path: root/contrib/python/PyYAML/py2/yaml/constructor.py

__all__ = [ 
    'BaseConstructor', 
    'SafeConstructor', 
    'FullConstructor', 
    'UnsafeConstructor', 
    'Constructor', 
    'ConstructorError' 
] 

from error import *
from nodes import *

import datetime

import binascii, re, sys, types

class ConstructorError(MarkedYAMLError):
    pass

 
class timezone(datetime.tzinfo): 
    def __init__(self, offset): 
        self._offset = offset 
        seconds = abs(offset).total_seconds() 
        self._name = 'UTC%s%02d:%02d' % ( 
            '-' if offset.days < 0 else '+', 
            seconds // 3600, 
            seconds % 3600 // 60 
        ) 
 
    def tzname(self, dt=None): 
        return self._name 
 
    def utcoffset(self, dt=None): 
        return self._offset 
 
    def dst(self, dt=None): 
        return datetime.timedelta(0) 
 
    def __copy__(self): 
        return self.__deepcopy__() 
 
    def __deepcopy__(self, memodict={}): 
        return self.__class__(self.utcoffset()) 
 
    __repr__ = __str__ = tzname 
 
 
class BaseConstructor(object):

    yaml_constructors = {}
    yaml_multi_constructors = {}

    def __init__(self):
        self.constructed_objects = {}
        self.recursive_objects = {}
        self.state_generators = []
        self.deep_construct = False

    def check_data(self):
        # If there are more documents available?
        return self.check_node()

    def check_state_key(self, key): 
        """Block special attributes/methods from being set in a newly created 
        object, to prevent user-controlled methods from being called during 
        deserialization""" 
        if self.get_state_keys_blacklist_regexp().match(key): 
            raise ConstructorError(None, None, 
                "blacklisted key '%s' in instance state found" % (key,), None) 
 
    def get_data(self):
        # Construct and return the next document.
        if self.check_node():
            return self.construct_document(self.get_node())

    def get_single_data(self):
        # Ensure that the stream contains a single document and construct it.
        node = self.get_single_node()
        if node is not None:
            return self.construct_document(node)
        return None

    def construct_document(self, node):
        data = self.construct_object(node)
        while self.state_generators:
            state_generators = self.state_generators
            self.state_generators = []
            for generator in state_generators:
                for dummy in generator:
                    pass
        self.constructed_objects = {}
        self.recursive_objects = {}
        self.deep_construct = False
        return data

    def construct_object(self, node, deep=False):
        if node in self.constructed_objects:
            return self.constructed_objects[node]
        if deep:
            old_deep = self.deep_construct
            self.deep_construct = True
        if node in self.recursive_objects:
            raise ConstructorError(None, None,
                    "found unconstructable recursive node", node.start_mark)
        self.recursive_objects[node] = None
        constructor = None
        tag_suffix = None
        if node.tag in self.yaml_constructors:
            constructor = self.yaml_constructors[node.tag]
        else:
            for tag_prefix in self.yaml_multi_constructors:
                if tag_prefix is not None and node.tag.startswith(tag_prefix): 
                    tag_suffix = node.tag[len(tag_prefix):]
                    constructor = self.yaml_multi_constructors[tag_prefix]
                    break
            else:
                if None in self.yaml_multi_constructors:
                    tag_suffix = node.tag
                    constructor = self.yaml_multi_constructors[None]
                elif None in self.yaml_constructors:
                    constructor = self.yaml_constructors[None]
                elif isinstance(node, ScalarNode):
                    constructor = self.__class__.construct_scalar
                elif isinstance(node, SequenceNode):
                    constructor = self.__class__.construct_sequence
                elif isinstance(node, MappingNode):
                    constructor = self.__class__.construct_mapping
        if tag_suffix is None:
            data = constructor(self, node)
        else:
            data = constructor(self, tag_suffix, node)
        if isinstance(data, types.GeneratorType):
            generator = data
            data = generator.next()
            if self.deep_construct:
                for dummy in generator:
                    pass
            else:
                self.state_generators.append(generator)
        self.constructed_objects[node] = data
        del self.recursive_objects[node]
        if deep:
            self.deep_construct = old_deep
        return data

    def construct_scalar(self, node):
        if not isinstance(node, ScalarNode):
            raise ConstructorError(None, None,
                    "expected a scalar node, but found %s" % node.id,
                    node.start_mark)
        return node.value

    def construct_sequence(self, node, deep=False):
        if not isinstance(node, SequenceNode):
            raise ConstructorError(None, None,
                    "expected a sequence node, but found %s" % node.id,
                    node.start_mark)
        return [self.construct_object(child, deep=deep)
                for child in node.value]

    def construct_mapping(self, node, deep=False):
        if not isinstance(node, MappingNode):
            raise ConstructorError(None, None,
                    "expected a mapping node, but found %s" % node.id,
                    node.start_mark)
        mapping = {}
        for key_node, value_node in node.value:
            key = self.construct_object(key_node, deep=deep)
            try:
                hash(key)
            except TypeError, exc:
                raise ConstructorError("while constructing a mapping", node.start_mark,
                        "found unacceptable key (%s)" % exc, key_node.start_mark)
            value = self.construct_object(value_node, deep=deep)
            mapping[key] = value
        return mapping

    def construct_pairs(self, node, deep=False):
        if not isinstance(node, MappingNode):
            raise ConstructorError(None, None,
                    "expected a mapping node, but found %s" % node.id,
                    node.start_mark)
        pairs = []
        for key_node, value_node in node.value:
            key = self.construct_object(key_node, deep=deep)
            value = self.construct_object(value_node, deep=deep)
            pairs.append((key, value))
        return pairs

    def add_constructor(cls, tag, constructor):
        if not 'yaml_constructors' in cls.__dict__:
            cls.yaml_constructors = cls.yaml_constructors.copy()
        cls.yaml_constructors[tag] = constructor
    add_constructor = classmethod(add_constructor)

    def add_multi_constructor(cls, tag_prefix, multi_constructor):
        if not 'yaml_multi_constructors' in cls.__dict__:
            cls.yaml_multi_constructors = cls.yaml_multi_constructors.copy()
        cls.yaml_multi_constructors[tag_prefix] = multi_constructor
    add_multi_constructor = classmethod(add_multi_constructor)

class SafeConstructor(BaseConstructor):

    def construct_scalar(self, node):
        if isinstance(node, MappingNode):
            for key_node, value_node in node.value:
                if key_node.tag == u'tag:yaml.org,2002:value':
                    return self.construct_scalar(value_node)
        return BaseConstructor.construct_scalar(self, node)

    def flatten_mapping(self, node):
        merge = []
        index = 0
        while index < len(node.value):
            key_node, value_node = node.value[index]
            if key_node.tag == u'tag:yaml.org,2002:merge':
                del node.value[index]
                if isinstance(value_node, MappingNode):
                    self.flatten_mapping(value_node)
                    merge.extend(value_node.value)
                elif isinstance(value_node, SequenceNode):
                    submerge = []
                    for subnode in value_node.value:
                        if not isinstance(subnode, MappingNode):
                            raise ConstructorError("while constructing a mapping",
                                    node.start_mark,
                                    "expected a mapping for merging, but found %s"
                                    % subnode.id, subnode.start_mark)
                        self.flatten_mapping(subnode)
                        submerge.append(subnode.value)
                    submerge.reverse()
                    for value in submerge:
                        merge.extend(value)
                else:
                    raise ConstructorError("while constructing a mapping", node.start_mark,
                            "expected a mapping or list of mappings for merging, but found %s"
                            % value_node.id, value_node.start_mark)
            elif key_node.tag == u'tag:yaml.org,2002:value':
                key_node.tag = u'tag:yaml.org,2002:str'
                index += 1
            else:
                index += 1
        if merge:
            node.value = merge + node.value

    def construct_mapping(self, node, deep=False):
        if isinstance(node, MappingNode):
            self.flatten_mapping(node)
        return BaseConstructor.construct_mapping(self, node, deep=deep)

    def construct_yaml_null(self, node):
        self.construct_scalar(node)
        return None

    bool_values = {
        u'yes':     True,
        u'no':      False,
        u'true':    True,
        u'false':   False,
        u'on':      True,
        u'off':     False,
    }

    def construct_yaml_bool(self, node):
        value = self.construct_scalar(node)
        return self.bool_values[value.lower()]

    def construct_yaml_int(self, node):
        value = str(self.construct_scalar(node))
        value = value.replace('_', '')
        sign = +1
        if value[0] == '-':
            sign = -1
        if value[0] in '+-':
            value = value[1:]
        if value == '0':
            return 0
        elif value.startswith('0b'):
            return sign*int(value[2:], 2)
        elif value.startswith('0x'):
            return sign*int(value[2:], 16)
        elif value[0] == '0':
            return sign*int(value, 8)
        elif ':' in value:
            digits = [int(part) for part in value.split(':')]
            digits.reverse()
            base = 1
            value = 0
            for digit in digits:
                value += digit*base
                base *= 60
            return sign*value
        else:
            return sign*int(value)

    inf_value = 1e300
    while inf_value != inf_value*inf_value:
        inf_value *= inf_value
    nan_value = -inf_value/inf_value   # Trying to make a quiet NaN (like C99).

    def construct_yaml_float(self, node):
        value = str(self.construct_scalar(node))
        value = value.replace('_', '').lower()
        sign = +1
        if value[0] == '-':
            sign = -1
        if value[0] in '+-':
            value = value[1:]
        if value == '.inf':
            return sign*self.inf_value
        elif value == '.nan':
            return self.nan_value
        elif ':' in value:
            digits = [float(part) for part in value.split(':')]
            digits.reverse()
            base = 1
            value = 0.0
            for digit in digits:
                value += digit*base
                base *= 60
            return sign*value
        else:
            return sign*float(value)

    def construct_yaml_binary(self, node):
        value = self.construct_scalar(node)
        try:
            return str(value).decode('base64')
        except (binascii.Error, UnicodeEncodeError), exc:
            raise ConstructorError(None, None,
                    "failed to decode base64 data: %s" % exc, node.start_mark) 

    timestamp_regexp = re.compile(
            ur'''^(?P<year>[0-9][0-9][0-9][0-9])
                -(?P<month>[0-9][0-9]?)
                -(?P<day>[0-9][0-9]?)
                (?:(?:[Tt]|[ \t]+)
                (?P<hour>[0-9][0-9]?)
                :(?P<minute>[0-9][0-9])
                :(?P<second>[0-9][0-9])
                (?:\.(?P<fraction>[0-9]*))?
                (?:[ \t]*(?P<tz>Z|(?P<tz_sign>[-+])(?P<tz_hour>[0-9][0-9]?)
                (?::(?P<tz_minute>[0-9][0-9]))?))?)?$''', re.X)

    def construct_yaml_timestamp(self, node):
        value = self.construct_scalar(node)
        match = self.timestamp_regexp.match(node.value)
        values = match.groupdict()
        year = int(values['year'])
        month = int(values['month'])
        day = int(values['day'])
        if not values['hour']:
            return datetime.date(year, month, day)
        hour = int(values['hour'])
        minute = int(values['minute'])
        second = int(values['second'])
        fraction = 0
        tzinfo = None 
        if values['fraction']:
            fraction = values['fraction'][:6]
            while len(fraction) < 6:
                fraction += '0'
            fraction = int(fraction)
        if values['tz_sign']:
            tz_hour = int(values['tz_hour'])
            tz_minute = int(values['tz_minute'] or 0)
            delta = datetime.timedelta(hours=tz_hour, minutes=tz_minute)
            if values['tz_sign'] == '-':
                delta = -delta
            tzinfo = timezone(delta) 
        elif values['tz']: 
            tzinfo = timezone(datetime.timedelta(0)) 
        return datetime.datetime(year, month, day, hour, minute, second, fraction, 
                                 tzinfo=tzinfo) 

    def construct_yaml_omap(self, node):
        # Note: we do not check for duplicate keys, because it's too
        # CPU-expensive.
        omap = []
        yield omap
        if not isinstance(node, SequenceNode):
            raise ConstructorError("while constructing an ordered map", node.start_mark,
                    "expected a sequence, but found %s" % node.id, node.start_mark)
        for subnode in node.value:
            if not isinstance(subnode, MappingNode):
                raise ConstructorError("while constructing an ordered map", node.start_mark,
                        "expected a mapping of length 1, but found %s" % subnode.id,
                        subnode.start_mark)
            if len(subnode.value) != 1:
                raise ConstructorError("while constructing an ordered map", node.start_mark,
                        "expected a single mapping item, but found %d items" % len(subnode.value),
                        subnode.start_mark)
            key_node, value_node = subnode.value[0]
            key = self.construct_object(key_node)
            value = self.construct_object(value_node)
            omap.append((key, value))

    def construct_yaml_pairs(self, node):
        # Note: the same code as `construct_yaml_omap`.
        pairs = []
        yield pairs
        if not isinstance(node, SequenceNode):
            raise ConstructorError("while constructing pairs", node.start_mark,
                    "expected a sequence, but found %s" % node.id, node.start_mark)
        for subnode in node.value:
            if not isinstance(subnode, MappingNode):
                raise ConstructorError("while constructing pairs", node.start_mark,
                        "expected a mapping of length 1, but found %s" % subnode.id,
                        subnode.start_mark)
            if len(subnode.value) != 1:
                raise ConstructorError("while constructing pairs", node.start_mark,
                        "expected a single mapping item, but found %d items" % len(subnode.value),
                        subnode.start_mark)
            key_node, value_node = subnode.value[0]
            key = self.construct_object(key_node)
            value = self.construct_object(value_node)
            pairs.append((key, value))

    def construct_yaml_set(self, node):
        data = set()
        yield data
        value = self.construct_mapping(node)
        data.update(value)

    def construct_yaml_str(self, node):
        value = self.construct_scalar(node)
        try:
            return value.encode('ascii')
        except UnicodeEncodeError:
            return value

    def construct_yaml_seq(self, node):
        data = []
        yield data
        data.extend(self.construct_sequence(node))

    def construct_yaml_map(self, node):
        data = {}
        yield data
        value = self.construct_mapping(node)
        data.update(value)

    def construct_yaml_object(self, node, cls):
        data = cls.__new__(cls)
        yield data
        if hasattr(data, '__setstate__'):
            state = self.construct_mapping(node, deep=True)
            data.__setstate__(state)
        else:
            state = self.construct_mapping(node)
            data.__dict__.update(state)

    def construct_undefined(self, node):
        raise ConstructorError(None, None,
                "could not determine a constructor for the tag %r" % node.tag.encode('utf-8'),
                node.start_mark)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:null',
        SafeConstructor.construct_yaml_null)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:bool',
        SafeConstructor.construct_yaml_bool)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:int',
        SafeConstructor.construct_yaml_int)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:float',
        SafeConstructor.construct_yaml_float)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:binary',
        SafeConstructor.construct_yaml_binary)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:timestamp',
        SafeConstructor.construct_yaml_timestamp)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:omap',
        SafeConstructor.construct_yaml_omap)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:pairs',
        SafeConstructor.construct_yaml_pairs)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:set',
        SafeConstructor.construct_yaml_set)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:str',
        SafeConstructor.construct_yaml_str)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:seq',
        SafeConstructor.construct_yaml_seq)

SafeConstructor.add_constructor(
        u'tag:yaml.org,2002:map',
        SafeConstructor.construct_yaml_map)

SafeConstructor.add_constructor(None,
        SafeConstructor.construct_undefined)

class FullConstructor(SafeConstructor): 
    # 'extend' is blacklisted because it is used by 
    # construct_python_object_apply to add `listitems` to a newly generate 
    # python instance 
    def get_state_keys_blacklist(self): 
        return ['^extend$', '^__.*__$'] 

    def get_state_keys_blacklist_regexp(self): 
        if not hasattr(self, 'state_keys_blacklist_regexp'): 
            self.state_keys_blacklist_regexp = re.compile('(' + '|'.join(self.get_state_keys_blacklist()) + ')') 
        return self.state_keys_blacklist_regexp 
 
    def construct_python_str(self, node):
        return self.construct_scalar(node).encode('utf-8')

    def construct_python_unicode(self, node):
        return self.construct_scalar(node)

    def construct_python_long(self, node):
        return long(self.construct_yaml_int(node))

    def construct_python_complex(self, node):
       return complex(self.construct_scalar(node))

    def construct_python_tuple(self, node):
        return tuple(self.construct_sequence(node))

    def find_python_module(self, name, mark, unsafe=False): 
        if not name:
            raise ConstructorError("while constructing a Python module", mark,
                    "expected non-empty name appended to the tag", mark)
        if unsafe: 
            try: 
                __import__(name) 
            except ImportError, exc: 
                raise ConstructorError("while constructing a Python module", mark, 
                        "cannot find module %r (%s)" % (name.encode('utf-8'), exc), mark) 
        if name not in sys.modules: 
            raise ConstructorError("while constructing a Python module", mark,
                    "module %r is not imported" % name.encode('utf-8'), mark) 
        return sys.modules[name]

    def find_python_name(self, name, mark, unsafe=False): 
        if not name:
            raise ConstructorError("while constructing a Python object", mark,
                    "expected non-empty name appended to the tag", mark)
        if u'.' in name:
            module_name, object_name = name.rsplit('.', 1)
        else:
            module_name = '__builtin__'
            object_name = name
        if unsafe: 
            try: 
                __import__(module_name) 
            except ImportError, exc: 
                raise ConstructorError("while constructing a Python object", mark, 
                        "cannot find module %r (%s)" % (module_name.encode('utf-8'), exc), mark) 
        if module_name not in sys.modules: 
            raise ConstructorError("while constructing a Python object", mark,
                    "module %r is not imported" % module_name.encode('utf-8'), mark) 
        module = sys.modules[module_name]
        if not hasattr(module, object_name):
            raise ConstructorError("while constructing a Python object", mark,
                    "cannot find %r in the module %r" % (object_name.encode('utf-8'),
                        module.__name__), mark)
        return getattr(module, object_name)

    def construct_python_name(self, suffix, node):
        value = self.construct_scalar(node)
        if value:
            raise ConstructorError("while constructing a Python name", node.start_mark,
                    "expected the empty value, but found %r" % value.encode('utf-8'),
                    node.start_mark)
        return self.find_python_name(suffix, node.start_mark)

    def construct_python_module(self, suffix, node):
        value = self.construct_scalar(node)
        if value:
            raise ConstructorError("while constructing a Python module", node.start_mark,
                    "expected the empty value, but found %r" % value.encode('utf-8'),
                    node.start_mark)
        return self.find_python_module(suffix, node.start_mark)

    class classobj: pass

    def make_python_instance(self, suffix, node,
            args=None, kwds=None, newobj=False, unsafe=False): 
        if not args:
            args = []
        if not kwds:
            kwds = {}
        cls = self.find_python_name(suffix, node.start_mark)
        if not (unsafe or isinstance(cls, type) or isinstance(cls, type(self.classobj))): 
            raise ConstructorError("while constructing a Python instance", node.start_mark, 
                    "expected a class, but found %r" % type(cls), 
                    node.start_mark) 
        if newobj and isinstance(cls, type(self.classobj))  \
                and not args and not kwds:
            instance = self.classobj()
            instance.__class__ = cls
            return instance
        elif newobj and isinstance(cls, type):
            return cls.__new__(cls, *args, **kwds)
        else:
            return cls(*args, **kwds)

    def set_python_instance_state(self, instance, state, unsafe=False): 
        if hasattr(instance, '__setstate__'):
            instance.__setstate__(state)
        else:
            slotstate = {}
            if isinstance(state, tuple) and len(state) == 2:
                state, slotstate = state
            if hasattr(instance, '__dict__'):
                if not unsafe and state: 
                    for key in state.keys(): 
                        self.check_state_key(key) 
                instance.__dict__.update(state)
            elif state:
                slotstate.update(state)
            for key, value in slotstate.items():
                if not unsafe: 
                    self.check_state_key(key) 
                setattr(instance, key, value) 

    def construct_python_object(self, suffix, node):
        # Format:
        #   !!python/object:module.name { ... state ... }
        instance = self.make_python_instance(suffix, node, newobj=True)
        yield instance
        deep = hasattr(instance, '__setstate__')
        state = self.construct_mapping(node, deep=deep)
        self.set_python_instance_state(instance, state)

    def construct_python_object_apply(self, suffix, node, newobj=False):
        # Format:
        #   !!python/object/apply       # (or !!python/object/new)
        #   args: [ ... arguments ... ]
        #   kwds: { ... keywords ... }
        #   state: ... state ...
        #   listitems: [ ... listitems ... ]
        #   dictitems: { ... dictitems ... }
        # or short format:
        #   !!python/object/apply [ ... arguments ... ]
        # The difference between !!python/object/apply and !!python/object/new
        # is how an object is created, check make_python_instance for details.
        if isinstance(node, SequenceNode):
            args = self.construct_sequence(node, deep=True)
            kwds = {}
            state = {}
            listitems = []
            dictitems = {}
        else:
            value = self.construct_mapping(node, deep=True)
            args = value.get('args', [])
            kwds = value.get('kwds', {})
            state = value.get('state', {})
            listitems = value.get('listitems', [])
            dictitems = value.get('dictitems', {})
        instance = self.make_python_instance(suffix, node, args, kwds, newobj)
        if state:
            self.set_python_instance_state(instance, state)
        if listitems:
            instance.extend(listitems)
        if dictitems:
            for key in dictitems:
                instance[key] = dictitems[key]
        return instance

    def construct_python_object_new(self, suffix, node):
        return self.construct_python_object_apply(suffix, node, newobj=True)

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/none',
    FullConstructor.construct_yaml_null) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/bool',
    FullConstructor.construct_yaml_bool) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/str',
    FullConstructor.construct_python_str) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/unicode',
    FullConstructor.construct_python_unicode) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/int',
    FullConstructor.construct_yaml_int) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/long',
    FullConstructor.construct_python_long) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/float',
    FullConstructor.construct_yaml_float) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/complex',
    FullConstructor.construct_python_complex) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/list',
    FullConstructor.construct_yaml_seq) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/tuple',
    FullConstructor.construct_python_tuple) 

FullConstructor.add_constructor( 
    u'tag:yaml.org,2002:python/dict',
    FullConstructor.construct_yaml_map) 

FullConstructor.add_multi_constructor( 
    u'tag:yaml.org,2002:python/name:',
    FullConstructor.construct_python_name) 

class UnsafeConstructor(FullConstructor): 
 
    def find_python_module(self, name, mark): 
        return super(UnsafeConstructor, self).find_python_module(name, mark, unsafe=True) 
 
    def find_python_name(self, name, mark): 
        return super(UnsafeConstructor, self).find_python_name(name, mark, unsafe=True) 
 
    def make_python_instance(self, suffix, node, args=None, kwds=None, newobj=False): 
        return super(UnsafeConstructor, self).make_python_instance( 
            suffix, node, args, kwds, newobj, unsafe=True) 
 
    def set_python_instance_state(self, instance, state): 
        return super(UnsafeConstructor, self).set_python_instance_state( 
            instance, state, unsafe=True) 
 
UnsafeConstructor.add_multi_constructor( 
    u'tag:yaml.org,2002:python/module:', 
    UnsafeConstructor.construct_python_module) 
 
UnsafeConstructor.add_multi_constructor( 
    u'tag:yaml.org,2002:python/object:', 
    UnsafeConstructor.construct_python_object) 
 
UnsafeConstructor.add_multi_constructor( 
    u'tag:yaml.org,2002:python/object/new:', 
    UnsafeConstructor.construct_python_object_new) 
 
UnsafeConstructor.add_multi_constructor( 
    u'tag:yaml.org,2002:python/object/apply:', 
    UnsafeConstructor.construct_python_object_apply) 
 
# Constructor is same as UnsafeConstructor. Need to leave this in place in case 
# people have extended it directly. 
class Constructor(UnsafeConstructor): 
    pass