
            attrs_to_validate.append(a)
        attr_name = a.name
        arg_name = a.name.lstrip("_")
        has_factory = isinstance(a.default, Factory)
        if has_factory and a.default.takes_self:
            maybe_self = "self"
        else:
            maybe_self = ""
        if a.init is False:
            if has_factory:
                init_factory_name = _init_factory_pat.format(a.name)
                if a.convert is not None:
                    lines.append(fmt_setter_with_converter(
                        attr_name,
                        init_factory_name + "({0})".format(maybe_self)))
                    conv_name = _init_convert_pat.format(a.name)
                    names_for_globals[conv_name] = a.convert
                else:
                    lines.append(fmt_setter(
                        attr_name,
                        init_factory_name + "({0})".format(maybe_self)
                    ))
                names_for_globals[init_factory_name] = a.default.factory
            else:
                if a.convert is not None:
                    lines.append(fmt_setter_with_converter(
                        attr_name,
                        "attr_dict['{attr_name}'].default"
                        .format(attr_name=attr_name)
                    ))
                    conv_name = _init_convert_pat.format(a.name)
                    names_for_globals[conv_name] = a.convert
                else:
                    lines.append(fmt_setter(
                        attr_name,
                        "attr_dict['{attr_name}'].default"
                        .format(attr_name=attr_name)
                    ))
        elif a.default is not NOTHING and not has_factory:
            args.append(
                "{arg_name}=attr_dict['{attr_name}'].default".format(
                    arg_name=arg_name,
                    attr_name=attr_name,
                )
            )
            if a.convert is not None:
                lines.append(fmt_setter_with_converter(attr_name, arg_name))
                names_for_globals[_init_convert_pat.format(a.name)] = a.convert
            else:
                lines.append(fmt_setter(attr_name, arg_name))
        elif has_factory:
            args.append("{arg_name}=NOTHING".format(arg_name=arg_name))
            lines.append("if {arg_name} is not NOTHING:"
                         .format(arg_name=arg_name))
            init_factory_name = _init_factory_pat.format(a.name)
            if a.convert is not None:
                lines.append("    " + fmt_setter_with_converter(attr_name,
                                                                arg_name))
                lines.append("else:")
                lines.append("    " + fmt_setter_with_converter(
                    attr_name,
                    init_factory_name + "({0})".format(maybe_self)
                ))
                names_for_globals[_init_convert_pat.format(a.name)] = a.convert
            else:
                lines.append("    " + fmt_setter(attr_name, arg_name))
                lines.append("else:")
                lines.append("    " + fmt_setter(
                    attr_name,
                    init_factory_name + "({0})".format(maybe_self)
                ))
            names_for_globals[init_factory_name] = a.default.factory
        else:
            args.append(arg_name)
            if a.convert is not None:
                lines.append(fmt_setter_with_converter(attr_name, arg_name))
                names_for_globals[_init_convert_pat.format(a.name)] = a.convert
            else:
                lines.append(fmt_setter(attr_name, arg_name))

    if attrs_to_validate:  # we can skip this if there are no validators.
        names_for_globals["_config"] = _config
        lines.append("if _config._run_validators is True:")
        for a in attrs_to_validate:
            val_name = "__attr_validator_{}".format(a.name)
            attr_name = "__attr_{}".format(a.name)
            lines.append("    {}(self, {}, self.{})".format(
                val_name, attr_name, a.name))
            names_for_globals[val_name] = a.validator
            names_for_globals[attr_name] = a
    if post_init:
        lines.append("self.__attrs_post_init__()")

    return """\
def __init__(self, {args}):
    {lines}
""".format(
        args=", ".join(args),
        lines="\n    ".join(lines) if lines else "pass",
    ), names_for_globals


class Attribute(object):
    """
    *Read-only* representation of an attribute.

    :attribute name: The name of the attribute.

    Plus *all* arguments of :func:`attr.ib`.
    """
    __slots__ = (
        "name", "default", "validator", "repr", "cmp", "hash", "init",
        "convert", "metadata",
    )

    def __init__(self, name, default, validator, repr, cmp, hash, init,
                 convert=None, metadata=None):
        # Cache this descriptor here to speed things up later.
        bound_setattr = _obj_setattr.__get__(self, Attribute)

        bound_setattr("name", name)
        bound_setattr("default", default)
        bound_setattr("validator", validator)
        bound_setattr("repr", repr)
        bound_setattr("cmp", cmp)
        bound_setattr("hash", hash)
        bound_setattr("init", init)
        bound_setattr("convert", convert)
        bound_setattr("metadata", (metadata_proxy(metadata) if metadata
                                   else _empty_metadata_singleton))

    def __setattr__(self, name, value):
        raise FrozenInstanceError()

    @classmethod
    def from_counting_attr(cls, name, ca):
        inst_dict = {
            k: getattr(ca, k)
            for k
            in Attribute.__slots__
            if k not in (
                "name", "validator", "default",
            )  # exclude methods
        }
        return cls(name=name, validator=ca._validator, default=ca._default,
                   **inst_dict)

    # Don't use _add_pickle since fields(Attribute) doesn't work
    def __getstate__(self):
        """
        Play nice with pickle.
        """
        return tuple(getattr(self, name) if name != "metadata"
                     else dict(self.metadata)
                     for name in self.__slots__)

    def __setstate__(self, state):
        """
        Play nice with pickle.
        """
        bound_setattr = _obj_setattr.__get__(self, Attribute)
        for name, value in zip(self.__slots__, state):
            if name != "metadata":
                bound_setattr(name, value)
            else:
                bound_setattr(name, metadata_proxy(value) if value else
                              _empty_metadata_singleton)


_a = [Attribute(name=name, default=NOTHING, validator=None,
                repr=True, cmp=True, hash=(name != "metadata"), init=True)
      for name in Attribute.__slots__]

Attribute = _add_hash(
    _add_cmp(_add_repr(Attribute, attrs=_a), attrs=_a),
    attrs=[a for a in _a if a.hash]
)


class _CountingAttr(object):
    """
    Intermediate representation of attributes that uses a counter to preserve
    the order in which the attributes have been defined.

    *Internal* data structure of the attrs library.  Running into is most
    likely the result of a bug like a forgotten `@attr.s` decorator.
    """
    __slots__ = ("counter", "_default", "repr", "cmp", "hash", "init",
                 "metadata", "_validator", "convert")
    __attrs_attrs__ = tuple(
        Attribute(name=name, default=NOTHING, validator=None,
                  repr=True, cmp=True, hash=True, init=True)
        for name
        in ("counter", "_default", "repr", "cmp", "hash", "init",)
    ) + (
        Attribute(name="metadata", default=None, validator=None,
                  repr=True, cmp=True, hash=False, init=True),
    )
    cls_counter = 0

    def __init__(self, default, validator, repr, cmp, hash, init, convert,
                 metadata):
        _CountingAttr.cls_counter += 1
        self.counter = _CountingAttr.cls_counter
        self._default = default
        # If validator is a list/tuple, wrap it using helper validator.
        if validator and isinstance(validator, (list, tuple)):
            self._validator = and_(*validator)
        else:
            self._validator = validator
        self.repr = repr
        self.cmp = cmp
        self.hash = hash
        self.init = init
        self.convert = convert
        self.metadata = metadata

    def validator(self, meth):
        """
        Decorator that adds *meth* to the list of validators.

        Returns *meth* unchanged.

        .. versionadded:: 17.1.0
        """
        if self._validator is None:
            self._validator = meth
        else:
            self._validator = and_(self._validator, meth)
        return meth

    def default(self, meth):
        """
        Decorator that allows to set the default for an attribute.

        Returns *meth* unchanged.

        :raises DefaultAlreadySetError: If default has been set before.

        .. versionadded:: 17.1.0
        """
        if self._default is not NOTHING:
            raise DefaultAlreadySetError()

        self._default = Factory(meth, takes_self=True)

        return meth


_CountingAttr = _add_cmp(_add_repr(_CountingAttr))


@attributes(slots=True, init=False)
class Factory(object):
    """
    Stores a factory callable.

    If passed as the default value to :func:`attr.ib`, the factory is used to
    generate a new value.

    :param callable factory: A callable that takes either none or exactly one
        mandatory positional argument depending on *takes_self*.
    :param bool takes_self: Pass the partially initialized instance that is
        being initialized as a positional argument.

    .. versionadded:: 17.1.0  *takes_self*
    """
    factory = attr()
    takes_self = attr()

    def __init__(self, factory, takes_self=False):
        """
        `Factory` is part of the default machinery so if we want a default
        value here, we have to implement it ourselves.
        """
        self.factory = factory
        self.takes_self = takes_self


def make_class(name, attrs, bases=(object,), **attributes_arguments):
    """
    A quick way to create a new class called *name* with *attrs*.

    :param name: The name for the new class.
    :type name: str

    :param attrs: A list of names or a dictionary of mappings of names to
        attributes.
    :type attrs: :class:`list` or :class:`dict`

    :param tuple bases: Classes that the new class will subclass.

    :param attributes_arguments: Passed unmodified to :func:`attr.s`.

    :return: A new class with *attrs*.
    :rtype: type

    ..  versionadded:: 17.1.0 *bases*
    """
    if isinstance(attrs, dict):
        cls_dict = attrs
    elif isinstance(attrs, (list, tuple)):
        cls_dict = dict((a, attr()) for a in attrs)
    else:
        raise TypeError("attrs argument must be a dict or a list.")

    return attributes(**attributes_arguments)(type(name, bases, cls_dict))


# These are required by whithin this module so we define them here and merely
# import into .validators.


@attributes(slots=True, hash=True)
class _AndValidator(object):
    """
    Compose many validators to a single one.
    """
    _validators = attr()

    def __call__(self, inst, attr, value):
        for v in self._validators:
            v(inst, attr, value)


def and_(*validators):
    """
    A validator that composes multiple validators into one.

    When called on a value, it runs all wrapped validators.

    :param validators: Arbitrary number of validators.
    :type validators: callables

    .. versionadded:: 17.1.0
    """
    vals = []
    for validator in validators:
        vals.extend(
            validator._validators if isinstance(validator, _AndValidator)
            else [validator]
        )

    return _AndValidator(tuple(vals))