_make

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

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

    :param callables validators: Arbitrary number of validators.

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

    return _AndValidator(tuple(vals))

def attrib(
    default=NOTHING,
    validator=None,
    repr=True,
    cmp=None,
    hash=None,
    init=True,
    metadata=None,
    type=None,
    converter=None,
    factory=None,
    kw_only=False,
    eq=None,
    order=None,
    on_setattr=None,
):
    """
    Create a new attribute on a class.

    ..  warning::

        Does *not* do anything unless the class is also decorated with
        `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 `Factory`, its callable will be
        used to construct a new value (useful for mutable data types 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 `TypeError`
        will be raised.

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

    :type default: Any value

    :param callable factory: Syntactic sugar for
        ``default=attr.Factory(factory)``.

    :param validator: `callable` that is called by ``attrs``-generated
        ``__init__`` methods after the instance has been initialized.  They
        receive the initialized instance, the `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
        `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 repr: Include this attribute in the generated ``__repr__``
        method. If ``True``, include the attribute; if ``False``, omit it. By
        default, the built-in ``repr()`` function is used. To override how the
        attribute value is formatted, pass a ``callable`` that takes a single
        value and returns a string. Note that the resulting string is used
        as-is, i.e. it will be used directly *instead* of calling ``repr()``
        (the default).
    :type repr: a `bool` or a `callable` to use a custom function.

    :param eq: If ``True`` (default), include this attribute in the
        generated ``__eq__`` and ``__ne__`` methods that check two instances
        for equality. To override how the attribute value is compared,
        pass a ``callable`` that takes a single value and returns the value
        to be compared.
    :type eq: a `bool` or a `callable`.

    :param order: If ``True`` (default), include this attributes in the
        generated ``__lt__``, ``__le__``, ``__gt__`` and ``__ge__`` methods.
        To override how the attribute value is ordered,
        pass a ``callable`` that takes a single value and returns the value
        to be ordered.
    :type order: a `bool` or a `callable`.

    :param cmp: Setting *cmp* is equivalent to setting *eq* and *order* to the
        same value. Must not be mixed with *eq* or *order*.
    :type cmp: a `bool` or a `callable`.

    :param Optional[bool] hash: Include this attribute in the generated
        ``__hash__`` method.  If ``None`` (default), mirror *eq*'s value.  This
        is the correct behavior according the Python spec.  Setting this value
        to anything else than ``None`` is *discouraged*.
    :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 converter: `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 `extending_metadata`.
    :param type: The type of the attribute.  In Python 3.6 or greater, the
        preferred method to specify the type is using a variable annotation
        (see `PEP 526 <https://www.python.org/dev/peps/pep-0526/>`_).
        This argument is provided for backward compatibility.
        Regardless of the approach used, the type will be stored on
        ``Attribute.type``.

        Please note that ``attrs`` doesn't do anything with this metadata by
        itself. You can use it as part of your own code or for
        `static type checking <types>`.
    :param kw_only: Make this attribute keyword-only (Python 3+)
        in the generated ``__init__`` (if ``init`` is ``False``, this
        parameter is ignored).
    :param on_setattr: Allows to overwrite the *on_setattr* setting from
        `attr.s`. If left `None`, the *on_setattr* value from `attr.s` is used.
        Set to `attr.setters.NO_OP` to run **no** `setattr` hooks for this
        attribute -- regardless of the setting in `attr.s`.
    :type on_setattr: `callable`, or a list of callables, or `None`, or
        `attr.setters.NO_OP`

    .. versionadded:: 15.2.0 *convert*
    .. versionadded:: 16.3.0 *metadata*
    .. versionchanged:: 17.1.0 *validator* can be a ``list`` now.
    .. versionchanged:: 17.1.0
       *hash* is ``None`` and therefore mirrors *eq* by default.
    .. versionadded:: 17.3.0 *type*
    .. deprecated:: 17.4.0 *convert*
    .. versionadded:: 17.4.0 *converter* as a replacement for the deprecated
       *convert* to achieve consistency with other noun-based arguments.
    .. versionadded:: 18.1.0
       ``factory=f`` is syntactic sugar for ``default=attr.Factory(f)``.
    .. versionadded:: 18.2.0 *kw_only*
    .. versionchanged:: 19.2.0 *convert* keyword argument removed.
    .. versionchanged:: 19.2.0 *repr* also accepts a custom callable.
    .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01.
    .. versionadded:: 19.2.0 *eq* and *order*
    .. versionadded:: 20.1.0 *on_setattr*
    .. versionchanged:: 20.3.0 *kw_only* backported to Python 2
    .. versionchanged:: 21.1.0
       *eq*, *order*, and *cmp* also accept a custom callable
    .. versionchanged:: 21.1.0 *cmp* undeprecated
    """
    eq, eq_key, order, order_key = _determine_attrib_eq_order(
        cmp, eq, order, True
    )

    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."
        )

    if factory is not None:
        if default is not NOTHING:
            raise ValueError(
                "The `default` and `factory` arguments are mutually "
                "exclusive."
            )
        if not callable(factory):
            raise ValueError("The `factory` argument must be a callable.")
        default = Factory(factory)

    if metadata is None:
        metadata = {}

    # Apply syntactic sugar by auto-wrapping.
    if isinstance(on_setattr, (list, tuple)):
        on_setattr = setters.pipe(*on_setattr)

    if validator and isinstance(validator, (list, tuple)):
        validator = and_(*validator)

    if converter and isinstance(converter, (list, tuple)):
        converter = pipe(*converter)

    return _CountingAttr(
        default=default,
        validator=validator,
        repr=repr,
        cmp=None,
        hash=hash,
        init=init,
        converter=converter,
        metadata=metadata,
        type=type,
        kw_only=kw_only,
        eq=eq,
        eq_key=eq_key,
        order=order,
        order_key=order_key,
        on_setattr=on_setattr,
    )

def attrs(
    maybe_cls=None,
    these=None,
    repr_ns=None,
    repr=None,
    cmp=None,
    hash=None,
    init=None,
    slots=False,
    frozen=False,
    weakref_slot=True,
    str=False,
    auto_attribs=False,
    kw_only=False,
    cache_hash=False,
    auto_exc=False,
    eq=None,
    order=None,
    auto_detect=False,
    collect_by_mro=False,
    getstate_setstate=None,
    on_setattr=None,
    field_transformer=None,
):
    r"""
    A class decorator that adds `dunder
    <https://wiki.python.org/moin/DunderAlias>`_\ -methods according to the
    specified attributes using `attr.ib` or the *these* argument.

    :param these: A dictionary of name to `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 and will *not* remove any attributes from it.

        If *these* is an ordered dict (`dict` on Python 3.6+,
        `collections.OrderedDict` otherwise), the order is deduced from
        the order of the attributes inside *these*.  Otherwise the order
        of the definition of the attributes is used.

    :type these: `dict` of `str` to `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 auto_detect: Instead of setting the *init*, *repr*, *eq*,
        *order*, and *hash* arguments explicitly, assume they are set to
        ``True`` **unless any** of the involved methods for one of the
        arguments is implemented in the *current* class (i.e. it is *not*
        inherited from some base class).

        So for example by implementing ``__eq__`` on a class yourself,
        ``attrs`` will deduce ``eq=False`` and will create *neither*
        ``__eq__`` *nor* ``__ne__`` (but Python classes come with a sensible
        ``__ne__`` by default, so it *should* be enough to only implement
        ``__eq__`` in most cases).

        .. warning::

           If you prevent ``attrs`` from creating the ordering methods for you
           (``order=False``, e.g. by implementing ``__le__``), it becomes
           *your* responsibility to make sure its ordering is sound. The best
           way is to use the `functools.total_ordering` decorator.


        Passing ``True`` or ``False`` to *init*, *repr*, *eq*, *order*,
        *cmp*, or *hash* overrides whatever *auto_detect* would determine.

        *auto_detect* requires Python 3. Setting it ``True`` on Python 2 raises
        a `PythonTooOldError`.

    :param bool repr: Create a ``__repr__`` method with a human readable
        representation of ``attrs`` attributes..
    :param bool str: Create a ``__str__`` method that is identical to
        ``__repr__``.  This is usually not necessary except for
        `Exception`\ s.
    :param Optional[bool] eq: If ``True`` or ``None`` (default), add ``__eq__``
        and ``__ne__`` methods that check two instances for equality.

        They compare the instances as if they were tuples of their ``attrs``
        attributes if and only if the types of both classes are *identical*!
    :param Optional[bool] order: If ``True``, add ``__lt__``, ``__le__``,
        ``__gt__``, and ``__ge__`` methods that behave like *eq* above and
        allow instances to be ordered. If ``None`` (default) mirror value of
        *eq*.
    :param Optional[bool] cmp: Setting *cmp* is equivalent to setting *eq*
        and *order* to the same value. Must not be mixed with *eq* or *order*.
    :param Optional[bool] hash: If ``None`` (default), the ``__hash__`` method
        is generated according how *eq* and *frozen* are set.

        1. If *both* are True, ``attrs`` will generate a ``__hash__`` for you.
        2. If *eq* is True and *frozen* is False, ``__hash__`` will be set to
           None, marking it unhashable (which it is).
        3. If *eq* is False, ``__hash__`` will be left untouched meaning the
           ``__hash__`` method of the base class will be used (if base class 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 our documentation on `hashing`, Python's documentation on
        `object.__hash__`, and the `GitHub issue that led to the default \
        behavior <https://github.com/python-attrs/attrs/issues/136>`_ for more
        details.
    :param bool init: Create a ``__init__`` method that initializes the
        ``attrs`` attributes. Leading underscores are stripped for the argument
        name. If a ``__attrs_pre_init__`` method exists on the class, it will
        be called before the class is initialized. If a ``__attrs_post_init__``
        method exists on the class, it will be called after the class is fully
        initialized.

        If ``init`` is ``False``, an ``__attrs_init__`` method will be
        injected instead. This allows you to define a custom ``__init__``
        method that can do pre-init work such as ``super().__init__()``,
        and then call ``__attrs_init__()`` and ``__attrs_post_init__()``.
    :param bool slots: Create a `slotted class <slotted classes>` that's more
        memory-efficient. Slotted classes are generally superior to the default
        dict classes, but have some gotchas you should know about, so we
        encourage you to read the `glossary entry <slotted classes>`.
    :param bool frozen: Make instances immutable after initialization.  If
        someone attempts to modify a frozen instance,
        `attr.exceptions.FrozenInstanceError` is raised.

        .. note::

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

            2. True immutability is impossible in Python.

            3. This *does* have a minor a runtime performance `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)``.

            5. Subclasses of a frozen class are frozen too.

    :param bool weakref_slot: Make instances weak-referenceable.  This has no
        effect unless ``slots`` is also enabled.
    :param bool auto_attribs: If ``True``, collect `PEP 526`_-annotated
        attributes (Python 3.6 and later only) from the class body.

        In this case, you **must** annotate every field.  If ``attrs``
        encounters a field that is set to an `attr.ib` but lacks a type
        annotation, an `attr.exceptions.UnannotatedAttributeError` is
        raised.  Use ``field_name: typing.Any = attr.ib(...)`` if you don't
        want to set a type.

        If you assign a value to those attributes (e.g. ``x: int = 42``), that
        value becomes the default value like if it were passed using
        ``attr.ib(default=42)``.  Passing an instance of `Factory` also
        works as expected in most cases (see warning below).

        Attributes annotated as `typing.ClassVar`, and attributes that are
        neither annotated nor set to an `attr.ib` are **ignored**.

        .. warning::
           For features that use the attribute name to create decorators (e.g.
           `validators <validators>`), you still *must* assign `attr.ib` to
           them. Otherwise Python will either not find the name or try to use
           the default value to call e.g. ``validator`` on it.

           These errors can be quite confusing and probably the most common bug
           report on our bug tracker.

        .. _`PEP 526`: https://www.python.org/dev/peps/pep-0526/
    :param bool kw_only: Make all attributes keyword-only (Python 3+)
        in the generated ``__init__`` (if ``init`` is ``False``, this
        parameter is ignored).
    :param bool cache_hash: Ensure that the object's hash code is computed
        only once and stored on the object.  If this is set to ``True``,
        hashing must be either explicitly or implicitly enabled for this
        class.  If the hash code is cached, avoid any reassignments of
        fields involved in hash code computation or mutations of the objects
        those fields point to after object creation.  If such changes occur,
        the behavior of the object's hash code is undefined.
    :param bool auto_exc: If the class subclasses `BaseException`
        (which implicitly includes any subclass of any exception), the
        following happens to behave like a well-behaved Python exceptions
        class:

        - the values for *eq*, *order*, and *hash* are ignored and the
          instances compare and hash by the instance's ids (N.B. ``attrs`` will
          *not* remove existing implementations of ``__hash__`` or the equality
          methods. It just won't add own ones.),
        - all attributes that are either passed into ``__init__`` or have a
          default value are additionally available as a tuple in the ``args``
          attribute,
        - the value of *str* is ignored leaving ``__str__`` to base classes.
    :param bool collect_by_mro: Setting this to `True` fixes the way ``attrs``
       collects attributes from base classes.  The default behavior is
       incorrect in certain cases of multiple inheritance.  It should be on by
       default but is kept off for backward-compatability.

       See issue `#428 <https://github.com/python-attrs/attrs/issues/428>`_ for
       more details.

    :param Optional[bool] getstate_setstate:
       .. note::
          This is usually only interesting for slotted classes and you should
          probably just set *auto_detect* to `True`.

       If `True`, ``__getstate__`` and
       ``__setstate__`` are generated and attached to the class. This is
       necessary for slotted classes to be pickleable. If left `None`, it's
       `True` by default for slotted classes and ``False`` for dict classes.

       If *auto_detect* is `True`, and *getstate_setstate* is left `None`,
       and **either** ``__getstate__`` or ``__setstate__`` is detected directly
       on the class (i.e. not inherited), it is set to `False` (this is usually
       what you want).

    :param on_setattr: A callable that is run whenever the user attempts to set
        an attribute (either by assignment like ``i.x = 42`` or by using
        `setattr` like ``setattr(i, "x", 42)``). It receives the same arguments
        as validators: the instance, the attribute that is being modified, and
        the new value.

        If no exception is raised, the attribute is set to the return value of
        the callable.

        If a list of callables is passed, they're automatically wrapped in an
        `attr.setters.pipe`.

    :param Optional[callable] field_transformer:
        A function that is called with the original class object and all
        fields right before ``attrs`` finalizes the class.  You can use
        this, e.g., to automatically add converters or validators to
        fields based on their types.  See `transform-fields` for more details.

    .. versionadded:: 16.0.0 *slots*
    .. versionadded:: 16.1.0 *frozen*
    .. versionadded:: 16.3.0 *str*
    .. versionadded:: 16.3.0 Support for ``__attrs_post_init__``.
    .. versionchanged:: 17.1.0
       *hash* supports ``None`` as value which is also the default now.
    .. versionadded:: 17.3.0 *auto_attribs*
    .. versionchanged:: 18.1.0
       If *these* is passed, no attributes are deleted from the class body.
    .. versionchanged:: 18.1.0 If *these* is ordered, the order is retained.
    .. versionadded:: 18.2.0 *weakref_slot*
    .. deprecated:: 18.2.0
       ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now raise a
       `DeprecationWarning` if the classes compared are subclasses of
       each other. ``__eq`` and ``__ne__`` never tried to compared subclasses
       to each other.
    .. versionchanged:: 19.2.0
       ``__lt__``, ``__le__``, ``__gt__``, and ``__ge__`` now do not consider
       subclasses comparable anymore.
    .. versionadded:: 18.2.0 *kw_only*
    .. versionadded:: 18.2.0 *cache_hash*
    .. versionadded:: 19.1.0 *auto_exc*
    .. deprecated:: 19.2.0 *cmp* Removal on or after 2021-06-01.
    .. versionadded:: 19.2.0 *eq* and *order*
    .. versionadded:: 20.1.0 *auto_detect*
    .. versionadded:: 20.1.0 *collect_by_mro*
    .. versionadded:: 20.1.0 *getstate_setstate*
    .. versionadded:: 20.1.0 *on_setattr*
    .. versionadded:: 20.3.0 *field_transformer*
    .. versionchanged:: 21.1.0
       ``init=False`` injects ``__attrs_init__``
    .. versionchanged:: 21.1.0 Support for ``__attrs_pre_init__``
    .. versionchanged:: 21.1.0 *cmp* undeprecated
    """
    if auto_detect and PY2:
        raise PythonTooOldError(
            "auto_detect only works on Python 3 and later."
        )

    eq_, order_ = _determine_attrs_eq_order(cmp, eq, order, None)
    hash_ = hash  # work around the lack of nonlocal

    if isinstance(on_setattr, (list, tuple)):
        on_setattr = setters.pipe(*on_setattr)

    def wrap(cls):

        if getattr(cls, "__class__", None) is None:
            raise TypeError("attrs only works with new-style classes.")

        is_frozen = frozen or _has_frozen_base_class(cls)
        is_exc = auto_exc is True and issubclass(cls, BaseException)
        has_own_setattr = auto_detect and _has_own_attribute(
            cls, "__setattr__"
        )

        if has_own_setattr and is_frozen:
            raise ValueError("Can't freeze a class with a custom __setattr__.")

        builder = _ClassBuilder(
            cls,
            these,
            slots,
            is_frozen,
            weakref_slot,
            _determine_whether_to_implement(
                cls,
                getstate_setstate,
                auto_detect,
                ("__getstate__", "__setstate__"),
                default=slots,
            ),
            auto_attribs,
            kw_only,
            cache_hash,
            is_exc,
            collect_by_mro,
            on_setattr,
            has_own_setattr,
            field_transformer,
        )
        if _determine_whether_to_implement(
            cls, repr, auto_detect, ("__repr__",)
        ):
            builder.add_repr(repr_ns)
        if str is True:
            builder.add_str()

        eq = _determine_whether_to_implement(
            cls, eq_, auto_detect, ("__eq__", "__ne__")
        )
        if not is_exc and eq is True:
            builder.add_eq()
        if not is_exc and _determine_whether_to_implement(
            cls, order_, auto_detect, ("__lt__", "__le__", "__gt__", "__ge__")
        ):
            builder.add_order()

        builder.add_setattr()

        if (
            hash_ is None
            and auto_detect is True
            and _has_own_attribute(cls, "__hash__")
        ):
            hash = False
        else:
            hash = hash_
        if hash is not True and hash is not False and hash is not None:
            # Can't use `hash in` because 1 == True for example.
            raise TypeError(
                "Invalid value for hash.  Must be True, False, or None."
            )
        elif hash is False or (hash is None and eq is False) or is_exc:
            # Don't do anything. Should fall back to __object__'s __hash__
            # which is by id.
            if cache_hash:
                raise TypeError(
                    "Invalid value for cache_hash.  To use hash caching,"
                    " hashing must be either explicitly or implicitly "
                    "enabled."
                )
        elif hash is True or (
            hash is None and eq is True and is_frozen is True
        ):
            # Build a __hash__ if told so, or if it's safe.
            builder.add_hash()
        else:
            # Raise TypeError on attempts to hash.
            if cache_hash:
                raise TypeError(
                    "Invalid value for cache_hash.  To use hash caching,"
                    " hashing must be either explicitly or implicitly "
                    "enabled."
                )
            builder.make_unhashable()

        if _determine_whether_to_implement(
            cls, init, auto_detect, ("__init__",)
        ):
            builder.add_init()
        else:
            builder.add_attrs_init()
            if cache_hash:
                raise TypeError(
                    "Invalid value for cache_hash.  To use hash caching,"
                    " init must be True."
                )

        return builder.build_class()

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

def fields(cls):
    """
    Return 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 accessors) of `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 fields_dict(cls):
    """
    Return an ordered dictionary of ``attrs`` attributes for a class, whose
    keys are the attribute names.

    :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: an ordered dict where keys are attribute names and values are
        `attr.Attribute`\\ s. This will be a `dict` if it's
        naturally ordered like on Python 3.6+ or an
        :class:`~collections.OrderedDict` otherwise.

    .. versionadded:: 18.1.0
    """
    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 ordered_dict(((a.name, a) for a in attrs))

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

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

    :param attrs: A list of names or a dictionary of mappings of names to
        attributes.

        If *attrs* is a list or an ordered dict (`dict` on Python 3.6+,
        `collections.OrderedDict` otherwise), the order is deduced from
        the order of the names or attributes inside *attrs*.  Otherwise the
        order of the definition of the attributes is used.
    :type attrs: `list` or `dict`

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

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

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

    .. versionadded:: 17.1.0 *bases*
    .. versionchanged:: 18.1.0 If *attrs* is ordered, the order is retained.
    """
    if isinstance(attrs, dict):
        cls_dict = attrs
    elif isinstance(attrs, (list, tuple)):
        cls_dict = dict((a, attrib()) for a in attrs)
    else:
        raise TypeError("attrs argument must be a dict or a list.")

    pre_init = cls_dict.pop("__attrs_pre_init__", None)
    post_init = cls_dict.pop("__attrs_post_init__", None)
    user_init = cls_dict.pop("__init__", None)

    body = {}
    if pre_init is not None:
        body["__attrs_pre_init__"] = pre_init
    if post_init is not None:
        body["__attrs_post_init__"] = post_init
    if user_init is not None:
        body["__init__"] = user_init

    type_ = new_class(name, bases, {}, lambda ns: ns.update(body))

    # For pickling to work, the __module__ variable needs to be set to the
    # frame where the class is created.  Bypass this step in environments where
    # sys._getframe is not defined (Jython for example) or sys._getframe is not
    # defined for arguments greater than 0 (IronPython).
    try:
        type_.__module__ = sys._getframe(1).f_globals.get(
            "__name__", "__main__"
        )
    except (AttributeError, ValueError):
        pass

    # We do it here for proper warnings with meaningful stacklevel.
    cmp = attributes_arguments.pop("cmp", None)
    (
        attributes_arguments["eq"],
        attributes_arguments["order"],
    ) = _determine_attrs_eq_order(
        cmp,
        attributes_arguments.get("eq"),
        attributes_arguments.get("order"),
        True,
    )

    return _attrs(these=cls_dict, **attributes_arguments)(type_)

def pipe(*converters):
    """
    A converter that composes multiple converters into one.

    When called on a value, it runs all wrapped converters, returning the
    *last* value.

    Type annotations will be inferred from the wrapped converters', if
    they have any.

    :param callables converters: Arbitrary number of converters.

    .. versionadded:: 20.1.0
    """

    def pipe_converter(val):
        for converter in converters:
            val = converter(val)

        return val

    if not PY2:
        if not converters:
            # If the converter list is empty, pipe_converter is the identity.
            A = typing.TypeVar("A")
            pipe_converter.__annotations__ = {"val": A, "return": A}
        else:
            # Get parameter type.
            sig = None
            try:
                sig = inspect.signature(converters[0])
            except (ValueError, TypeError):  # inspect failed
                pass
            if sig:
                params = list(sig.parameters.values())
                if (
                    params
                    and params[0].annotation is not inspect.Parameter.empty
                ):
                    pipe_converter.__annotations__["val"] = params[
                        0
                    ].annotation
            # Get return type.
            sig = None
            try:
                sig = inspect.signature(converters[-1])
            except (ValueError, TypeError):  # inspect failed
                pass
            if sig and sig.return_annotation is not inspect.Signature().empty:
                pipe_converter.__annotations__[
                    "return"
                ] = sig.return_annotation

    return pipe_converter

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))