  
  from io import BytesIO
  
  from django.core import validators
  from django.core.exceptions import ObjectDoesNotExist, ValidationError
  from django.core.urlresolvers import resolve, get_script_prefix
  from django.conf import settings
  from django import forms
  from django.forms import widgets
  from django.forms.models import ModelChoiceIterator
  from django.utils.encoding import is_protected_type, smart_unicode
 
</s> remove from django.forms.models import ModelChoiceIterator
 </s> add  </s> remove from rest_framework.reverse import reverse
 </s> add  </s> remove from urlparse import urlparse
 </s> add  </s> remove 
 </s> add from rest_framework.relations import * </s> remove ##### Relational fields #####


# Not actually Writable, but subclasses may need to be.
class RelatedField(WritableField):
    """
    Base class for related model fields.

    If not overridden, this represents a to-one relationship, using the unicode
    representation of the target.
    """
    widget = widgets.Select
    cache_choices = False
    empty_label = None
    default_read_only = True  # TODO: Remove this

    def __init__(self, *args, **kwargs):
        self.queryset = kwargs.pop('queryset', None)
        self.null = kwargs.pop('null', False)
        super(RelatedField, self).__init__(*args, **kwargs)
        self.read_only = kwargs.pop('read_only', self.default_read_only)

    def initialize(self, parent, field_name):
        super(RelatedField, self).initialize(parent, field_name)
        if self.queryset is None and not self.read_only:
            try:
                manager = getattr(self.parent.opts.model, self.source or field_name)
                if hasattr(manager, 'related'):  # Forward
                    self.queryset = manager.related.model._default_manager.all()
                else:  # Reverse
                    self.queryset = manager.field.rel.to._default_manager.all()
            except:
                raise
                msg = ('Serializer related fields must include a `queryset`' +
                       ' argument or set `read_only=True')
                raise Exception(msg)

    ### We need this stuff to make form choices work...

    # def __deepcopy__(self, memo):
    #     result = super(RelatedField, self).__deepcopy__(memo)
    #     result.queryset = result.queryset
    #     return result

    def prepare_value(self, obj):
        return self.to_native(obj)

    def label_from_instance(self, obj):
        """
        Return a readable representation for use with eg. select widgets.
        """
        desc = smart_unicode(obj)
        ident = smart_unicode(self.to_native(obj))
        if desc == ident:
            return desc
        return "%s - %s" % (desc, ident)

    def _get_queryset(self):
        return self._queryset

    def _set_queryset(self, queryset):
        self._queryset = queryset
        self.widget.choices = self.choices

    queryset = property(_get_queryset, _set_queryset)

    def _get_choices(self):
        # If self._choices is set, then somebody must have manually set
        # the property self.choices. In this case, just return self._choices.
        if hasattr(self, '_choices'):
            return self._choices

        # Otherwise, execute the QuerySet in self.queryset to determine the
        # choices dynamically. Return a fresh ModelChoiceIterator that has not been
        # consumed. Note that we're instantiating a new ModelChoiceIterator *each*
        # time _get_choices() is called (and, thus, each time self.choices is
        # accessed) so that we can ensure the QuerySet has not been consumed. This
        # construct might look complicated but it allows for lazy evaluation of
        # the queryset.
        return ModelChoiceIterator(self)

    def _set_choices(self, value):
        # Setting choices also sets the choices on the widget.
        # choices can be any iterable, but we call list() on it because
        # it will be consumed more than once.
        self._choices = self.widget.choices = list(value)

    choices = property(_get_choices, _set_choices)

    ### Regular serializer stuff...

    def field_to_native(self, obj, field_name):
        value = getattr(obj, self.source or field_name)
        return self.to_native(value)

    def field_from_native(self, data, files, field_name, into):
        if self.read_only:
            return

        try:
            value = data[field_name]
        except KeyError:
            if self.required:
                raise ValidationError(self.error_messages['required'])
            return

        if value in (None, '') and not self.null:
            raise ValidationError('Value may not be null')
        elif value in (None, '') and self.null:
            into[(self.source or field_name)] = None
        else:
            into[(self.source or field_name)] = self.from_native(value)


class ManyRelatedMixin(object):
    """
    Mixin to convert a related field to a many related field.
    """
    widget = widgets.SelectMultiple

    def field_to_native(self, obj, field_name):
        value = getattr(obj, self.source or field_name)
        return [self.to_native(item) for item in value.all()]

    def field_from_native(self, data, files, field_name, into):
        if self.read_only:
            return

        try:
            # Form data
            value = data.getlist(self.source or field_name)
        except:
            # Non-form data
            value = data.get(self.source or field_name)
        else:
            if value == ['']:
                value = []

        into[field_name] = [self.from_native(item) for item in value]


class ManyRelatedField(ManyRelatedMixin, RelatedField):
    """
    Base class for related model managers.

    If not overridden, this represents a to-many relationship, using the unicode
    representations of the target, and is read-only.
    """
    pass


### PrimaryKey relationships

class PrimaryKeyRelatedField(RelatedField):
    """
    Represents a to-one relationship as a pk value.
    """
    default_read_only = False
    form_field_class = forms.ChoiceField

    # TODO: Remove these field hacks...
    def prepare_value(self, obj):
        return self.to_native(obj.pk)

    def label_from_instance(self, obj):
        """
        Return a readable representation for use with eg. select widgets.
        """
        desc = smart_unicode(obj)
        ident = smart_unicode(self.to_native(obj.pk))
        if desc == ident:
            return desc
        return "%s - %s" % (desc, ident)

    # TODO: Possibly change this to just take `obj`, through prob less performant
    def to_native(self, pk):
        return pk

    def from_native(self, data):
        if self.queryset is None:
            raise Exception('Writable related fields must include a `queryset` argument')

        try:
            return self.queryset.get(pk=data)
        except ObjectDoesNotExist:
            msg = "Invalid pk '%s' - object does not exist." % smart_unicode(data)
            raise ValidationError(msg)

    def field_to_native(self, obj, field_name):
        try:
            # Prefer obj.serializable_value for performance reasons
            pk = obj.serializable_value(self.source or field_name)
        except AttributeError:
            # RelatedObject (reverse relationship)
            obj = getattr(obj, self.source or field_name)
            return self.to_native(obj.pk)
        # Forward relationship
        return self.to_native(pk)


class ManyPrimaryKeyRelatedField(ManyRelatedField):
    """
    Represents a to-many relationship as a pk value.
    """
    default_read_only = False
    form_field_class = forms.MultipleChoiceField

    def prepare_value(self, obj):
        return self.to_native(obj.pk)

    def label_from_instance(self, obj):
        """
        Return a readable representation for use with eg. select widgets.
        """
        desc = smart_unicode(obj)
        ident = smart_unicode(self.to_native(obj.pk))
        if desc == ident:
            return desc
        return "%s - %s" % (desc, ident)

    def to_native(self, pk):
        return pk

    def field_to_native(self, obj, field_name):
        try:
            # Prefer obj.serializable_value for performance reasons
            queryset = obj.serializable_value(self.source or field_name)
        except AttributeError:
            # RelatedManager (reverse relationship)
            queryset = getattr(obj, self.source or field_name)
            return [self.to_native(item.pk) for item in queryset.all()]
        # Forward relationship
        return [self.to_native(item.pk) for item in queryset.all()]

    def from_native(self, data):
        if self.queryset is None:
            raise Exception('Writable related fields must include a `queryset` argument')

        try:
            return self.queryset.get(pk=data)
        except ObjectDoesNotExist:
            msg = "Invalid pk '%s' - object does not exist." % smart_unicode(data)
            raise ValidationError(msg)

### Slug relationships


class SlugRelatedField(RelatedField):
    default_read_only = False
    form_field_class = forms.ChoiceField

    def __init__(self, *args, **kwargs):
        self.slug_field = kwargs.pop('slug_field', None)
        assert self.slug_field, 'slug_field is required'
        super(SlugRelatedField, self).__init__(*args, **kwargs)

    def to_native(self, obj):
        return getattr(obj, self.slug_field)

    def from_native(self, data):
        if self.queryset is None:
            raise Exception('Writable related fields must include a `queryset` argument')

        try:
            return self.queryset.get(**{self.slug_field: data})
        except ObjectDoesNotExist:
            raise ValidationError('Object with %s=%s does not exist.' %
                                  (self.slug_field, unicode(data)))


class ManySlugRelatedField(ManyRelatedMixin, SlugRelatedField):
    form_field_class = forms.MultipleChoiceField


### Hyperlinked relationships

class HyperlinkedRelatedField(RelatedField):
    """
    Represents a to-one relationship, using hyperlinking.
    """
    pk_url_kwarg = 'pk'
    slug_field = 'slug'
    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden
    default_read_only = False
    form_field_class = forms.ChoiceField

    def __init__(self, *args, **kwargs):
        try:
            self.view_name = kwargs.pop('view_name')
        except:
            raise ValueError("Hyperlinked field requires 'view_name' kwarg")

        self.slug_field = kwargs.pop('slug_field', self.slug_field)
        default_slug_kwarg = self.slug_url_kwarg or self.slug_field
        self.pk_url_kwarg = kwargs.pop('pk_url_kwarg', self.pk_url_kwarg)
        self.slug_url_kwarg = kwargs.pop('slug_url_kwarg', default_slug_kwarg)

        self.format = kwargs.pop('format', None)
        super(HyperlinkedRelatedField, self).__init__(*args, **kwargs)

    def get_slug_field(self):
        """
        Get the name of a slug field to be used to look up by slug.
        """
        return self.slug_field

    def to_native(self, obj):
        view_name = self.view_name
        request = self.context.get('request', None)
        format = self.format or self.context.get('format', None)
        pk = getattr(obj, 'pk', None)
        if pk is None:
            return
        kwargs = {self.pk_url_kwarg: pk}
        try:
            return reverse(view_name, kwargs=kwargs, request=request, format=format)
        except:
            pass

        slug = getattr(obj, self.slug_field, None)

        if not slug:
            raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)

        kwargs = {self.slug_url_kwarg: slug}
        try:
            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
        except:
            pass

        kwargs = {self.pk_url_kwarg: obj.pk, self.slug_url_kwarg: slug}
        try:
            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
        except:
            pass

        raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)

    def from_native(self, value):
        # Convert URL -> model instance pk
        # TODO: Use values_list
        if self.queryset is None:
            raise Exception('Writable related fields must include a `queryset` argument')

        if value.startswith('http:') or value.startswith('https:'):
            # If needed convert absolute URLs to relative path
            value = urlparse(value).path
            prefix = get_script_prefix()
            if value.startswith(prefix):
                value = '/' + value[len(prefix):]

        try:
            match = resolve(value)
        except:
            raise ValidationError('Invalid hyperlink - No URL match')

        if match.url_name != self.view_name:
            raise ValidationError('Invalid hyperlink - Incorrect URL match')

        pk = match.kwargs.get(self.pk_url_kwarg, None)
        slug = match.kwargs.get(self.slug_url_kwarg, None)

        # Try explicit primary key.
        if pk is not None:
            queryset = self.queryset.filter(pk=pk)
        # Next, try looking up by slug.
        elif slug is not None:
            slug_field = self.get_slug_field()
            queryset = self.queryset.filter(**{slug_field: slug})
        # If none of those are defined, it's an error.
        else:
            raise ValidationError('Invalid hyperlink')

        try:
            obj = queryset.get()
        except ObjectDoesNotExist:
            raise ValidationError('Invalid hyperlink - object does not exist.')
        return obj


class ManyHyperlinkedRelatedField(ManyRelatedMixin, HyperlinkedRelatedField):
    """
    Represents a to-many relationship, using hyperlinking.
    """
    form_field_class = forms.MultipleChoiceField


class HyperlinkedIdentityField(Field):
    """
    Represents the instance, or a property on the instance, using hyperlinking.
    """
    pk_url_kwarg = 'pk'
    slug_field = 'slug'
    slug_url_kwarg = None  # Defaults to same as `slug_field` unless overridden

    def __init__(self, *args, **kwargs):
        # TODO: Make view_name mandatory, and have the
        # HyperlinkedModelSerializer set it on-the-fly
        self.view_name = kwargs.pop('view_name', None)
        self.format = kwargs.pop('format', None)

        self.slug_field = kwargs.pop('slug_field', self.slug_field)
        default_slug_kwarg = self.slug_url_kwarg or self.slug_field
        self.pk_url_kwarg = kwargs.pop('pk_url_kwarg', self.pk_url_kwarg)
        self.slug_url_kwarg = kwargs.pop('slug_url_kwarg', default_slug_kwarg)

        super(HyperlinkedIdentityField, self).__init__(*args, **kwargs)

    def field_to_native(self, obj, field_name):
        request = self.context.get('request', None)
        format = self.format or self.context.get('format', None)
        view_name = self.view_name or self.parent.opts.view_name
        kwargs = {self.pk_url_kwarg: obj.pk}
        try:
            return reverse(view_name, kwargs=kwargs, request=request, format=format)
        except:
            pass

        slug = getattr(obj, self.slug_field, None)

        if not slug:
            raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)

        kwargs = {self.slug_url_kwarg: slug}
        try:
            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
        except:
            pass

        kwargs = {self.pk_url_kwarg: obj.pk, self.slug_url_kwarg: slug}
        try:
            return reverse(self.view_name, kwargs=kwargs, request=request, format=format)
        except:
            pass

        raise ValidationError('Could not resolve URL for field using view name "%s"' % view_name)

 </s> add 
from django.core.exceptions import ValidationError
  
  from io import BytesIO
  
  from django.core import validators
from django.core.exceptions import ValidationError
from django.core.exceptions import ValidationError
  from django.conf import settings
  from django import forms
  from django.forms import widgets
  from django.forms.models import ModelChoiceIterator
  from django.utils.encoding import is_protected_type, smart_unicode
keep keep keep keep replace replace keep keep keep keep keep
 Relation fields move into relations.py 
rest_framework/fields.py