Add m-esr52 at 52.6.0

1 files changed, 1954 insertions, 0 deletions

diff --git a/python/voluptuous/voluptuous.py b/python/voluptuous/voluptuous.py
new file mode 100644
index 000000000..132c3c476
--- /dev/null
+++ b/python/voluptuous/voluptuous.py
@@ -0,0 +1,1954 @@
+# encoding: utf-8
+#
+# Copyright (C) 2010-2013 Alec Thomas <alec@swapoff.org>
+# All rights reserved.
+#
+# This software is licensed as described in the file COPYING, which
+# you should have received as part of this distribution.
+#
+# Author: Alec Thomas <alec@swapoff.org>
+
+"""Schema validation for Python data structures.
+
+Given eg. a nested data structure like this:
+
+    {
+        'exclude': ['Users', 'Uptime'],
+        'include': [],
+        'set': {
+            'snmp_community': 'public',
+            'snmp_timeout': 15,
+            'snmp_version': '2c',
+        },
+        'targets': {
+            'localhost': {
+                'exclude': ['Uptime'],
+                'features': {
+                    'Uptime': {
+                        'retries': 3,
+                    },
+                    'Users': {
+                        'snmp_community': 'monkey',
+                        'snmp_port': 15,
+                    },
+                },
+                'include': ['Users'],
+                'set': {
+                    'snmp_community': 'monkeys',
+                },
+            },
+        },
+    }
+
+A schema like this:
+
+    >>> settings = {
+    ...   'snmp_community': str,
+    ...   'retries': int,
+    ...   'snmp_version': All(Coerce(str), Any('3', '2c', '1')),
+    ... }
+    >>> features = ['Ping', 'Uptime', 'Http']
+    >>> schema = Schema({
+    ...    'exclude': features,
+    ...    'include': features,
+    ...    'set': settings,
+    ...    'targets': {
+    ...      'exclude': features,
+    ...      'include': features,
+    ...      'features': {
+    ...        str: settings,
+    ...      },
+    ...    },
+    ... })
+
+Validate like so:
+
+    >>> schema({
+    ...   'set': {
+    ...     'snmp_community': 'public',
+    ...     'snmp_version': '2c',
+    ...   },
+    ...   'targets': {
+    ...     'exclude': ['Ping'],
+    ...     'features': {
+    ...       'Uptime': {'retries': 3},
+    ...       'Users': {'snmp_community': 'monkey'},
+    ...     },
+    ...   },
+    ... }) == {
+    ...   'set': {'snmp_version': '2c', 'snmp_community': 'public'},
+    ...   'targets': {
+    ...     'exclude': ['Ping'],
+    ...     'features': {'Uptime': {'retries': 3},
+    ...                  'Users': {'snmp_community': 'monkey'}}}}
+    True
+"""
+import collections
+import datetime
+import inspect
+import os
+import re
+import sys
+from contextlib import contextmanager
+from functools import wraps
+
+
+if sys.version_info >= (3,):
+    import urllib.parse as urlparse
+    long = int
+    unicode = str
+    basestring = str
+    ifilter = filter
+    iteritems = lambda d: d.items()
+else:
+    from itertools import ifilter
+    import urlparse
+    iteritems = lambda d: d.iteritems()
+
+
+__author__ = 'Alec Thomas <alec@swapoff.org>'
+__version__ = '0.8.11'
+
+
+@contextmanager
+def raises(exc, msg=None, regex=None):
+    try:
+        yield
+    except exc as e:
+        if msg is not None:
+            assert str(e) == msg, '%r != %r' % (str(e), msg)
+        if regex is not None:
+            assert re.search(regex, str(e)), '%r does not match %r' % (str(e), regex)
+
+
+class Undefined(object):
+    def __nonzero__(self):
+        return False
+
+    def __repr__(self):
+        return '...'
+
+
+UNDEFINED = Undefined()
+
+
+def default_factory(value):
+    if value is UNDEFINED or callable(value):
+        return value
+    return lambda: value
+
+
+# options for extra keys
+PREVENT_EXTRA = 0  # any extra key not in schema will raise an error
+ALLOW_EXTRA = 1    # extra keys not in schema will be included in output
+REMOVE_EXTRA = 2   # extra keys not in schema will be excluded from output
+
+
+class Error(Exception):
+    """Base validation exception."""
+
+
+class SchemaError(Error):
+    """An error was encountered in the schema."""
+
+
+class Invalid(Error):
+    """The data was invalid.
+
+    :attr msg: The error message.
+    :attr path: The path to the error, as a list of keys in the source data.
+    :attr error_message: The actual error message that was raised, as a
+        string.
+
+    """
+
+    def __init__(self, message, path=None, error_message=None, error_type=None):
+        Error.__init__(self, message)
+        self.path = path or []
+        self.error_message = error_message or message
+        self.error_type = error_type
+
+    @property
+    def msg(self):
+        return self.args[0]
+
+    def __str__(self):
+        path = ' @ data[%s]' % ']['.join(map(repr, self.path)) \
+            if self.path else ''
+        output = Exception.__str__(self)
+        if self.error_type:
+            output += ' for ' + self.error_type
+        return output + path
+
+    def prepend(self, path):
+        self.path = path + self.path
+
+
+class MultipleInvalid(Invalid):
+    def __init__(self, errors=None):
+        self.errors = errors[:] if errors else []
+
+    def __repr__(self):
+        return 'MultipleInvalid(%r)' % self.errors
+
+    @property
+    def msg(self):
+        return self.errors[0].msg
+
+    @property
+    def path(self):
+        return self.errors[0].path
+
+    @property
+    def error_message(self):
+        return self.errors[0].error_message
+
+    def add(self, error):
+        self.errors.append(error)
+
+    def __str__(self):
+        return str(self.errors[0])
+
+    def prepend(self, path):
+        for error in self.errors:
+            error.prepend(path)
+
+
+class RequiredFieldInvalid(Invalid):
+    """Required field was missing."""
+
+
+class ObjectInvalid(Invalid):
+    """The value we found was not an object."""
+
+
+class DictInvalid(Invalid):
+    """The value found was not a dict."""
+
+
+class ExclusiveInvalid(Invalid):
+    """More than one value found in exclusion group."""
+
+
+class InclusiveInvalid(Invalid):
+    """Not all values found in inclusion group."""
+
+
+class SequenceTypeInvalid(Invalid):
+    """The type found is not a sequence type."""
+
+
+class TypeInvalid(Invalid):
+    """The value was not of required type."""
+
+
+class ValueInvalid(Invalid):
+    """The value was found invalid by evaluation function."""
+
+
+class ScalarInvalid(Invalid):
+    """Scalars did not match."""
+
+
+class CoerceInvalid(Invalid):
+    """Impossible to coerce value to type."""
+
+
+class AnyInvalid(Invalid):
+    """The value did not pass any validator."""
+
+
+class AllInvalid(Invalid):
+    """The value did not pass all validators."""
+
+
+class MatchInvalid(Invalid):
+    """The value does not match the given regular expression."""
+
+
+class RangeInvalid(Invalid):
+    """The value is not in given range."""
+
+
+class TrueInvalid(Invalid):
+    """The value is not True."""
+
+
+class FalseInvalid(Invalid):
+    """The value is not False."""
+
+
+class BooleanInvalid(Invalid):
+    """The value is not a boolean."""
+
+
+class UrlInvalid(Invalid):
+    """The value is not a url."""
+
+
+class FileInvalid(Invalid):
+    """The value is not a file."""
+
+
+class DirInvalid(Invalid):
+    """The value is not a directory."""
+
+
+class PathInvalid(Invalid):
+    """The value is not a path."""
+
+
+class LiteralInvalid(Invalid):
+    """The literal values do not match."""
+
+
+class VirtualPathComponent(str):
+    def __str__(self):
+        return '<' + self + '>'
+
+    def __repr__(self):
+        return self.__str__()
+
+
+class Schema(object):
+    """A validation schema.
+
+    The schema is a Python tree-like structure where nodes are pattern
+    matched against corresponding trees of values.
+
+    Nodes can be values, in which case a direct comparison is used, types,
+    in which case an isinstance() check is performed, or callables, which will
+    validate and optionally convert the value.
+    """
+
+    _extra_to_name = {
+        REMOVE_EXTRA: 'REMOVE_EXTRA',
+        ALLOW_EXTRA: 'ALLOW_EXTRA',
+        PREVENT_EXTRA: 'PREVENT_EXTRA',
+    }
+
+    def __init__(self, schema, required=False, extra=PREVENT_EXTRA):
+        """Create a new Schema.
+
+        :param schema: Validation schema. See :module:`voluptuous` for details.
+        :param required: Keys defined in the schema must be in the data.
+        :param extra: Specify how extra keys in the data are treated:
+            - :const:`~voluptuous.PREVENT_EXTRA`: to disallow any undefined
+              extra keys (raise ``Invalid``).
+            - :const:`~voluptuous.ALLOW_EXTRA`: to include undefined extra
+              keys in the output.
+            - :const:`~voluptuous.REMOVE_EXTRA`: to exclude undefined extra keys
+              from the output.
+            - Any value other than the above defaults to
+              :const:`~voluptuous.PREVENT_EXTRA`
+        """
+        self.schema = schema
+        self.required = required
+        self.extra = int(extra)  # ensure the value is an integer
+        self._compiled = self._compile(schema)
+
+    def __repr__(self):
+        return "<Schema(%s, extra=%s, required=%s) object at 0x%x>" % (
+            self.schema, self._extra_to_name.get(self.extra, '??'),
+            self.required, id(self))
+
+    def __call__(self, data):
+        """Validate data against this schema."""
+        try:
+            return self._compiled([], data)
+        except MultipleInvalid:
+            raise
+        except Invalid as e:
+            raise MultipleInvalid([e])
+        # return self.validate([], self.schema, data)
+
+    def _compile(self, schema):
+        if schema is Extra:
+            return lambda _, v: v
+        if isinstance(schema, Object):
+            return self._compile_object(schema)
+        if isinstance(schema, collections.Mapping):
+            return self._compile_dict(schema)
+        elif isinstance(schema, list):
+            return self._compile_list(schema)
+        elif isinstance(schema, tuple):
+            return self._compile_tuple(schema)
+        type_ = type(schema)
+        if type_ is type:
+            type_ = schema
+        if type_ in (bool, int, long, str, unicode, float, complex, object,
+                     list, dict, type(None)) or callable(schema):
+            return _compile_scalar(schema)
+        raise SchemaError('unsupported schema data type %r' %
+                          type(schema).__name__)
+
+    def _compile_mapping(self, schema, invalid_msg=None):
+        """Create validator for given mapping."""
+        invalid_msg = invalid_msg or 'mapping value'
+
+        # Keys that may be required
+        all_required_keys = set(key for key in schema
+                                if key is not Extra
+                                and ((self.required and not isinstance(key, (Optional, Remove)))
+                                     or isinstance(key, Required)))
+
+        # Keys that may have defaults
+        all_default_keys = set(key for key in schema
+                               if isinstance(key, Required)
+                               or isinstance(key, Optional))
+
+        _compiled_schema = {}
+        for skey, svalue in iteritems(schema):
+            new_key = self._compile(skey)
+            new_value = self._compile(svalue)
+            _compiled_schema[skey] = (new_key, new_value)
+
+        candidates = list(_iterate_mapping_candidates(_compiled_schema))
+
+        def validate_mapping(path, iterable, out):
+            required_keys = all_required_keys.copy()
+            # keeps track of all default keys that haven't been filled
+            default_keys = all_default_keys.copy()
+            error = None
+            errors = []
+            for key, value in iterable:
+                key_path = path + [key]
+                remove_key = False
+
+                # compare each given key/value against all compiled key/values
+                # schema key, (compiled key, compiled value)
+                for skey, (ckey, cvalue) in candidates:
+                    try:
+                        new_key = ckey(key_path, key)
+                    except Invalid as e:
+                        if len(e.path) > len(key_path):
+                            raise
+                        if not error or len(e.path) > len(error.path):
+                            error = e
+                        continue
+                    # Backtracking is not performed once a key is selected, so if
+                    # the value is invalid we immediately throw an exception.
+                    exception_errors = []
+                    # check if the key is marked for removal
+                    is_remove = new_key is Remove
+                    try:
+                        cval = cvalue(key_path, value)
+                        # include if it's not marked for removal
+                        if not is_remove:
+                            out[new_key] = cval
+                        else:
+                            remove_key = True
+                            continue
+                    except MultipleInvalid as e:
+                        exception_errors.extend(e.errors)
+                    except Invalid as e:
+                        exception_errors.append(e)
+
+                    if exception_errors:
+                        if is_remove or remove_key:
+                            continue
+                        for err in exception_errors:
+                            if len(err.path) <= len(key_path):
+                                err.error_type = invalid_msg
+                            errors.append(err)
+                        # If there is a validation error for a required
+                        # key, this means that the key was provided.
+                        # Discard the required key so it does not
+                        # create an additional, noisy exception.
+                        required_keys.discard(skey)
+                        break
+
+                    # Key and value okay, mark any Required() fields as found.
+                    required_keys.discard(skey)
+
+                    # No need for a default if it was filled
+                    default_keys.discard(skey)
+
+                    break
+                else:
+                    if remove_key:
+                        # remove key
+                        continue
+                    elif self.extra == ALLOW_EXTRA:
+                        out[key] = value
+                    elif self.extra != REMOVE_EXTRA:
+                        errors.append(Invalid('extra keys not allowed', key_path))
+                    # else REMOVE_EXTRA: ignore the key so it's removed from output
+
+            # set defaults for any that can have defaults
+            for key in default_keys:
+                if not isinstance(key.default, Undefined):  # if the user provides a default with the node
+                    out[key.schema] = key.default()
+                    if key in required_keys:
+                        required_keys.discard(key)
+
+            # for any required keys left that weren't found and don't have defaults:
+            for key in required_keys:
+                msg = key.msg if hasattr(key, 'msg') and key.msg else 'required key not provided'
+                errors.append(RequiredFieldInvalid(msg, path + [key]))
+            if errors:
+                raise MultipleInvalid(errors)
+
+            return out
+
+        return validate_mapping
+
+    def _compile_object(self, schema):
+        """Validate an object.
+
+        Has the same behavior as dictionary validator but work with object
+        attributes.
+
+        For example:
+
+            >>> class Structure(object):
+            ...     def __init__(self, one=None, three=None):
+            ...         self.one = one
+            ...         self.three = three
+            ...
+            >>> validate = Schema(Object({'one': 'two', 'three': 'four'}, cls=Structure))
+            >>> with raises(MultipleInvalid, "not a valid value for object value @ data['one']"):
+            ...   validate(Structure(one='three'))
+
+        """
+        base_validate = self._compile_mapping(
+            schema, invalid_msg='object value')
+
+        def validate_object(path, data):
+            if (schema.cls is not UNDEFINED
+                    and not isinstance(data, schema.cls)):
+                raise ObjectInvalid('expected a {0!r}'.format(schema.cls), path)
+            iterable = _iterate_object(data)
+            iterable = ifilter(lambda item: item[1] is not None, iterable)
+            out = base_validate(path, iterable, {})
+            return type(data)(**out)
+
+        return validate_object
+
+    def _compile_dict(self, schema):
+        """Validate a dictionary.
+
+        A dictionary schema can contain a set of values, or at most one
+        validator function/type.
+
+        A dictionary schema will only validate a dictionary:
+
+            >>> validate = Schema({})
+            >>> with raises(MultipleInvalid, 'expected a dictionary'):
+            ...   validate([])
+
+        An invalid dictionary value:
+
+            >>> validate = Schema({'one': 'two', 'three': 'four'})
+            >>> with raises(MultipleInvalid, "not a valid value for dictionary value @ data['one']"):
+            ...   validate({'one': 'three'})
+
+        An invalid key:
+
+            >>> with raises(MultipleInvalid, "extra keys not allowed @ data['two']"):
+            ...   validate({'two': 'three'})
+
+
+        Validation function, in this case the "int" type:
+
+            >>> validate = Schema({'one': 'two', 'three': 'four', int: str})
+
+        Valid integer input:
+
+            >>> validate({10: 'twenty'})
+            {10: 'twenty'}
+
+        By default, a "type" in the schema (in this case "int") will be used
+        purely to validate that the corresponding value is of that type. It
+        will not Coerce the value:
+
+            >>> with raises(MultipleInvalid, "extra keys not allowed @ data['10']"):
+            ...   validate({'10': 'twenty'})
+
+        Wrap them in the Coerce() function to achieve this:
+
+            >>> validate = Schema({'one': 'two', 'three': 'four',
+            ...                    Coerce(int): str})
+            >>> validate({'10': 'twenty'})
+            {10: 'twenty'}
+
+        Custom message for required key
+
+            >>> validate = Schema({Required('one', 'required'): 'two'})
+            >>> with raises(MultipleInvalid, "required @ data['one']"):
+            ...   validate({})
+
+        (This is to avoid unexpected surprises.)
+
+        Multiple errors for nested field in a dict:
+
+        >>> validate = Schema({
+        ...     'adict': {
+        ...         'strfield': str,
+        ...         'intfield': int
+        ...     }
+        ... })
+        >>> try:
+        ...     validate({
+        ...         'adict': {
+        ...             'strfield': 123,
+        ...             'intfield': 'one'
+        ...         }
+        ...     })
+        ... except MultipleInvalid as e:
+        ...     print(sorted(str(i) for i in e.errors)) # doctest: +NORMALIZE_WHITESPACE
+        ["expected int for dictionary value @ data['adict']['intfield']",
+         "expected str for dictionary value @ data['adict']['strfield']"]
+
+        """
+        base_validate = self._compile_mapping(
+            schema, invalid_msg='dictionary value')
+
+        groups_of_exclusion = {}
+        groups_of_inclusion = {}
+        for node in schema:
+            if isinstance(node, Exclusive):
+                g = groups_of_exclusion.setdefault(node.group_of_exclusion, [])
+                g.append(node)
+            elif isinstance(node, Inclusive):
+                g = groups_of_inclusion.setdefault(node.group_of_inclusion, [])
+                g.append(node)
+
+        def validate_dict(path, data):
+            if not isinstance(data, dict):
+                raise DictInvalid('expected a dictionary', path)
+
+            errors = []
+            for label, group in groups_of_exclusion.items():
+                exists = False
+                for exclusive in group:
+                    if exclusive.schema in data:
+                        if exists:
+                            msg = exclusive.msg if hasattr(exclusive, 'msg') and exclusive.msg else \
+                                "two or more values in the same group of exclusion '%s'" % label
+                            next_path = path + [VirtualPathComponent(label)]
+                            errors.append(ExclusiveInvalid(msg, next_path))
+                            break
+                        exists = True
+
+            if errors:
+                raise MultipleInvalid(errors)
+
+            for label, group in groups_of_inclusion.items():
+                included = [node.schema in data for node in group]
+                if any(included) and not all(included):
+                    msg = "some but not all values in the same group of inclusion '%s'" % label
+                    for g in group:
+                        if hasattr(g, 'msg') and g.msg:
+                            msg = g.msg
+                            break
+                    next_path = path + [VirtualPathComponent(label)]
+                    errors.append(InclusiveInvalid(msg, next_path))
+                    break
+
+            if errors:
+                raise MultipleInvalid(errors)
+
+            out = {}
+            return base_validate(path, iteritems(data), out)
+
+        return validate_dict
+
+    def _compile_sequence(self, schema, seq_type):
+        """Validate a sequence type.
+
+        This is a sequence of valid values or validators tried in order.
+
+        >>> validator = Schema(['one', 'two', int])
+        >>> validator(['one'])
+        ['one']
+        >>> with raises(MultipleInvalid, 'expected int @ data[0]'):
+        ...   validator([3.5])
+        >>> validator([1])
+        [1]
+        """
+        _compiled = [self._compile(s) for s in schema]
+        seq_type_name = seq_type.__name__
+
+        def validate_sequence(path, data):
+            if not isinstance(data, seq_type):
+                raise SequenceTypeInvalid('expected a %s' % seq_type_name, path)
+
+            # Empty seq schema, allow any data.
+            if not schema:
+                return data
+
+            out = []
+            invalid = None
+            errors = []
+            index_path = UNDEFINED
+            for i, value in enumerate(data):
+                index_path = path + [i]
+                invalid = None
+                for validate in _compiled:
+                    try:
+                        cval = validate(index_path, value)
+                        if cval is not Remove:  # do not include Remove values
+                            out.append(cval)
+                        break
+                    except Invalid as e:
+                        if len(e.path) > len(index_path):
+                            raise
+                        invalid = e
+                else:
+                    errors.append(invalid)
+            if errors:
+                raise MultipleInvalid(errors)
+            return type(data)(out)
+        return validate_sequence
+
+    def _compile_tuple(self, schema):
+        """Validate a tuple.
+
+        A tuple is a sequence of valid values or validators tried in order.
+
+        >>> validator = Schema(('one', 'two', int))
+        >>> validator(('one',))
+        ('one',)
+        >>> with raises(MultipleInvalid, 'expected int @ data[0]'):
+        ...   validator((3.5,))
+        >>> validator((1,))
+        (1,)
+        """
+        return self._compile_sequence(schema, tuple)
+
+    def _compile_list(self, schema):
+        """Validate a list.
+
+        A list is a sequence of valid values or validators tried in order.
+
+        >>> validator = Schema(['one', 'two', int])
+        >>> validator(['one'])
+        ['one']
+        >>> with raises(MultipleInvalid, 'expected int @ data[0]'):
+        ...   validator([3.5])
+        >>> validator([1])
+        [1]
+        """
+        return self._compile_sequence(schema, list)
+
+    def extend(self, schema, required=None, extra=None):
+        """Create a new `Schema` by merging this and the provided `schema`.
+
+        Neither this `Schema` nor the provided `schema` are modified. The
+        resulting `Schema` inherits the `required` and `extra` parameters of
+        this, unless overridden.
+
+        Both schemas must be dictionary-based.
+
+        :param schema: dictionary to extend this `Schema` with
+        :param required: if set, overrides `required` of this `Schema`
+        :param extra: if set, overrides `extra` of this `Schema`
+        """
+
+        assert type(self.schema) == dict and type(schema) == dict, 'Both schemas must be dictionary-based'
+
+        result = self.schema.copy()
+        result.update(schema)
+
+        result_required = (required if required is not None else self.required)
+        result_extra = (extra if extra is not None else self.extra)
+        return Schema(result, required=result_required, extra=result_extra)
+
+
+def _compile_scalar(schema):
+    """A scalar value.
+
+    The schema can either be a value or a type.
+
+    >>> _compile_scalar(int)([], 1)
+    1
+    >>> with raises(Invalid, 'expected float'):
+    ...   _compile_scalar(float)([], '1')
+
+    Callables have
+    >>> _compile_scalar(lambda v: float(v))([], '1')
+    1.0
+
+    As a convenience, ValueError's are trapped:
+
+    >>> with raises(Invalid, 'not a valid value'):
+    ...   _compile_scalar(lambda v: float(v))([], 'a')
+    """
+    if isinstance(schema, type):
+        def validate_instance(path, data):
+            if isinstance(data, schema):
+                return data
+            else:
+                msg = 'expected %s' % schema.__name__
+                raise TypeInvalid(msg, path)
+        return validate_instance
+
+    if callable(schema):
+        def validate_callable(path, data):
+            try:
+                return schema(data)
+            except ValueError as e:
+                raise ValueInvalid('not a valid value', path)
+            except Invalid as e:
+                e.prepend(path)
+                raise
+        return validate_callable
+
+    def validate_value(path, data):
+        if data != schema:
+            raise ScalarInvalid('not a valid value', path)
+        return data
+
+    return validate_value
+
+
+def _compile_itemsort():
+    '''return sort function of mappings'''
+    def is_extra(key_):
+        return key_ is Extra
+
+    def is_remove(key_):
+        return isinstance(key_, Remove)
+
+    def is_marker(key_):
+        return isinstance(key_, Marker)
+
+    def is_type(key_):
+        return inspect.isclass(key_)
+
+    def is_callable(key_):
+        return callable(key_)
+
+    # priority list for map sorting (in order of checking)
+    # We want Extra to match last, because it's a catch-all. On the other hand,
+    # Remove markers should match first (since invalid values will not
+    # raise an Error, instead the validator will check if other schemas match
+    # the same value).
+    priority = [(1, is_remove),    # Remove highest priority after values
+                (2, is_marker),    # then other Markers
+                (4, is_type),      # types/classes lowest before Extra
+                (3, is_callable),  # callables after markers
+                (5, is_extra)]     # Extra lowest priority
+
+    def item_priority(item_):
+        key_ = item_[0]
+        for i, check_ in priority:
+            if check_(key_):
+                return i
+        # values have hightest priorities
+        return 0
+
+    return item_priority
+
+_sort_item = _compile_itemsort()
+
+
+def _iterate_mapping_candidates(schema):
+    """Iterate over schema in a meaningful order."""
+    # Without this, Extra might appear first in the iterator, and fail to
+    # validate a key even though it's a Required that has its own validation,
+    # generating a false positive.
+    return sorted(iteritems(schema), key=_sort_item)
+
+
+def _iterate_object(obj):
+    """Return iterator over object attributes. Respect objects with
+    defined __slots__.
+
+    """
+    d = {}
+    try:
+        d = vars(obj)
+    except TypeError:
+        # maybe we have named tuple here?
+        if hasattr(obj, '_asdict'):
+            d = obj._asdict()
+    for item in iteritems(d):
+        yield item
+    try:
+        slots = obj.__slots__
+    except AttributeError:
+        pass
+    else:
+        for key in slots:
+            if key != '__dict__':
+                yield (key, getattr(obj, key))
+    raise StopIteration()
+
+
+class Object(dict):
+    """Indicate that we should work with attributes, not keys."""
+
+    def __init__(self, schema, cls=UNDEFINED):
+        self.cls = cls
+        super(Object, self).__init__(schema)
+
+
+class Marker(object):
+    """Mark nodes for special treatment."""
+
+    def __init__(self, schema, msg=None):
+        self.schema = schema
+        self._schema = Schema(schema)
+        self.msg = msg
+
+    def __call__(self, v):
+        try:
+            return self._schema(v)
+        except Invalid as e:
+            if not self.msg or len(e.path) > 1:
+                raise
+            raise Invalid(self.msg)
+
+    def __str__(self):
+        return str(self.schema)
+
+    def __repr__(self):
+        return repr(self.schema)
+
+    def __lt__(self, other):
+        return self.schema < other.schema
+
+
+class Optional(Marker):
+    """Mark a node in the schema as optional, and optionally provide a default
+
+    >>> schema = Schema({Optional('key'): str})
+    >>> schema({})
+    {}
+    >>> schema = Schema({Optional('key', default='value'): str})
+    >>> schema({})
+    {'key': 'value'}
+    >>> schema = Schema({Optional('key', default=list): list})
+    >>> schema({})
+    {'key': []}
+
+    If 'required' flag is set for an entire schema, optional keys aren't required
+
+    >>> schema = Schema({
+    ...    Optional('key'): str,
+    ...    'key2': str
+    ... }, required=True)
+    >>> schema({'key2':'value'})
+    {'key2': 'value'}
+    """
+    def __init__(self, schema, msg=None, default=UNDEFINED):
+        super(Optional, self).__init__(schema, msg=msg)
+        self.default = default_factory(default)
+
+
+class Exclusive(Optional):
+    """Mark a node in the schema as exclusive.
+
+    Exclusive keys inherited from Optional:
+
+    >>> schema = Schema({Exclusive('alpha', 'angles'): int, Exclusive('beta', 'angles'): int})
+    >>> schema({'alpha': 30})
+    {'alpha': 30}
+
+    Keys inside a same group of exclusion cannot be together, it only makes sense for dictionaries:
+
+    >>> with raises(MultipleInvalid, "two or more values in the same group of exclusion 'angles' @ data[<angles>]"):
+    ...   schema({'alpha': 30, 'beta': 45})
+
+    For example, API can provides multiple types of authentication, but only one works in the same time:
+
+    >>> msg = 'Please, use only one type of authentication at the same time.'
+    >>> schema = Schema({
+    ... Exclusive('classic', 'auth', msg=msg):{
+    ...     Required('email'): basestring,
+    ...     Required('password'): basestring
+    ...     },
+    ... Exclusive('internal', 'auth', msg=msg):{
+    ...     Required('secret_key'): basestring
+    ...     },
+    ... Exclusive('social', 'auth', msg=msg):{
+    ...     Required('social_network'): basestring,
+    ...     Required('token'): basestring
+    ...     }
+    ... })
+
+    >>> with raises(MultipleInvalid, "Please, use only one type of authentication at the same time. @ data[<auth>]"):
+    ...     schema({'classic': {'email': 'foo@example.com', 'password': 'bar'},
+    ...             'social': {'social_network': 'barfoo', 'token': 'tEMp'}})
+    """
+    def __init__(self, schema, group_of_exclusion, msg=None):
+        super(Exclusive, self).__init__(schema, msg=msg)
+        self.group_of_exclusion = group_of_exclusion
+
+
+class Inclusive(Optional):
+    """ Mark a node in the schema as inclusive.
+
+    Exclusive keys inherited from Optional:
+
+    >>> schema = Schema({
+    ...     Inclusive('filename', 'file'): str,
+    ...     Inclusive('mimetype', 'file'): str
+    ... })
+    >>> data = {'filename': 'dog.jpg', 'mimetype': 'image/jpeg'}
+    >>> data == schema(data)
+    True
+
+    Keys inside a same group of inclusive must exist together, it only makes sense for dictionaries:
+
+    >>> with raises(MultipleInvalid, "some but not all values in the same group of inclusion 'file' @ data[<file>]"):
+    ...     schema({'filename': 'dog.jpg'})
+
+    If none of the keys in the group are present, it is accepted:
+
+    >>> schema({})
+    {}
+
+    For example, API can return 'height' and 'width' together, but not separately.
+
+    >>> msg = "Height and width must exist together"
+    >>> schema = Schema({
+    ...     Inclusive('height', 'size', msg=msg): int,
+    ...     Inclusive('width', 'size', msg=msg): int
+    ... })
+
+    >>> with raises(MultipleInvalid, msg + " @ data[<size>]"):
+    ...     schema({'height': 100})
+
+    >>> with raises(MultipleInvalid, msg + " @ data[<size>]"):
+    ...     schema({'width': 100})
+
+    >>> data = {'height': 100, 'width': 100}
+    >>> data == schema(data)
+    True
+    """
+
+    def __init__(self, schema, group_of_inclusion, msg=None):
+        super(Inclusive, self).__init__(schema, msg=msg)
+        self.group_of_inclusion = group_of_inclusion
+
+
+class Required(Marker):
+    """Mark a node in the schema as being required, and optionally provide a default value.
+
+    >>> schema = Schema({Required('key'): str})
+    >>> with raises(MultipleInvalid, "required key not provided @ data['key']"):
+    ...   schema({})
+
+    >>> schema = Schema({Required('key', default='value'): str})
+    >>> schema({})
+    {'key': 'value'}
+    >>> schema = Schema({Required('key', default=list): list})
+    >>> schema({})
+    {'key': []}
+    """
+    def __init__(self, schema, msg=None, default=UNDEFINED):
+        super(Required, self).__init__(schema, msg=msg)
+        self.default = default_factory(default)
+
+
+class Remove(Marker):
+    """Mark a node in the schema to be removed and excluded from the validated
+    output. Keys that fail validation will not raise ``Invalid``. Instead, these
+    keys will be treated as extras.
+
+    >>> schema = Schema({str: int, Remove(int): str})
+    >>> with raises(MultipleInvalid, "extra keys not allowed @ data[1]"):
+    ...    schema({'keep': 1, 1: 1.0})
+    >>> schema({1: 'red', 'red': 1, 2: 'green'})
+    {'red': 1}
+    >>> schema = Schema([int, Remove(float), Extra])
+    >>> schema([1, 2, 3, 4.0, 5, 6.0, '7'])
+    [1, 2, 3, 5, '7']
+    """
+    def __call__(self, v):
+        super(Remove, self).__call__(v)
+        return self.__class__
+
+    def __repr__(self):
+        return "Remove(%r)" % (self.schema,)
+
+
+def Extra(_):
+    """Allow keys in the data that are not present in the schema."""
+    raise SchemaError('"Extra" should never be called')
+
+
+# As extra() is never called there's no way to catch references to the
+# deprecated object, so we just leave an alias here instead.
+extra = Extra
+
+class Msg(object):
+    """Report a user-friendly message if a schema fails to validate.
+
+    >>> validate = Schema(
+    ...   Msg(['one', 'two', int],
+    ...       'should be one of "one", "two" or an integer'))
+    >>> with raises(MultipleInvalid, 'should be one of "one", "two" or an integer'):
+    ...   validate(['three'])
+
+    Messages are only applied to invalid direct descendants of the schema:
+
+    >>> validate = Schema(Msg([['one', 'two', int]], 'not okay!'))
+    >>> with raises(MultipleInvalid, 'expected int @ data[0][0]'):
+    ...   validate([['three']])
+
+    The type which is thrown can be overridden but needs to be a subclass of Invalid
+
+    >>> with raises(SchemaError, 'Msg can only use subclases of Invalid as custom class'):
+    ...   validate = Schema(Msg([int], 'should be int', cls=KeyError))
+
+    If you do use a subclass of Invalid, that error will be thrown (wrapped in a MultipleInvalid)
+
+    >>> validate = Schema(Msg([['one', 'two', int]], 'not okay!', cls=RangeInvalid))
+    >>> try:
+    ...  validate(['three'])
+    ... except MultipleInvalid as e:
+    ...   assert isinstance(e.errors[0], RangeInvalid)
+    """
+
+    def __init__(self, schema, msg, cls=None):
+        if cls and not issubclass(cls, Invalid):
+            raise SchemaError("Msg can only use subclases of"
+                              " Invalid as custom class")
+        self._schema = schema
+        self.schema = Schema(schema)
+        self.msg = msg
+        self.cls = cls
+
+    def __call__(self, v):
+        try:
+            return self.schema(v)
+        except Invalid as e:
+            if len(e.path) > 1:
+                raise e
+            else:
+                raise (self.cls or Invalid)(self.msg)
+
+    def __repr__(self):
+        return 'Msg(%s, %s, cls=%s)' % (self._schema, self.msg, self.cls)
+
+
+def message(default=None, cls=None):
+    """Convenience decorator to allow functions to provide a message.
+
+    Set a default message:
+
+        >>> @message('not an integer')
+        ... def isint(v):
+        ...   return int(v)
+
+        >>> validate = Schema(isint())
+        >>> with raises(MultipleInvalid, 'not an integer'):
+        ...   validate('a')
+
+    The message can be overridden on a per validator basis:
+
+        >>> validate = Schema(isint('bad'))
+        >>> with raises(MultipleInvalid, 'bad'):
+        ...   validate('a')
+
+    The class thrown too:
+
+        >>> class IntegerInvalid(Invalid): pass
+        >>> validate = Schema(isint('bad', clsoverride=IntegerInvalid))
+        >>> try:
+        ...  validate('a')
+        ... except MultipleInvalid as e:
+        ...   assert isinstance(e.errors[0], IntegerInvalid)
+    """
+    if cls and not issubclass(cls, Invalid):
+        raise SchemaError("message can only use subclases of Invalid as custom class")
+
+    def decorator(f):
+        @wraps(f)
+        def check(msg=None, clsoverride=None):
+            @wraps(f)
+            def wrapper(*args, **kwargs):
+                try:
+                    return f(*args, **kwargs)
+                except ValueError:
+                    raise (clsoverride or cls or ValueInvalid)(msg or default or 'invalid value')
+            return wrapper
+        return check
+    return decorator
+
+
+def truth(f):
+    """Convenience decorator to convert truth functions into validators.
+
+        >>> @truth
+        ... def isdir(v):
+        ...   return os.path.isdir(v)
+        >>> validate = Schema(isdir)
+        >>> validate('/')
+        '/'
+        >>> with raises(MultipleInvalid, 'not a valid value'):
+        ...   validate('/notavaliddir')
+    """
+    @wraps(f)
+    def check(v):
+        t = f(v)
+        if not t:
+            raise ValueError
+        return v
+    return check
+
+
+class Coerce(object):
+    """Coerce a value to a type.
+
+    If the type constructor throws a ValueError or TypeError, the value
+    will be marked as Invalid.
+
+    Default behavior:
+
+        >>> validate = Schema(Coerce(int))
+        >>> with raises(MultipleInvalid, 'expected int'):
+        ...   validate(None)
+        >>> with raises(MultipleInvalid, 'expected int'):
+        ...   validate('foo')
+
+    With custom message:
+
+        >>> validate = Schema(Coerce(int, "moo"))
+        >>> with raises(MultipleInvalid, 'moo'):
+        ...   validate('foo')
+    """
+
+    def __init__(self, type, msg=None):
+        self.type = type
+        self.msg = msg
+        self.type_name = type.__name__
+
+    def __call__(self, v):
+        try:
+            return self.type(v)
+        except (ValueError, TypeError):
+            msg = self.msg or ('expected %s' % self.type_name)
+            raise CoerceInvalid(msg)
+
+    def __repr__(self):
+        return 'Coerce(%s, msg=%r)' % (self.type_name, self.msg)
+
+
+@message('value was not true', cls=TrueInvalid)
+@truth
+def IsTrue(v):
+    """Assert that a value is true, in the Python sense.
+
+    >>> validate = Schema(IsTrue())
+
+    "In the Python sense" means that implicitly false values, such as empty
+    lists, dictionaries, etc. are treated as "false":
+
+    >>> with raises(MultipleInvalid, "value was not true"):
+    ...   validate([])
+    >>> validate([1])
+    [1]
+    >>> with raises(MultipleInvalid, "value was not true"):
+    ...   validate(False)
+
+    ...and so on.
+
+    >>> try:
+    ...  validate([])
+    ... except MultipleInvalid as e:
+    ...   assert isinstance(e.errors[0], TrueInvalid)
+    """
+    return v
+
+
+@message('value was not false', cls=FalseInvalid)
+def IsFalse(v):
+    """Assert that a value is false, in the Python sense.
+
+    (see :func:`IsTrue` for more detail)
+
+    >>> validate = Schema(IsFalse())
+    >>> validate([])
+    []
+    >>> with raises(MultipleInvalid, "value was not false"):
+    ...   validate(True)
+
+    >>> try:
+    ...  validate(True)
+    ... except MultipleInvalid as e:
+    ...   assert isinstance(e.errors[0], FalseInvalid)
+    """
+    if v:
+        raise ValueError
+    return v
+
+
+@message('expected boolean', cls=BooleanInvalid)
+def Boolean(v):
+    """Convert human-readable boolean values to a bool.
+
+    Accepted values are 1, true, yes, on, enable, and their negatives.
+    Non-string values are cast to bool.
+
+    >>> validate = Schema(Boolean())
+    >>> validate(True)
+    True
+    >>> validate("1")
+    True
+    >>> validate("0")
+    False
+    >>> with raises(MultipleInvalid, "expected boolean"):
+    ...   validate('moo')
+    >>> try:
+    ...  validate('moo')
+    ... except MultipleInvalid as e:
+    ...   assert isinstance(e.errors[0], BooleanInvalid)
+    """
+    if isinstance(v, basestring):
+        v = v.lower()
+        if v in ('1', 'true', 'yes', 'on', 'enable'):
+            return True
+        if v in ('0', 'false', 'no', 'off', 'disable'):
+            return False
+        raise ValueError
+    return bool(v)
+
+
+class Any(object):
+    """Use the first validated value.
+
+    :param msg: Message to deliver to user if validation fails.
+    :param kwargs: All other keyword arguments are passed to the sub-Schema constructors.
+    :returns: Return value of the first validator that passes.
+
+    >>> validate = Schema(Any('true', 'false',
+    ...                       All(Any(int, bool), Coerce(bool))))
+    >>> validate('true')
+    'true'
+    >>> validate(1)
+    True
+    >>> with raises(MultipleInvalid, "not a valid value"):
+    ...   validate('moo')
+
+    msg argument is used
+
+    >>> validate = Schema(Any(1, 2, 3, msg="Expected 1 2 or 3"))
+    >>> validate(1)
+    1
+    >>> with raises(MultipleInvalid, "Expected 1 2 or 3"):
+    ...   validate(4)
+    """
+
+    def __init__(self, *validators, **kwargs):
+        self.validators = validators
+        self.msg = kwargs.pop('msg', None)
+        self._schemas = [Schema(val, **kwargs) for val in validators]
+
+    def __call__(self, v):
+        error = None
+        for schema in self._schemas:
+            try:
+                return schema(v)
+            except Invalid as e:
+                if error is None or len(e.path) > len(error.path):
+                    error = e
+        else:
+            if error:
+                raise error if self.msg is None else AnyInvalid(self.msg)
+            raise AnyInvalid(self.msg or 'no valid value found')
+
+    def __repr__(self):
+        return 'Any([%s])' % (", ".join(repr(v) for v in self.validators))
+
+
+# Convenience alias
+Or = Any
+
+
+class All(object):
+    """Value must pass all validators.
+
+    The output of each validator is passed as input to the next.
+
+    :param msg: Message to deliver to user if validation fails.
+    :param kwargs: All other keyword arguments are passed to the sub-Schema constructors.
+
+    >>> validate = Schema(All('10', Coerce(int)))
+    >>> validate('10')
+    10
+    """
+
+    def __init__(self, *validators, **kwargs):
+        self.validators = validators
+        self.msg = kwargs.pop('msg', None)
+        self._schemas = [Schema(val, **kwargs) for val in validators]
+
+    def __call__(self, v):
+        try:
+            for schema in self._schemas:
+                v = schema(v)
+        except Invalid as e:
+            raise e if self.msg is None else AllInvalid(self.msg)
+        return v
+
+    def __repr__(self):
+        return 'All(%s, msg=%r)' % (
+            ", ".join(repr(v) for v in self.validators),
+            self.msg
+        )
+
+
+# Convenience alias
+And = All
+
+
+class Match(object):
+    """Value must be a string that matches the regular expression.
+
+    >>> validate = Schema(Match(r'^0x[A-F0-9]+$'))
+    >>> validate('0x123EF4')
+    '0x123EF4'
+    >>> with raises(MultipleInvalid, "does not match regular expression"):
+    ...   validate('123EF4')
+
+    >>> with raises(MultipleInvalid, 'expected string or buffer'):
+    ...   validate(123)
+
+    Pattern may also be a _compiled regular expression:
+
+    >>> validate = Schema(Match(re.compile(r'0x[A-F0-9]+', re.I)))
+    >>> validate('0x123ef4')
+    '0x123ef4'
+    """
+
+    def __init__(self, pattern, msg=None):
+        if isinstance(pattern, basestring):
+            pattern = re.compile(pattern)
+        self.pattern = pattern
+        self.msg = msg
+
+    def __call__(self, v):
+        try:
+            match = self.pattern.match(v)
+        except TypeError:
+            raise MatchInvalid("expected string or buffer")
+        if not match:
+            raise MatchInvalid(self.msg or 'does not match regular expression')
+        return v
+
+    def __repr__(self):
+        return 'Match(%r, msg=%r)' % (self.pattern.pattern, self.msg)
+
+
+class Replace(object):
+    """Regex substitution.
+
+    >>> validate = Schema(All(Replace('you', 'I'),
+    ...                       Replace('hello', 'goodbye')))
+    >>> validate('you say hello')
+    'I say goodbye'
+    """
+
+    def __init__(self, pattern, substitution, msg=None):
+        if isinstance(pattern, basestring):
+            pattern = re.compile(pattern)
+        self.pattern = pattern
+        self.substitution = substitution
+        self.msg = msg
+
+    def __call__(self, v):
+        return self.pattern.sub(self.substitution, v)
+
+    def __repr__(self):
+        return 'Replace(%r, %r, msg=%r)' % (self.pattern.pattern,
+                                            self.substitution,
+                                            self.msg)
+
+
+def _url_validation(v):
+    parsed = urlparse.urlparse(v)
+    if not parsed.scheme or not parsed.netloc:
+        raise UrlInvalid("must have a URL scheme and host")
+    return parsed
+
+
+@message('expected a Fully qualified domain name URL', cls=UrlInvalid)
+def FqdnUrl(v):
+    """Verify that the value is a Fully qualified domain name URL.
+
+    >>> s = Schema(FqdnUrl())
+    >>> with raises(MultipleInvalid, 'expected a Fully qualified domain name URL'):
+    ...   s("http://localhost/")
+    >>> s('http://w3.org')
+    'http://w3.org'
+    """
+    try:
+        parsed_url = _url_validation(v)
+        if "." not in parsed_url.netloc:
+            raise UrlInvalid("must have a domain name in URL")
+        return v
+    except:
+        raise ValueError
+
+
+@message('expected a URL', cls=UrlInvalid)
+def Url(v):
+    """Verify that the value is a URL.
+
+    >>> s = Schema(Url())
+    >>> with raises(MultipleInvalid, 'expected a URL'):
+    ...   s(1)
+    >>> s('http://w3.org')
+    'http://w3.org'
+    """
+    try:
+        _url_validation(v)
+        return v
+    except:
+        raise ValueError
+
+
+@message('not a file', cls=FileInvalid)
+@truth
+def IsFile(v):
+    """Verify the file exists.
+
+    >>> os.path.basename(IsFile()(__file__)).startswith('voluptuous.py')
+    True
+    >>> with raises(FileInvalid, 'not a file'):
+    ...   IsFile()("random_filename_goes_here.py")
+    """
+    return os.path.isfile(v)
+
+
+@message('not a directory', cls=DirInvalid)
+@truth
+def IsDir(v):
+    """Verify the directory exists.
+
+    >>> IsDir()('/')
+    '/'
+    """
+    return os.path.isdir(v)
+
+
+@message('path does not exist', cls=PathInvalid)
+@truth
+def PathExists(v):
+    """Verify the path exists, regardless of its type.
+
+    >>> os.path.basename(PathExists()(__file__)).startswith('voluptuous.py')
+    True
+    >>> with raises(Invalid, 'path does not exist'):
+    ...   PathExists()("random_filename_goes_here.py")
+    """
+    return os.path.exists(v)
+
+
+class Range(object):
+    """Limit a value to a range.
+
+    Either min or max may be omitted.
+    Either min or max can be excluded from the range of accepted values.
+
+    :raises Invalid: If the value is outside the range.
+
+    >>> s = Schema(Range(min=1, max=10, min_included=False))
+    >>> s(5)
+    5
+    >>> s(10)
+    10
+    >>> with raises(MultipleInvalid, 'value must be at most 10'):
+    ...   s(20)
+    >>> with raises(MultipleInvalid, 'value must be higher than 1'):
+    ...   s(1)
+    >>> with raises(MultipleInvalid, 'value must be lower than 10'):
+    ...   Schema(Range(max=10, max_included=False))(20)
+    """
+
+    def __init__(self, min=None, max=None, min_included=True,
+                 max_included=True, msg=None):
+        self.min = min
+        self.max = max
+        self.min_included = min_included
+        self.max_included = max_included
+        self.msg = msg
+
+    def __call__(self, v):
+        if self.min_included:
+            if self.min is not None and v < self.min:
+                raise RangeInvalid(
+                    self.msg or 'value must be at least %s' % self.min)
+        else:
+            if self.min is not None and v <= self.min:
+                raise RangeInvalid(
+                    self.msg or 'value must be higher than %s' % self.min)
+        if self.max_included:
+            if self.max is not None and v > self.max:
+                raise RangeInvalid(
+                    self.msg or 'value must be at most %s' % self.max)
+        else:
+            if self.max is not None and v >= self.max:
+                raise RangeInvalid(
+                    self.msg or 'value must be lower than %s' % self.max)
+        return v
+
+    def __repr__(self):
+        return ('Range(min=%r, max=%r, min_included=%r,'
+                ' max_included=%r, msg=%r)' % (self.min, self.max,
+                                               self.min_included,
+                                               self.max_included,
+                                               self.msg))
+
+
+class Clamp(object):
+    """Clamp a value to a range.
+
+    Either min or max may be omitted.
+    >>> s = Schema(Clamp(min=0, max=1))
+    >>> s(0.5)
+    0.5
+    >>> s(5)
+    1
+    >>> s(-1)
+    0
+    """
+
+    def __init__(self, min=None, max=None, msg=None):
+        self.min = min
+        self.max = max
+        self.msg = msg
+
+    def __call__(self, v):
+        if self.min is not None and v < self.min:
+            v = self.min
+        if self.max is not None and v > self.max:
+            v = self.max
+        return v
+
+    def __repr__(self):
+        return 'Clamp(min=%s, max=%s)' % (self.min, self.max)
+
+
+class LengthInvalid(Invalid):
+    pass
+
+
+class Length(object):
+    """The length of a value must be in a certain range."""
+
+    def __init__(self, min=None, max=None, msg=None):
+        self.min = min
+        self.max = max
+        self.msg = msg
+
+    def __call__(self, v):
+        if self.min is not None and len(v) < self.min:
+            raise LengthInvalid(
+                self.msg or 'length of value must be at least %s' % self.min)
+        if self.max is not None and len(v) > self.max:
+            raise LengthInvalid(
+                self.msg or 'length of value must be at most %s' % self.max)
+        return v
+
+    def __repr__(self):
+        return 'Length(min=%s, max=%s)' % (self.min, self.max)
+
+
+class DatetimeInvalid(Invalid):
+    """The value is not a formatted datetime string."""
+
+
+class Datetime(object):
+    """Validate that the value matches the datetime format."""
+
+    DEFAULT_FORMAT = '%Y-%m-%dT%H:%M:%S.%fZ'
+
+    def __init__(self, format=None, msg=None):
+        self.format = format or self.DEFAULT_FORMAT
+        self.msg = msg
+
+    def __call__(self, v):
+        try:
+            datetime.datetime.strptime(v, self.format)
+        except (TypeError, ValueError):
+            raise DatetimeInvalid(
+                self.msg or 'value does not match'
+                            ' expected format %s' % self.format)
+        return v
+
+    def __repr__(self):
+        return 'Datetime(format=%s)' % self.format
+
+
+class InInvalid(Invalid):
+    pass
+
+
+class In(object):
+    """Validate that a value is in a collection."""
+
+    def __init__(self, container, msg=None):
+        self.container = container
+        self.msg = msg
+
+    def __call__(self, v):
+        try:
+            check = v not in self.container
+        except TypeError:
+            check = True
+        if check:
+            raise InInvalid(self.msg or 'value is not allowed')
+        return v
+
+    def __repr__(self):
+        return 'In(%s)' % (self.container,)
+
+
+class NotInInvalid(Invalid):
+    pass
+
+
+class NotIn(object):
+    """Validate that a value is not in a collection."""
+
+    def __init__(self, container, msg=None):
+        self.container = container
+        self.msg = msg
+
+    def __call__(self, v):
+        try:
+            check = v in self.container
+        except TypeError:
+            check = True
+        if check:
+            raise NotInInvalid(self.msg or 'value is not allowed')
+        return v
+
+    def __repr__(self):
+        return 'NotIn(%s)' % (self.container,)
+
+
+def Lower(v):
+    """Transform a string to lower case.
+
+    >>> s = Schema(Lower)
+    >>> s('HI')
+    'hi'
+    """
+    return str(v).lower()
+
+
+def Upper(v):
+    """Transform a string to upper case.
+
+    >>> s = Schema(Upper)
+    >>> s('hi')
+    'HI'
+    """
+    return str(v).upper()
+
+
+def Capitalize(v):
+    """Capitalise a string.
+
+    >>> s = Schema(Capitalize)
+    >>> s('hello world')
+    'Hello world'
+    """
+    return str(v).capitalize()
+
+
+def Title(v):
+    """Title case a string.
+
+    >>> s = Schema(Title)
+    >>> s('hello world')
+    'Hello World'
+    """
+    return str(v).title()
+
+
+def Strip(v):
+    """Strip whitespace from a string.
+
+    >>> s = Schema(Strip)
+    >>> s('  hello world  ')
+    'hello world'
+    """
+    return str(v).strip()
+
+
+class DefaultTo(object):
+    """Sets a value to default_value if none provided.
+
+    >>> s = Schema(DefaultTo(42))
+    >>> s(None)
+    42
+    >>> s = Schema(DefaultTo(list))
+    >>> s(None)
+    []
+    """
+
+    def __init__(self, default_value, msg=None):
+        self.default_value = default_factory(default_value)
+        self.msg = msg
+
+    def __call__(self, v):
+        if v is None:
+            v = self.default_value()
+        return v
+
+    def __repr__(self):
+        return 'DefaultTo(%s)' % (self.default_value(),)
+
+
+class SetTo(object):
+    """Set a value, ignoring any previous value.
+
+    >>> s = Schema(Any(int, SetTo(42)))
+    >>> s(2)
+    2
+    >>> s("foo")
+    42
+    """
+
+    def __init__(self, value):
+        self.value = default_factory(value)
+
+    def __call__(self, v):
+        return self.value()
+
+    def __repr__(self):
+        return 'SetTo(%s)' % (self.value(),)
+
+
+class ExactSequenceInvalid(Invalid):
+    pass
+
+
+class ExactSequence(object):
+    """Matches each element in a sequence against the corresponding element in
+    the validators.
+
+    :param msg: Message to deliver to user if validation fails.
+    :param kwargs: All other keyword arguments are passed to the sub-Schema
+        constructors.
+
+    >>> from voluptuous import *
+    >>> validate = Schema(ExactSequence([str, int, list, list]))
+    >>> validate(['hourly_report', 10, [], []])
+    ['hourly_report', 10, [], []]
+    >>> validate(('hourly_report', 10, [], []))
+    ('hourly_report', 10, [], [])
+    """
+
+    def __init__(self, validators, **kwargs):
+        self.validators = validators
+        self.msg = kwargs.pop('msg', None)
+        self._schemas = [Schema(val, **kwargs) for val in validators]
+
+    def __call__(self, v):
+        if not isinstance(v, (list, tuple)):
+            raise ExactSequenceInvalid(self.msg)
+        try:
+            v = type(v)(schema(x) for x, schema in zip(v, self._schemas))
+        except Invalid as e:
+            raise e if self.msg is None else ExactSequenceInvalid(self.msg)
+        return v
+
+    def __repr__(self):
+        return 'ExactSequence([%s])' % (", ".join(repr(v)
+                                                  for v in self.validators))
+
+
+class Literal(object):
+    def __init__(self, lit):
+        self.lit = lit
+
+    def __call__(self, value, msg=None):
+        if self.lit != value:
+            raise LiteralInvalid(
+                msg or '%s not match for %s' % (value, self.lit)
+            )
+        else:
+            return self.lit
+
+    def __str__(self):
+        return str(self.lit)
+
+    def __repr__(self):
+        return repr(self.lit)
+
+
+class Unique(object):
+    """Ensure an iterable does not contain duplicate items.
+
+    Only iterables convertable to a set are supported (native types and
+    objects with correct __eq__).
+
+    JSON does not support set, so they need to be presented as arrays.
+    Unique allows ensuring that such array does not contain dupes.
+
+    >>> s = Schema(Unique())
+    >>> s([])
+    []
+    >>> s([1, 2])
+    [1, 2]
+    >>> with raises(Invalid, 'contains duplicate items: [1]'):
+    ...   s([1, 1, 2])
+    >>> with raises(Invalid, "contains duplicate items: ['one']"):
+    ...   s(['one', 'two', 'one'])
+    >>> with raises(Invalid, regex="^contains unhashable elements: "):
+    ...   s([set([1, 2]), set([3, 4])])
+    >>> s('abc')
+    'abc'
+    >>> with raises(Invalid, regex="^contains duplicate items: "):
+    ...   s('aabbc')
+    """
+
+    def __init__(self, msg=None):
+        self.msg = msg
+
+    def __call__(self, v):
+        try:
+            set_v = set(v)
+        except TypeError as e:
+            raise TypeInvalid(
+                self.msg or 'contains unhashable elements: {0}'.format(e))
+        if len(set_v) != len(v):
+            seen = set()
+            dupes = list(set(x for x in v if x in seen or seen.add(x)))
+            raise Invalid(
+                self.msg or 'contains duplicate items: {0}'.format(dupes))
+        return v
+
+    def __repr__(self):
+        return 'Unique()'
+
+
+class Set(object):
+    """Convert a list into a set.
+
+    >>> s = Schema(Set())
+    >>> s([]) == set([])
+    True
+    >>> s([1, 2]) == set([1, 2])
+    True
+    >>> with raises(Invalid, regex="^cannot be presented as set: "):
+    ...   s([set([1, 2]), set([3, 4])])
+    """
+
+    def __init__(self, msg=None):
+        self.msg = msg
+
+    def __call__(self, v):
+        try:
+            set_v = set(v)
+        except Exception as e:
+            raise TypeInvalid(
+                self.msg or 'cannot be presented as set: {0}'.format(e))
+        return set_v
+
+    def __repr__(self):
+        return 'Set()'
+
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()