fields.py

"""
Field classes.
"""

from __future__ import absolute_import, unicode_literals

import copy
import datetime
import os
import re
import sys
from decimal import Decimal, DecimalException
from io import BytesIO

from django.core import validators
from django.core.exceptions import ValidationError
from django.forms.util import ErrorList, from_current_timezone, to_current_timezone
from django.forms.widgets import (
    TextInput, NumberInput, EmailInput, URLInput, HiddenInput,
    MultipleHiddenInput, ClearableFileInput, CheckboxInput, Select,
    NullBooleanSelect, SelectMultiple, DateInput, DateTimeInput, TimeInput,
    SplitDateTimeWidget, SplitHiddenDateTimeWidget, FILE_INPUT_CONTRADICTION
)
from django.utils import formats
from django.utils.encoding import smart_text, force_str, force_text
from django.utils.ipv6 import clean_ipv6_address
from django.utils import six
from django.utils.six.moves.urllib.parse import urlsplit, urlunsplit
from django.utils.translation import ugettext_lazy as _, ungettext_lazy

# Provide this import for backwards compatibility.
from django.core.validators import EMPTY_VALUES


__all__ = (
    'Field', 'CharField', 'IntegerField',
    'DateField', 'TimeField', 'DateTimeField', 'TimeField',
    'RegexField', 'EmailField', 'FileField', 'ImageField', 'URLField',
    'BooleanField', 'NullBooleanField', 'ChoiceField', 'MultipleChoiceField',
    'ComboField', 'MultiValueField', 'FloatField', 'DecimalField',
    'SplitDateTimeField', 'IPAddressField', 'GenericIPAddressField', 'FilePathField',
    'SlugField', 'TypedChoiceField', 'TypedMultipleChoiceField'
)


class Field(object):
    widget = TextInput # Default widget to use when rendering this type of Field.
    hidden_widget = HiddenInput # Default widget to use when rendering this as "hidden".
    default_validators = [] # Default set of validators
    # Add an 'invalid' entry to default_error_message if you want a specific
    # field error message not raised by the field validators.
    default_error_messages = {
        'required': _('This field is required.'),
    }
    empty_values = list(validators.EMPTY_VALUES)

    # Tracks each time a Field instance is created. Used to retain order.
    creation_counter = 0

    def __init__(self, required=True, widget=None, label=None, initial=None,
                 help_text='', error_messages=None, show_hidden_initial=False,
                 validators=[], localize=False):
        # required -- Boolean that specifies whether the field is required.
        #             True by default.
        # widget -- A Widget class, or instance of a Widget class, that should
        #           be used for this Field when displaying it. Each Field has a
        #           default Widget that it'll use if you don't specify this. In
        #           most cases, the default widget is TextInput.
        # label -- A verbose name for this field, for use in displaying this
        #          field in a form. By default, Django will use a "pretty"
        #          version of the form field name, if the Field is part of a
        #          Form.
        # initial -- A value to use in this Field's initial display. This value
        #            is *not* used as a fallback if data isn't given.
        # help_text -- An optional string to use as "help text" for this Field.
        # error_messages -- An optional dictionary to override the default
        #                   messages that the field will raise.
        # show_hidden_initial -- Boolean that specifies if it is needed to render a
        #                        hidden widget with initial value after widget.
        # validators -- List of addtional validators to use
        # localize -- Boolean that specifies if the field should be localized.
        self.required, self.label, self.initial = required, label, initial
        self.show_hidden_initial = show_hidden_initial
        self.help_text = help_text
        widget = widget or self.widget
        if isinstance(widget, type):
            widget = widget()

        # Trigger the localization machinery if needed.
        self.localize = localize
        if self.localize:
            widget.is_localized = True

        # Let the widget know whether it should display as required.
        widget.is_required = self.required

        # Hook into self.widget_attrs() for any Field-specific HTML attributes.
        extra_attrs = self.widget_attrs(widget)
        if extra_attrs:
            widget.attrs.update(extra_attrs)

        self.widget = widget

        # Increase the creation counter, and save our local copy.
        self.creation_counter = Field.creation_counter
        Field.creation_counter += 1

        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
        super(Field, self).__init__()

    def prepare_value(self, value):
        return value

    def to_python(self, value):
        return value

    def validate(self, value):
        if value in self.empty_values and self.required:
            raise ValidationError(self.error_messages['required'], code='required')

    def run_validators(self, value):
        if value in self.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:
                    e.message = self.error_messages[e.code]
                errors.extend(e.error_list)
        if errors:
            raise ValidationError(errors)

    def clean(self, value):
        """
        Validates the given value and returns its "cleaned" value as an
        appropriate Python object.

        Raises ValidationError for any errors.
        """
        value = self.to_python(value)
        self.validate(value)
        self.run_validators(value)
        return value

    def bound_data(self, data, initial):
        """
        Return the value that should be shown for this field on render of a
        bound form, given the submitted POST data for the field and the initial
        data, if any.

        For most fields, this will simply be data; FileFields need to handle it
        a bit differently.
        """
        return data

    def widget_attrs(self, widget):
        """
        Given a Widget instance (*not* a Widget class), returns a dictionary of
        any HTML attributes that should be added to the Widget, based on this
        Field.
        """
        return {}

    def _has_changed(self, initial, data):
        """
        Return True if data differs from initial.
        """
        # For purposes of seeing whether something has changed, None is
        # the same as an empty string, if the data or inital value we get
        # is None, replace it w/ ''.
        initial_value = initial if initial is not None else ''
        try:
            data = self.to_python(data)
        except ValidationError:
            return True
        data_value = data if data is not None else ''
        return initial_value != data_value

    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 CharField(Field):
    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(int(min_length)))
        if max_length is not None:
            self.validators.append(validators.MaxLengthValidator(int(max_length)))

    def to_python(self, value):
        "Returns a Unicode object."
        if value in self.empty_values:
            return ''
        return smart_text(value)

    def widget_attrs(self, widget):
        attrs = super(CharField, self).widget_attrs(widget)
        if self.max_length is not None and isinstance(widget, TextInput):
            # The HTML attribute is maxlength, not max_length.
            attrs.update({'maxlength': str(self.max_length)})
        return attrs


class IntegerField(Field):
    widget = NumberInput
    default_error_messages = {
        'invalid': _('Enter a whole number.'),
    }

    def __init__(self, max_value=None, min_value=None, *args, **kwargs):
        self.max_value, self.min_value = max_value, min_value
        if kwargs.get('localize') and self.widget == NumberInput:
            # Localized number input is not well supported on most browsers
            kwargs.setdefault('widget', super(IntegerField, self).widget)
        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 to_python(self, value):
        """
        Validates that int() can be called on the input. Returns the result
        of int(). Returns None for empty values.
        """
        value = super(IntegerField, self).to_python(value)
        if value in self.empty_values:
            return None
        if self.localize:
            value = formats.sanitize_separators(value)
        try:
            value = int(str(value))
        except (ValueError, TypeError):
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        return value

    def widget_attrs(self, widget):
        attrs = super(IntegerField, self).widget_attrs(widget)
        if isinstance(widget, NumberInput):
            if self.min_value is not None:
                attrs['min'] = self.min_value
            if self.max_value is not None:
                attrs['max'] = self.max_value
        return attrs


class FloatField(IntegerField):
    default_error_messages = {
        'invalid': _('Enter a number.'),
    }

    def to_python(self, value):
        """
        Validates that float() can be called on the input. Returns the result
        of float(). Returns None for empty values.
        """
        value = super(IntegerField, self).to_python(value)
        if value in self.empty_values:
            return None
        if self.localize:
            value = formats.sanitize_separators(value)
        try:
            value = float(value)
        except (ValueError, TypeError):
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        return value

    def widget_attrs(self, widget):
        attrs = super(FloatField, self).widget_attrs(widget)
        if isinstance(widget, NumberInput):
            attrs.setdefault('step', 'any')
        return attrs


class DecimalField(IntegerField):
    default_error_messages = {
        'invalid': _('Enter a number.'),
        'max_digits': ungettext_lazy(
            'Ensure that there are no more than %(max)s digit in total.',
            'Ensure that there are no more than %(max)s digits in total.',
            'max'),
        'max_decimal_places': ungettext_lazy(
            'Ensure that there are no more than %(max)s decimal place.',
            'Ensure that there are no more than %(max)s decimal places.',
            'max'),
        'max_whole_digits': ungettext_lazy(
            'Ensure that there are no more than %(max)s digit before the decimal point.',
            'Ensure that there are no more than %(max)s digits before the decimal point.',
            'max'),
    }

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

    def to_python(self, value):
        """
        Validates that the input is a decimal number. Returns a Decimal
        instance. Returns None for empty values. Ensures that there are no more
        than max_digits in the number, and no more than decimal_places digits
        after the decimal point.
        """
        if value in self.empty_values:
            return None
        if self.localize:
            value = formats.sanitize_separators(value)
        value = smart_text(value).strip()
        try:
            value = Decimal(value)
        except DecimalException:
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        return value

    def validate(self, value):
        super(DecimalField, self).validate(value)
        if value in self.empty_values:
            return
        # Check for NaN, Inf and -Inf values. We can't compare directly for NaN,
        # since it is never equal to itself. However, NaN is the only value that
        # isn't equal to itself, so we can use this to identify NaN
        if value != value or value == Decimal("Inf") or value == Decimal("-Inf"):
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        sign, digittuple, exponent = value.as_tuple()
        decimals = abs(exponent)
        # digittuple doesn't include any leading zeros.
        digits = len(digittuple)
        if decimals > digits:
            # We have leading zeros up to or past the decimal point.  Count
            # everything past the decimal point as a digit.  We do not count
            # 0 before the decimal point as a digit since that would mean
            # we would not allow max_digits = decimal_places.
            digits = decimals
        whole_digits = digits - decimals

        if self.max_digits is not None and digits > self.max_digits:
            raise ValidationError(
                self.error_messages['max_digits'],
                code='max_digits',
                params={'max': self.max_digits},
            )
        if self.decimal_places is not None and decimals > self.decimal_places:
            raise ValidationError(
                self.error_messages['max_decimal_places'],
                code='max_decimal_places',
                params={'max': self.decimal_places},
            )
        if (self.max_digits is not None and self.decimal_places is not None
                and whole_digits > (self.max_digits - self.decimal_places)):
            raise ValidationError(
                self.error_messages['max_whole_digits'],
                code='max_whole_digits',
                params={'max': (self.max_digits - self.decimal_places)},
            )
        return value

    def widget_attrs(self, widget):
        attrs = super(DecimalField, self).widget_attrs(widget)
        if isinstance(widget, NumberInput):
            if self.decimal_places is not None:
                # Use exponential notation for small values since they might
                # be parsed as 0 otherwise. ref #20765
                step = str(Decimal('1') / 10 ** self.decimal_places).lower()
            else:
                step = 'any'
            attrs.setdefault('step', step)
        return attrs


class BaseTemporalField(Field):

    def __init__(self, input_formats=None, *args, **kwargs):
        super(BaseTemporalField, self).__init__(*args, **kwargs)
        if input_formats is not None:
            self.input_formats = input_formats

    def to_python(self, value):
        # Try to coerce the value to unicode.
        unicode_value = force_text(value, strings_only=True)
        if isinstance(unicode_value, six.text_type):
            value = unicode_value.strip()
        # If unicode, try to strptime against each input format.
        if isinstance(value, six.text_type):
            for format in self.input_formats:
                try:
                    return self.strptime(value, format)
                except (ValueError, TypeError):
                    continue
        raise ValidationError(self.error_messages['invalid'], code='invalid')

    def strptime(self, value, format):
        raise NotImplementedError('Subclasses must define this method.')


class DateField(BaseTemporalField):
    widget = DateInput
    input_formats = formats.get_format_lazy('DATE_INPUT_FORMATS')
    default_error_messages = {
        'invalid': _('Enter a valid date.'),
    }

    def to_python(self, value):
        """
        Validates that the input can be converted to a date. Returns a Python
        datetime.date object.
        """
        if value in self.empty_values:
            return None
        if isinstance(value, datetime.datetime):
            return value.date()
        if isinstance(value, datetime.date):
            return value
        return super(DateField, self).to_python(value)

    def strptime(self, value, format):
        return datetime.datetime.strptime(force_str(value), format).date()


class TimeField(BaseTemporalField):
    widget = TimeInput
    input_formats = formats.get_format_lazy('TIME_INPUT_FORMATS')
    default_error_messages = {
        'invalid': _('Enter a valid time.')
    }

    def to_python(self, value):
        """
        Validates that the input can be converted to a time. Returns a Python
        datetime.time object.
        """
        if value in self.empty_values:
            return None
        if isinstance(value, datetime.time):
            return value
        return super(TimeField, self).to_python(value)

    def strptime(self, value, format):
        return datetime.datetime.strptime(force_str(value), format).time()


class DateTimeField(BaseTemporalField):
    widget = DateTimeInput
    input_formats = formats.get_format_lazy('DATETIME_INPUT_FORMATS')
    default_error_messages = {
        'invalid': _('Enter a valid date/time.'),
    }

    def prepare_value(self, value):
        if isinstance(value, datetime.datetime):
            value = to_current_timezone(value)
        return value

    def to_python(self, value):
        """
        Validates that the input can be converted to a datetime. Returns a
        Python datetime.datetime object.
        """
        if value in self.empty_values:
            return None
        if isinstance(value, datetime.datetime):
            return from_current_timezone(value)
        if isinstance(value, datetime.date):
            result = datetime.datetime(value.year, value.month, value.day)
            return from_current_timezone(result)
        if isinstance(value, list):
            # Input comes from a SplitDateTimeWidget, for example. So, it's two
            # components: date and time.
            if len(value) != 2:
                raise ValidationError(self.error_messages['invalid'], code='invalid')
            if value[0] in self.empty_values and value[1] in self.empty_values:
                return None
            value = '%s %s' % tuple(value)
        result = super(DateTimeField, self).to_python(value)
        return from_current_timezone(result)

    def strptime(self, value, format):
        return datetime.datetime.strptime(force_str(value), format)


class RegexField(CharField):
    def __init__(self, regex, max_length=None, min_length=None, error_message=None, *args, **kwargs):
        """
        regex can be either a string or a compiled regular expression object.
        error_message is an optional error message to use, if
        'Enter a valid value' is too generic for you.
        """
        # error_message is just kept for backwards compatibility:
        if error_message:
            error_messages = kwargs.get('error_messages') or {}
            error_messages['invalid'] = error_message
            kwargs['error_messages'] = error_messages
        super(RegexField, self).__init__(max_length, min_length, *args, **kwargs)
        self._set_regex(regex)

    def _get_regex(self):
        return self._regex

    def _set_regex(self, regex):
        if isinstance(regex, six.string_types):
            regex = re.compile(regex, re.UNICODE)
        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)


class EmailField(CharField):
    widget = EmailInput
    default_validators = [validators.validate_email]

    def clean(self, value):
        value = self.to_python(value).strip()
        return super(EmailField, self).clean(value)


class FileField(Field):
    widget = ClearableFileInput
    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': ungettext_lazy(
            'Ensure this filename has at most %(max)d character (it has %(length)d).',
            'Ensure this filename has at most %(max)d characters (it has %(length)d).',
            'max'),
        '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 to_python(self, data):
        if data in self.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'], code='invalid')

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

        return data

    def clean(self, data, initial=None):
        # If the widget got contradictory inputs, we raise a validation error
        if data is FILE_INPUT_CONTRADICTION:
            raise ValidationError(self.error_messages['contradiction'], code='contradiction')
        # False means the field value should be cleared; further validation is
        # not needed.
        if data is False:
            if not self.required:
                return False
            # If the field is required, clearing is not possible (the widget
            # shouldn't return False data in that case anyway). False is not
            # in self.empty_value; if a False value makes it this far
            # it should be validated from here on out as None (so it will be
            # caught by the required check).
            data = None
        if not data and initial:
            return initial
        return super(FileField, self).clean(data)

    def bound_data(self, data, initial):
        if data in (None, FILE_INPUT_CONTRADICTION):
            return initial
        return data

    def _has_changed(self, initial, data):
        if data is None:
            return False
        return True


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

    def to_python(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).to_python(data)
        if f is None:
            return None

        from django.utils.image import Image

        # We need to get a file object for Pillow. 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 Exception:
            # Pillow (or PIL) doesn't recognize it as an image.
            six.reraise(ValidationError, ValidationError(
                self.error_messages['invalid_image'],
                code='invalid_image',
            ), sys.exc_info()[2])
        if hasattr(f, 'seek') and callable(f.seek):
            f.seek(0)
        return f


class URLField(CharField):
    widget = URLInput
    default_error_messages = {
        'invalid': _('Enter a valid URL.'),
    }
    default_validators = [validators.URLValidator()]

    def to_python(self, value):

        def split_url(url):
            """
            Returns a list of url parts via ``urlparse.urlsplit`` (or raises a
            ``ValidationError`` exception for certain).
            """
            try:
                return list(urlsplit(url))
            except ValueError:
                # urlparse.urlsplit can raise a ValueError with some
                # misformatted URLs.
                raise ValidationError(self.error_messages['invalid'], code='invalid')

        value = super(URLField, self).to_python(value)
        if value:
            url_fields = split_url(value)
            if not url_fields[0]:
                # If no URL scheme given, assume http://
                url_fields[0] = 'http'
            if not url_fields[1]:
                # Assume that if no domain is provided, that the path segment
                # contains the domain.
                url_fields[1] = url_fields[2]
                url_fields[2] = ''
                # Rebuild the url_fields list, since the domain segment may now
                # contain the path too.
                url_fields = split_url(urlunsplit(url_fields))
            if not url_fields[2]:
                # the path portion may need to be added before query params
                url_fields[2] = '/'
            value = urlunsplit(url_fields)
        return value

    def clean(self, value):
        value = self.to_python(value).strip()
        return super(URLField, self).clean(value)


class BooleanField(Field):
    widget = CheckboxInput

    def to_python(self, value):
        """Returns a Python boolean object."""
        # Explicitly check for the string 'False', which is what a hidden field
        # will submit for False. Also check for '0', since this is what
        # RadioSelect will provide. Because bool("True") == bool('1') == True,
        # we don't need to handle that explicitly.
        if isinstance(value, six.string_types) and value.lower() in ('false', '0'):
            value = False
        else:
            value = bool(value)
        return super(BooleanField, self).to_python(value)

    def validate(self, value):
        if not value and self.required:
            raise ValidationError(self.error_messages['required'], code='required')

    def _has_changed(self, initial, data):
        # Sometimes data or initial could be None or '' which should be the
        # same thing as False.
        if initial == 'False':
            # show_hidden_initial may have transformed False to 'False'
            initial = False
        return bool(initial) != bool(data)


class NullBooleanField(BooleanField):
    """
    A field whose valid values are None, True and False. Invalid values are
    cleaned to None.
    """
    widget = NullBooleanSelect

    def to_python(self, value):
        """
        Explicitly checks for the string 'True' and 'False', which is what a
        hidden field will submit for True and False, and for '1' and '0', which
        is what a RadioField will submit. Unlike the Booleanfield we need to
        explicitly check for True, because we are not using the bool() function
        """
        if value in (True, 'True', '1'):
            return True
        elif value in (False, 'False', '0'):
            return False
        else:
            return None

    def validate(self, value):
        pass

    def _has_changed(self, initial, data):
        # None (unknown) and False (No) are not the same
        if initial is not None:
            initial = bool(initial)
        if data is not None:
            data = bool(data)
        return initial != data


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

    def __init__(self, choices=(), required=True, widget=None, label=None,
                 initial=None, help_text='', *args, **kwargs):
        super(ChoiceField, self).__init__(required=required, widget=widget, label=label,
                                        initial=initial, help_text=help_text, *args, **kwargs)
        self.choices = choices

    def __deepcopy__(self, memo):
        result = super(ChoiceField, self).__deepcopy__(memo)
        result._choices = copy.deepcopy(self._choices, memo)
        return result

    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 to_python(self, value):
        "Returns a Unicode object."
        if value in self.empty_values:
            return ''
        return smart_text(value)

    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'],
                code='invalid_choice',
                params={'value': value},
            )

    def valid_value(self, value):
        "Check to see if the provided value is a valid choice"
        text_value = force_text(value)
        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 == k2 or text_value == force_text(k2):
                        return True
            else:
                if value == k or text_value == force_text(k):
                    return True
        return False


class TypedChoiceField(ChoiceField):
    def __init__(self, *args, **kwargs):
        self.coerce = kwargs.pop('coerce', lambda val: val)
        self.empty_value = kwargs.pop('empty_value', '')
        super(TypedChoiceField, self).__init__(*args, **kwargs)

    def to_python(self, value):
        """
        Validates that the value is in self.choices and can be coerced to the
        right type.
        """
        value = super(TypedChoiceField, self).to_python(value)
        if value == self.empty_value or value in self.empty_values:
            return self.empty_value
        try:
            value = self.coerce(value)
        except (ValueError, TypeError, ValidationError):
            raise ValidationError(
                self.error_messages['invalid_choice'],
                code='invalid_choice',
                params={'value': value},
            )
        return value


class MultipleChoiceField(ChoiceField):
    hidden_widget = MultipleHiddenInput
    widget = SelectMultiple
    default_error_messages = {
        'invalid_choice': _('Select a valid choice. %(value)s is not one of the available choices.'),
        'invalid_list': _('Enter a list of values.'),
    }

    def to_python(self, value):
        if not value:
            return []
        elif not isinstance(value, (list, tuple)):
            raise ValidationError(self.error_messages['invalid_list'], code='invalid_list')
        return [smart_text(val) for val in value]

    def validate(self, value):
        """
        Validates that the input is a list or tuple.
        """
        if self.required and not value:
            raise ValidationError(self.error_messages['required'], code='required')
        # Validate that each value in the value list is in self.choices.
        for val in value:
            if not self.valid_value(val):
                raise ValidationError(
                    self.error_messages['invalid_choice'],
                    code='invalid_choice',
                    params={'value': val},
                )

    def _has_changed(self, initial, data):
        if initial is None:
            initial = []
        if data is None:
            data = []
        if len(initial) != len(data):
            return True
        initial_set = set([force_text(value) for value in initial])
        data_set = set([force_text(value) for value in data])
        return data_set != initial_set


class TypedMultipleChoiceField(MultipleChoiceField):
    def __init__(self, *args, **kwargs):
        self.coerce = kwargs.pop('coerce', lambda val: val)
        self.empty_value = kwargs.pop('empty_value', [])
        super(TypedMultipleChoiceField, self).__init__(*args, **kwargs)

    def to_python(self, value):
        """
        Validates that the values are in self.choices and can be coerced to the
        right type.
        """
        value = super(TypedMultipleChoiceField, self).to_python(value)
        if value == self.empty_value or value in self.empty_values:
            return self.empty_value
        new_value = []
        for choice in value:
            try:
                new_value.append(self.coerce(choice))
            except (ValueError, TypeError, ValidationError):
                raise ValidationError(
                    self.error_messages['invalid_choice'],
                    code='invalid_choice',
                    params={'value': choice},
                )
        return new_value

    def validate(self, value):
        if value != self.empty_value:
            super(TypedMultipleChoiceField, self).validate(value)
        elif self.required:
            raise ValidationError(self.error_messages['required'], code='required')


class ComboField(Field):
    """
    A Field whose clean() method calls multiple Field clean() methods.
    """
    def __init__(self, fields=(), *args, **kwargs):
        super(ComboField, self).__init__(*args, **kwargs)
        # Set 'required' to False on the individual fields, because the
        # required validation will be handled by ComboField, not by those
        # individual fields.
        for f in fields:
            f.required = False
        self.fields = fields

    def clean(self, value):
        """
        Validates the given value against all of self.fields, which is a
        list of Field instances.
        """
        super(ComboField, self).clean(value)
        for field in self.fields:
            value = field.clean(value)
        return value


class MultiValueField(Field):
    """
    A Field that aggregates the logic of multiple Fields.

    Its clean() method takes a "decompressed" list of values, which are then
    cleaned into a single value according to self.fields. Each value in
    this list is cleaned by the corresponding field -- the first value is
    cleaned by the first field, the second value is cleaned by the second
    field, etc. Once all fields are cleaned, the list of clean values is
    "compressed" into a single value.

    Subclasses should not have to implement clean(). Instead, they must
    implement compress(), which takes a list of valid values and returns a
    "compressed" version of those values -- a single value.

    You'll probably want to use this with MultiWidget.
    """
    default_error_messages = {
        'invalid': _('Enter a list of values.'),
    }

    def __init__(self, fields=(), *args, **kwargs):
        super(MultiValueField, self).__init__(*args, **kwargs)
        # Set 'required' to False on the individual fields, because the
        # required validation will be handled by MultiValueField, not by those
        # individual fields.
        for f in fields:
            f.required = False
        self.fields = fields

    def validate(self, value):
        pass

    def clean(self, value):
        """
        Validates every value in the given list. A value is validated against
        the corresponding Field in self.fields.

        For example, if this MultiValueField was instantiated with
        fields=(DateField(), TimeField()), clean() would call
        DateField.clean(value[0]) and TimeField.clean(value[1]).
        """
        clean_data = []
        errors = ErrorList()
        if not value or isinstance(value, (list, tuple)):
            if not value or not [v for v in value if v not in self.empty_values]:
                if self.required:
                    raise ValidationError(self.error_messages['required'], code='required')
                else:
                    return self.compress([])
        else:
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        for i, field in enumerate(self.fields):
            try:
                field_value = value[i]
            except IndexError:
                field_value = None
            if self.required and field_value in self.empty_values:
                raise ValidationError(self.error_messages['required'], code='required')
            try:
                clean_data.append(field.clean(field_value))
            except ValidationError as e:
                # Collect all validation errors in a single list, which we'll
                # raise at the end of clean(), rather than raising a single
                # exception for the first error we encounter.
                errors.extend(e.error_list)
        if errors:
            raise ValidationError(errors)

        out = self.compress(clean_data)
        self.validate(out)
        self.run_validators(out)
        return out

    def compress(self, data_list):
        """
        Returns a single value for the given list of values. The values can be
        assumed to be valid.

        For example, if this MultiValueField was instantiated with
        fields=(DateField(), TimeField()), this might return a datetime
        object created by combining the date and time in data_list.
        """
        raise NotImplementedError('Subclasses must implement this method.')

    def _has_changed(self, initial, data):
        if initial is None:
            initial = ['' for x in range(0, len(data))]
        else:
            if not isinstance(initial, list):
                initial = self.widget.decompress(initial)
        for field, initial, data in zip(self.fields, initial, data):
            if field._has_changed(field.to_python(initial), data):
                return True
        return False


class FilePathField(ChoiceField):
    def __init__(self, path, match=None, recursive=False, allow_files=True,
                 allow_folders=False, required=True, widget=None, label=None,
                 initial=None, help_text='', *args, **kwargs):
        self.path, self.match, self.recursive = path, match, recursive
        self.allow_files, self.allow_folders = allow_files, allow_folders
        super(FilePathField, self).__init__(choices=(), required=required,
            widget=widget, label=label, initial=initial, help_text=help_text,
            *args, **kwargs)

        if self.required:
            self.choices = []
        else:
            self.choices = [("", "---------")]

        if self.match is not None:
            self.match_re = re.compile(self.match)

        if recursive:
            for root, dirs, files in sorted(os.walk(self.path)):
                if self.allow_files:
                    for f in files:
                        if self.match is None or self.match_re.search(f):
                            f = os.path.join(root, f)
                            self.choices.append((f, f.replace(path, "", 1)))
                if self.allow_folders:
                    for f in dirs:
                        if f == '__pycache__':
                            continue
                        if self.match is None or self.match_re.search(f):
                            f = os.path.join(root, f)
                            self.choices.append((f, f.replace(path, "", 1)))
        else:
            try:
                for f in sorted(os.listdir(self.path)):
                    if f == '__pycache__':
                        continue
                    full_file = os.path.join(self.path, f)
                    if (((self.allow_files and os.path.isfile(full_file)) or
                        (self.allow_folders and os.path.isdir(full_file))) and
                        (self.match is None or self.match_re.search(f))):
                        self.choices.append((full_file, f))
            except OSError:
                pass

        self.widget.choices = self.choices


class SplitDateTimeField(MultiValueField):
    widget = SplitDateTimeWidget
    hidden_widget = SplitHiddenDateTimeWidget
    default_error_messages = {
        'invalid_date': _('Enter a valid date.'),
        'invalid_time': _('Enter a valid time.'),
    }

    def __init__(self, input_date_formats=None, input_time_formats=None, *args, **kwargs):
        errors = self.default_error_messages.copy()
        if 'error_messages' in kwargs:
            errors.update(kwargs['error_messages'])
        localize = kwargs.get('localize', False)
        fields = (
            DateField(input_formats=input_date_formats,
                      error_messages={'invalid': errors['invalid_date']},
                      localize=localize),
            TimeField(input_formats=input_time_formats,
                      error_messages={'invalid': errors['invalid_time']},
                      localize=localize),
        )
        super(SplitDateTimeField, self).__init__(fields, *args, **kwargs)

    def compress(self, data_list):
        if data_list:
            # Raise a validation error if time or date is empty
            # (possible if SplitDateTimeField has required=False).
            if data_list[0] in self.empty_values:
                raise ValidationError(self.error_messages['invalid_date'], code='invalid_date')
            if data_list[1] in self.empty_values:
                raise ValidationError(self.error_messages['invalid_time'], code='invalid_time')
            result = datetime.datetime.combine(*data_list)
            return from_current_timezone(result)
        return None


class IPAddressField(CharField):
    default_validators = [validators.validate_ipv4_address]

    def to_python(self, value):
        if value in self.empty_values:
            return ''
        return value.strip()


class GenericIPAddressField(CharField):
    def __init__(self, protocol='both', unpack_ipv4=False, *args, **kwargs):
        self.unpack_ipv4 = unpack_ipv4
        self.default_validators = validators.ip_address_validators(protocol, unpack_ipv4)[0]
        super(GenericIPAddressField, self).__init__(*args, **kwargs)

    def to_python(self, value):
        if value in self.empty_values:
            return ''
        value = value.strip()
        if value and ':' in value:
            return clean_ipv6_address(value, self.unpack_ipv4)
        return value


class SlugField(CharField):
    default_validators = [validators.validate_slug]

    def clean(self, value):
        value = self.to_python(value).strip()
        return super(SlugField, self).clean(value)