django-rest-framework/rest_framework/fields.py

from __future__ import unicode_literals
import six

import copy
import datetime
import inspect
import re
import warnings

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.forms import widgets
from django.forms.models import ModelChoiceIterator
from django.utils.encoding import is_protected_type
try:
    from django.utils.encoding import smart_text
except ImportError:
    from django.utils.encoding import smart_unicode as smart_text
from django.utils.translation import ugettext_lazy as _
from rest_framework.reverse import reverse
from rest_framework.compat import parse_date, parse_datetime
from rest_framework.compat import timezone
try:
    from urllib.parse import urlparse
except ImportError:
    from urlparse import urlparse


def is_simple_callable(obj):
    """
    True if the object is a callable that takes no arguments.
    """
    return (
        (inspect.isfunction(obj) and not inspect.getargspec(obj)[0]) or
        (inspect.ismethod(obj) and len(inspect.getargspec(obj)[0]) <= 1)
    )


class Field(object):
    creation_counter = 0
    empty = ''
    type_name = None
    _use_files = None

    def __init__(self, source=None):
        self.parent = None

        self.creation_counter = Field.creation_counter
        Field.creation_counter += 1

        self.source = source

    def initialize(self, parent, field_name):
        """
        Called to set up a field prior to field_to_native or field_from_native.

        parent - The parent serializer.
        model_field - The model field this field corresponds to, if one exists.
        """
        self.parent = parent
        self.root = parent.root or parent
        self.context = self.root.context

    def field_from_native(self, data, files, field_name, into):
        """
        Given a dictionary and a field name, updates the dictionary `into`,
        with the field and it's deserialized value.
        """
        return

    def field_to_native(self, obj, field_name):
        """
        Given and object and a field name, returns the value that should be
        serialized for that field.
        """
        if obj is None:
            return self.empty

        if self.source == '*':
            return self.to_native(obj)

        if self.source:
            value = obj
            for component in self.source.split('.'):
                value = getattr(value, component)
                if is_simple_callable(value):
                    value = value()
        else:
            value = getattr(obj, field_name)
        return self.to_native(value)

    def to_native(self, value):
        """
        Converts the field's value into it's simple representation.
        """
        if is_simple_callable(value):
            value = value()

        if is_protected_type(value):
            return value
        elif hasattr(value, '__iter__') and not isinstance(value, (dict, six.string_types)):
            return [self.to_native(item) for item in value]
        elif isinstance(value, dict):
            return dict(map(self.to_native, (k, v)) for k, v in value.items())
        return smart_text(value)

    def attributes(self):
        """
        Returns a dictionary of attributes to be used when serializing to xml.
        """
        if self.type_name:
            return {'type': self.type_name}
        return {}


class WritableField(Field):
    """
    Base for read/write fields.
    """
    default_validators = []
    default_error_messages = {
        'required': _('This field is required.'),
        'invalid': _('Invalid value.'),
    }
    widget = widgets.TextInput
    default = None

    def __init__(self, source=None, read_only=False, required=None,
                 validators=[], error_messages=None, widget=None,
                 default=None, blank=None):

        super(WritableField, self).__init__(source=source)

        self.read_only = read_only
        if required is None:
            self.required = not(read_only)
        else:
            assert not read_only, "Cannot set required=True and read_only=True"
            self.required = required

        messages = {}
        for c in reversed(self.__class__.__mro__):
            messages.update(getattr(c, 'default_error_messages', {}))
        messages.update(error_messages or {})
        self.error_messages = messages

        self.validators = self.default_validators + validators
        self.default = default if default is not None else self.default
        self.blank = blank

        # Widgets are ony used for HTML forms.
        widget = widget or self.widget
        if isinstance(widget, type):
            widget = widget()
        self.widget = widget

    def validate(self, value):
        if value in validators.EMPTY_VALUES and self.required:
            raise ValidationError(self.error_messages['required'])

    def run_validators(self, value):
        if value in validators.EMPTY_VALUES:
            return
        errors = []
        for v in self.validators:
            try:
                v(value)
            except ValidationError as e:
                if hasattr(e, 'code') and e.code in self.error_messages:
                    message = self.error_messages[e.code]
                    if e.params:
                        message = message % e.params
                    errors.append(message)
                else:
                    errors.extend(e.messages)
        if errors:
            raise ValidationError(errors)

    def field_from_native(self, data, files, field_name, into):
        """
        Given a dictionary and a field name, updates the dictionary `into`,
        with the field and it's deserialized value.
        """
        if self.read_only:
            return

        try:
            if self._use_files:
                native = files[field_name]
            else:
                native = data[field_name]
        except KeyError:
            if self.default is not None:
                native = self.default
            else:
                if self.required:
                    raise ValidationError(self.error_messages['required'])
                return

        value = self.from_native(native)
        if self.source == '*':
            if value:
                into.update(value)
        else:
            self.validate(value)
            self.run_validators(value)
            into[self.source or field_name] = value

    def from_native(self, value):
        """
        Reverts a simple representation back to the field's value.
        """
        return value


class ModelField(WritableField):
    """
    A generic field that can be used against an arbitrary model field.
    """
    def __init__(self, *args, **kwargs):
        try:
            self.model_field = kwargs.pop('model_field')
        except:
            raise ValueError("ModelField requires 'model_field' kwarg")

        self.min_length = kwargs.pop('min_length',
                            getattr(self.model_field, 'min_length', None))
        self.max_length = kwargs.pop('max_length',
                            getattr(self.model_field, 'max_length', None))
        
        super(ModelField, self).__init__(*args, **kwargs)

        if self.min_length is not None:
            self.validators.append(validators.MinLengthValidator(self.min_length))
        if self.max_length is not None:
            self.validators.append(validators.MaxLengthValidator(self.max_length))

    def from_native(self, value):
        rel = getattr(self.model_field, "rel", None)
        if rel is not None:
            return rel.to._meta.get_field(rel.field_name).to_python(value)
        else:
            return self.model_field.to_python(value)

    def field_to_native(self, obj, field_name):
        value = self.model_field._get_val_from_obj(obj)
        if is_protected_type(value):
            return value
        return self.model_field.value_to_string(obj)

    def attributes(self):
        return {
            "type": self.model_field.get_internal_type()
        }

##### 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)
        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_text(obj)
        ident = smart_text(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

        value = data.get(field_name)
        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

    # 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_text(obj)
        ident = smart_text(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_text(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

    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_text(obj)
        ident = smart_text(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_text(data)
            raise ValidationError(msg)

### Slug relationships


class SlugRelatedField(RelatedField):
    default_read_only = False

    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):
    pass


### 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

    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.
    """
    pass


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)


##### Typed Fields #####

class BooleanField(WritableField):
    type_name = 'BooleanField'
    widget = widgets.CheckboxInput
    default_error_messages = {
        'invalid': _("'%s' value must be either True or False."),
    }
    empty = False

    # Note: we set default to `False` in order to fill in missing value not
    # supplied by html form.  TODO: Fix so that only html form input gets
    # this behavior.
    default = False

    def from_native(self, value):
        if value in ('t', 'True', '1'):
            return True
        if value in ('f', 'False', '0'):
            return False
        return bool(value)


class CharField(WritableField):
    type_name = 'CharField'

    def __init__(self, max_length=None, min_length=None, *args, **kwargs):
        self.max_length, self.min_length = max_length, min_length
        super(CharField, self).__init__(*args, **kwargs)
        if min_length is not None:
            self.validators.append(validators.MinLengthValidator(min_length))
        if max_length is not None:
            self.validators.append(validators.MaxLengthValidator(max_length))

    def validate(self, value):
        """
        Validates that the value is supplied (if required).
        """
        # if empty string and allow blank
        if self.blank and not value:
            return
        else:
            super(CharField, self).validate(value)

    def from_native(self, value):
        if isinstance(value, six.string_types) or value is None:
            return value
        return smart_text(value)


class URLField(CharField):
    type_name = 'URLField'

    def __init__(self, **kwargs):
        kwargs['max_length'] = kwargs.get('max_length', 200)
        kwargs['validators'] = [validators.URLValidator()]
        super(URLField, self).__init__(**kwargs)


class SlugField(CharField):
    type_name = 'SlugField'

    def __init__(self, *args, **kwargs):
        kwargs['max_length'] = kwargs.get('max_length', 50)
        super(SlugField, self).__init__(*args, **kwargs)


class ChoiceField(WritableField):
    type_name = 'ChoiceField'
    widget = widgets.Select
    default_error_messages = {
        'invalid_choice': _('Select a valid choice. %(value)s is not one of the available choices.'),
    }

    def __init__(self, choices=(), *args, **kwargs):
        super(ChoiceField, self).__init__(*args, **kwargs)
        self.choices = choices

    def _get_choices(self):
        return self._choices

    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)

    def validate(self, value):
        """
        Validates that the input is in self.choices.
        """
        super(ChoiceField, self).validate(value)
        if value and not self.valid_value(value):
            raise ValidationError(self.error_messages['invalid_choice'] % {'value': value})

    def valid_value(self, value):
        """
        Check to see if the provided value is a valid choice.
        """
        for k, v in self.choices:
            if isinstance(v, (list, tuple)):
                # This is an optgroup, so look inside the group for options
                for k2, v2 in v:
                    if value == smart_text(k2):
                        return True
            else:
                if value == smart_text(k):
                    return True
        return False


class EmailField(CharField):
    type_name = 'EmailField'

    default_error_messages = {
        'invalid': _('Enter a valid e-mail address.'),
    }
    default_validators = [validators.validate_email]

    def from_native(self, value):
        ret = super(EmailField, self).from_native(value)
        if ret is None:
            return None
        return ret.strip()

    def __deepcopy__(self, memo):
        result = copy.copy(self)
        memo[id(self)] = result
        #result.widget = copy.deepcopy(self.widget, memo)
        result.validators = self.validators[:]
        return result


class RegexField(CharField):
    type_name = 'RegexField'

    def __init__(self, regex, max_length=None, min_length=None, *args, **kwargs):
        super(RegexField, self).__init__(max_length, min_length, *args, **kwargs)
        self.regex = regex

    def _get_regex(self):
        return self._regex

    def _set_regex(self, regex):
        if isinstance(regex, six.string_types):
            regex = re.compile(regex)
        self._regex = regex
        if hasattr(self, '_regex_validator') and self._regex_validator in self.validators:
            self.validators.remove(self._regex_validator)
        self._regex_validator = validators.RegexValidator(regex=regex)
        self.validators.append(self._regex_validator)

    regex = property(_get_regex, _set_regex)

    def __deepcopy__(self, memo):
        result = copy.copy(self)
        memo[id(self)] = result
        result.validators = self.validators[:]
        return result


class DateField(WritableField):
    type_name = 'DateField'

    default_error_messages = {
        'invalid': _("'%s' value has an invalid date format. It must be "
                     "in YYYY-MM-DD format."),
        'invalid_date': _("'%s' value has the correct format (YYYY-MM-DD) "
                          "but it is an invalid date."),
    }
    empty = None

    def from_native(self, value):
        if value in validators.EMPTY_VALUES:
            return None

        if isinstance(value, datetime.datetime):
            if timezone and settings.USE_TZ and timezone.is_aware(value):
                # Convert aware datetimes to the default time zone
                # before casting them to dates (#17742).
                default_timezone = timezone.get_default_timezone()
                value = timezone.make_naive(value, default_timezone)
            return value.date()
        if isinstance(value, datetime.date):
            return value

        try:
            parsed = parse_date(value)
            if parsed is not None:
                return parsed
        except ValueError:
            msg = self.error_messages['invalid_date'] % value
            raise ValidationError(msg)

        msg = self.error_messages['invalid'] % value
        raise ValidationError(msg)


class DateTimeField(WritableField):
    type_name = 'DateTimeField'

    default_error_messages = {
        'invalid': _("'%s' value has an invalid format. It must be in "
                     "YYYY-MM-DD HH:MM[:ss[.uuuuuu]][TZ] format."),
        'invalid_date': _("'%s' value has the correct format "
                          "(YYYY-MM-DD) but it is an invalid date."),
        'invalid_datetime': _("'%s' value has the correct format "
                              "(YYYY-MM-DD HH:MM[:ss[.uuuuuu]][TZ]) "
                              "but it is an invalid date/time."),
    }
    empty = None

    def from_native(self, value):
        if value in validators.EMPTY_VALUES:
            return None

        if isinstance(value, datetime.datetime):
            return value
        if isinstance(value, datetime.date):
            value = datetime.datetime(value.year, value.month, value.day)
            if settings.USE_TZ:
                # For backwards compatibility, interpret naive datetimes in
                # local time. This won't work during DST change, but we can't
                # do much about it, so we let the exceptions percolate up the
                # call stack.
                warnings.warn("DateTimeField received a naive datetime (%s)"
                              " while time zone support is active." % value,
                              RuntimeWarning)
                default_timezone = timezone.get_default_timezone()
                value = timezone.make_aware(value, default_timezone)
            return value

        try:
            parsed = parse_datetime(value)
            if parsed is not None:
                return parsed
        except ValueError:
            msg = self.error_messages['invalid_datetime'] % value
            raise ValidationError(msg)

        try:
            parsed = parse_date(value)
            if parsed is not None:
                return datetime.datetime(parsed.year, parsed.month, parsed.day)
        except ValueError:
            msg = self.error_messages['invalid_date'] % value
            raise ValidationError(msg)

        msg = self.error_messages['invalid'] % value
        raise ValidationError(msg)


class IntegerField(WritableField):
    type_name = 'IntegerField'

    default_error_messages = {
        'invalid': _('Enter a whole number.'),
        'max_value': _('Ensure this value is less than or equal to %(limit_value)s.'),
        'min_value': _('Ensure this value is greater than or equal to %(limit_value)s.'),
    }

    def __init__(self, max_value=None, min_value=None, *args, **kwargs):
        self.max_value, self.min_value = max_value, min_value
        super(IntegerField, self).__init__(*args, **kwargs)

        if max_value is not None:
            self.validators.append(validators.MaxValueValidator(max_value))
        if min_value is not None:
            self.validators.append(validators.MinValueValidator(min_value))

    def from_native(self, value):
        if value in validators.EMPTY_VALUES:
            return None

        try:
            value = int(str(value))
        except (ValueError, TypeError):
            raise ValidationError(self.error_messages['invalid'])
        return value


class FloatField(WritableField):
    type_name = 'FloatField'

    default_error_messages = {
        'invalid': _("'%s' value must be a float."),
    }

    def from_native(self, value):
        if value in validators.EMPTY_VALUES:
            return None

        try:
            return float(value)
        except (TypeError, ValueError):
            msg = self.error_messages['invalid'] % value
            raise ValidationError(msg)


class FileField(WritableField):
    _use_files = True
    type_name = 'FileField'
    widget = widgets.FileInput

    default_error_messages = {
        'invalid': _("No file was submitted. Check the encoding type on the form."),
        'missing': _("No file was submitted."),
        'empty': _("The submitted file is empty."),
        'max_length': _('Ensure this filename has at most %(max)d characters (it has %(length)d).'),
        'contradiction': _('Please either submit a file or check the clear checkbox, not both.')
    }

    def __init__(self, *args, **kwargs):
        self.max_length = kwargs.pop('max_length', None)
        self.allow_empty_file = kwargs.pop('allow_empty_file', False)
        super(FileField, self).__init__(*args, **kwargs)

    def from_native(self, data):
        if data in validators.EMPTY_VALUES:
            return None

        # UploadedFile objects should have name and size attributes.
        try:
            file_name = data.name
            file_size = data.size
        except AttributeError:
            raise ValidationError(self.error_messages['invalid'])

        if self.max_length is not None and len(file_name) > self.max_length:
            error_values = {'max': self.max_length, 'length': len(file_name)}
            raise ValidationError(self.error_messages['max_length'] % error_values)
        if not file_name:
            raise ValidationError(self.error_messages['invalid'])
        if not self.allow_empty_file and not file_size:
            raise ValidationError(self.error_messages['empty'])

        return data

    def to_native(self, value):
        return value.name


class ImageField(FileField):
    _use_files = True

    default_error_messages = {
        'invalid_image': _("Upload a valid image. The file you uploaded was either not an image or a corrupted image."),
    }

    def from_native(self, data):
        """
        Checks that the file-upload field data contains a valid image (GIF, JPG,
        PNG, possibly others -- whatever the Python Imaging Library supports).
        """
        f = super(ImageField, self).from_native(data)
        if f is None:
            return None

        # Try to import PIL in either of the two ways it can end up installed.
        try:
            from PIL import Image
        except ImportError:
            import Image

        # We need to get a file object for PIL. We might have a path or we might
        # have to read the data into memory.
        if hasattr(data, 'temporary_file_path'):
            file = data.temporary_file_path()
        else:
            if hasattr(data, 'read'):
                file = BytesIO(data.read())
            else:
                file = BytesIO(data['content'])

        try:
            # load() could spot a truncated JPEG, but it loads the entire
            # image in memory, which is a DoS vector. See #3848 and #18520.
            # verify() must be called immediately after the constructor.
            Image.open(file).verify()
        except ImportError:
            # Under PyPy, it is possible to import PIL. However, the underlying
            # _imaging C module isn't available, so an ImportError will be
            # raised. Catch and re-raise.
            raise
        except Exception:  # Python Imaging Library doesn't recognize it as an image
            raise ValidationError(self.error_messages['invalid_image'])
        if hasattr(f, 'seek') and callable(f.seek):
            f.seek(0)
        return f


class SerializerMethodField(Field):
    """
    A field that gets its value by calling a method on the serializer it's attached to.
    """

    def __init__(self, method_name):
        self.method_name = method_name
        super(SerializerMethodField, self).__init__()

    def field_to_native(self, obj, field_name):
        value = getattr(self.parent, self.method_name)(obj)
        return self.to_native(value)