# Τεκμηρίωση του Django - 1.10.7

# Πηγαίος κώδικας για το django.forms.forms

    """
    Form classes
    """

    from __future__ import unicode_literals

    import copy
    from collections import OrderedDict

    from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
    # BoundField is imported for backwards compatibility in Django 1.9
    from django.forms.boundfield import BoundField  # NOQA
    from django.forms.fields import Field, FileField
    # pretty_name is imported for backwards compatibility in Django 1.9
    from django.forms.utils import ErrorDict, ErrorList, pretty_name  # NOQA
    from django.forms.widgets import Media, MediaDefiningClass
    from django.utils import six
    from django.utils.encoding import force_text, python_2_unicode_compatible
    from django.utils.functional import cached_property
    from django.utils.html import conditional_escape, html_safe
    from django.utils.safestring import mark_safe
    from django.utils.translation import ugettext as _

    __all__ = ('BaseForm', 'Form')

    class DeclarativeFieldsMetaclass(MediaDefiningClass):
        """
        Metaclass that collects Fields declared on the base classes.
        """
        def __new__(mcs, name, bases, attrs):
            # Collect fields from current class.
            current_fields = []
            for key, value in list(attrs.items()):
                if isinstance(value, Field):
                    current_fields.append((key, value))
                    attrs.pop(key)
            current_fields.sort(key=lambda x: x[1].creation_counter)
            attrs['declared_fields'] = OrderedDict(current_fields)

            new_class = super(DeclarativeFieldsMetaclass, mcs).__new__(mcs, name, bases, attrs)

            # Walk through the MRO.
            declared_fields = OrderedDict()
            for base in reversed(new_class.__mro__):
                # Collect fields from base class.
                if hasattr(base, 'declared_fields'):
                    declared_fields.update(base.declared_fields)

                # Field shadowing.
                for attr, value in base.__dict__.items():
                    if value is None and attr in declared_fields:
                        declared_fields.pop(attr)

            new_class.base_fields = declared_fields
            new_class.declared_fields = declared_fields

            return new_class

    @html_safe
    @python_2_unicode_compatible
    class BaseForm(object):
        # This is the main implementation of all the Form logic. Note that this
        # class is different than Form. See the comments by the Form class for more
        # information. Any improvements to the form API should be made to *this*
        # class, not to the Form class.
        field_order = None
        prefix = None
        use_required_attribute = True

        def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                     initial=None, error_class=ErrorList, label_suffix=None,
                     empty_permitted=False, field_order=None, use_required_attribute=None):
            self.is_bound = data is not None or files is not None
            self.data = data or {}
            self.files = files or {}
            self.auto_id = auto_id
            if prefix is not None:
                self.prefix = prefix
            self.initial = initial or {}
            self.error_class = error_class
            # Translators: This is the default suffix added to form field labels
            self.label_suffix = label_suffix if label_suffix is not None else _(':')
            self.empty_permitted = empty_permitted
            self._errors = None  # Stores the errors after clean() has been called.

            # The base_fields class attribute is the *class-wide* definition of
            # fields. Because a particular *instance* of the class might want to
            # alter self.fields, we create self.fields here by copying base_fields.
            # Instances should always modify self.fields; they should not modify
            # self.base_fields.
            self.fields = copy.deepcopy(self.base_fields)
            self._bound_fields_cache = {}
            self.order_fields(self.field_order if field_order is None else field_order)

            if use_required_attribute is not None:
                self.use_required_attribute = use_required_attribute

        def order_fields(self, field_order):
            """
            Rearranges the fields according to field_order.

            field_order is a list of field names specifying the order. Fields not
            included in the list are appended in the default order for backward
            compatibility with subclasses not overriding field_order. If field_order
            is None, all fields are kept in the order defined in the class.
            Unknown fields in field_order are ignored to allow disabling fields in
            form subclasses without redefining ordering.
            """
            if field_order is None:
                return
            fields = OrderedDict()
            for key in field_order:
                try:
                    fields[key] = self.fields.pop(key)
                except KeyError:  # ignore unknown fields
                    pass
            fields.update(self.fields)  # add remaining fields in original order
            self.fields = fields

        def __str__(self):
            return self.as_table()

        def __repr__(self):
            if self._errors is None:
                is_valid = "Unknown"
            else:
                is_valid = self.is_bound and not bool(self._errors)
            return '<%(cls)s bound=%(bound)s, valid=%(valid)s, fields=(%(fields)s)>' % {
                'cls': self.__class__.__name__,
                'bound': self.is_bound,
                'valid': is_valid,
                'fields': ';'.join(self.fields),
            }

        def __iter__(self):
            for name in self.fields:
                yield self[name]

        def __getitem__(self, name):
            "Returns a BoundField with the given name."
            try:
                field = self.fields[name]
            except KeyError:
                raise KeyError(
                    "Key '%s' not found in '%s'. Choices are: %s." % (
                        name,
                        self.__class__.__name__,
                        ', '.join(sorted(f for f in self.fields)),
                    )
                )
            if name not in self._bound_fields_cache:
                self._bound_fields_cache[name] = field.get_bound_field(self, name)
            return self._bound_fields_cache[name]

        @property
        def errors(self):
            "Returns an ErrorDict for the data provided for the form"
            if self._errors is None:
                self.full_clean()
            return self._errors

        def is_valid(self):
            """
            Returns True if the form has no errors. Otherwise, False. If errors are
            being ignored, returns False.
            """
            return self.is_bound and not self.errors

        def add_prefix(self, field_name):
            """
            Returns the field name with a prefix appended, if this Form has a
            prefix set.

            Subclasses may wish to override.
            """
            return '%s-%s' % (self.prefix, field_name) if self.prefix else field_name

        def add_initial_prefix(self, field_name):
            """
            Add a 'initial' prefix for checking dynamic initial values
            """
            return 'initial-%s' % self.add_prefix(field_name)

        def _html_output(self, normal_row, error_row, row_ender, help_text_html, errors_on_separate_row):
            "Helper function for outputting HTML. Used by as_table(), as_ul(), as_p()."
            top_errors = self.non_field_errors()  # Errors that should be displayed above all fields.
            output, hidden_fields = [], []

            for name, field in self.fields.items():
                html_class_attr = ''
                bf = self[name]
                # Escape and cache in local variable.
                bf_errors = self.error_class([conditional_escape(error) for error in bf.errors])
                if bf.is_hidden:
                    if bf_errors:
                        top_errors.extend(
                            [_('(Hidden field %(name)s) %(error)s') % {'name': name, 'error': force_text(e)}
                             for e in bf_errors])
                    hidden_fields.append(six.text_type(bf))
                else:
                    # Create a 'class="..."' attribute if the row should have any
                    # CSS classes applied.
                    css_classes = bf.css_classes()
                    if css_classes:
                        html_class_attr = ' class="%s"' % css_classes

                    if errors_on_separate_row and bf_errors:
                        output.append(error_row % force_text(bf_errors))

                    if bf.label:
                        label = conditional_escape(force_text(bf.label))
                        label = bf.label_tag(label) or ''
                    else:
                        label = ''

                    if field.help_text:
                        help_text = help_text_html % force_text(field.help_text)
                    else:
                        help_text = ''

                    output.append(normal_row % {
                        'errors': force_text(bf_errors),
                        'label': force_text(label),
                        'field': six.text_type(bf),
                        'help_text': help_text,
                        'html_class_attr': html_class_attr,
                        'css_classes': css_classes,
                        'field_name': bf.html_name,
                    })

            if top_errors:
                output.insert(0, error_row % force_text(top_errors))

            if hidden_fields:  # Insert any hidden fields in the last row.
                str_hidden = ''.join(hidden_fields)
                if output:
                    last_row = output[-1]
                    # Chop off the trailing row_ender (e.g. '</td></tr>') and
                    # insert the hidden fields.
                    if not last_row.endswith(row_ender):
                        # This can happen in the as_p() case (and possibly others
                        # that users write): if there are only top errors, we may
                        # not be able to conscript the last row for our purposes,
                        # so insert a new, empty row.
                        last_row = (normal_row % {
                            'errors': '',
                            'label': '',
                            'field': '',
                            'help_text': '',
                            'html_class_attr': html_class_attr,
                            'css_classes': '',
                            'field_name': '',
                        })
                        output.append(last_row)
                    output[-1] = last_row[:-len(row_ender)] + str_hidden + row_ender
                else:
                    # If there aren't any rows in the output, just append the
                    # hidden fields.
                    output.append(str_hidden)
            return mark_safe('\n'.join(output))

        def as_table(self):
            "Returns this form rendered as HTML <tr>s -- excluding the <table></table>."
            return self._html_output(
                normal_row='<tr%(html_class_attr)s><th>%(label)s</th><td>%(errors)s%(field)s%(help_text)s</td></tr>',
                error_row='<tr><td colspan="2">%s</td></tr>',
                row_ender='</td></tr>',
                help_text_html='<br /><span class="helptext">%s</span>',
                errors_on_separate_row=False)

        def as_ul(self):
            "Returns this form rendered as HTML <li>s -- excluding the <ul></ul>."
            return self._html_output(
                normal_row='<li%(html_class_attr)s>%(errors)s%(label)s %(field)s%(help_text)s</li>',
                error_row='<li>%s</li>',
                row_ender='</li>',
                help_text_html=' <span class="helptext">%s</span>',
                errors_on_separate_row=False)

        def as_p(self):
            "Returns this form rendered as HTML <p>s."
            return self._html_output(
                normal_row='<p%(html_class_attr)s>%(label)s %(field)s%(help_text)s</p>',
                error_row='%s',
                row_ender='</p>',
                help_text_html=' <span class="helptext">%s</span>',
                errors_on_separate_row=True)

        def non_field_errors(self):
            """
            Returns an ErrorList of errors that aren't associated with a particular
            field -- i.e., from Form.clean(). Returns an empty ErrorList if there
            are none.
            """
            return self.errors.get(NON_FIELD_ERRORS, self.error_class(error_class='nonfield'))

        def add_error(self, field, error):
            """
            Update the content of `self._errors`.

            The `field` argument is the name of the field to which the errors
            should be added. If its value is None the errors will be treated as
            NON_FIELD_ERRORS.

            The `error` argument can be a single error, a list of errors, or a
            dictionary that maps field names to lists of errors. What we define as
            an "error" can be either a simple string or an instance of
            ValidationError with its message attribute set and what we define as
            list or dictionary can be an actual `list` or `dict` or an instance
            of ValidationError with its `error_list` or `error_dict` attribute set.

            If `error` is a dictionary, the `field` argument *must* be None and
            errors will be added to the fields that correspond to the keys of the
            dictionary.
            """
            if not isinstance(error, ValidationError):
                # Normalize to ValidationError and let its constructor
                # do the hard work of making sense of the input.
                error = ValidationError(error)

            if hasattr(error, 'error_dict'):
                if field is not None:
                    raise TypeError(
                        "The argument `field` must be `None` when the `error` "
                        "argument contains errors for multiple fields."
                    )
                else:
                    error = error.error_dict
            else:
                error = {field or NON_FIELD_ERRORS: error.error_list}

            for field, error_list in error.items():
                if field not in self.errors:
                    if field != NON_FIELD_ERRORS and field not in self.fields:
                        raise ValueError(
                            "'%s' has no field named '%s'." % (self.__class__.__name__, field))
                    if field == NON_FIELD_ERRORS:
                        self._errors[field] = self.error_class(error_class='nonfield')
                    else:
                        self._errors[field] = self.error_class()
                self._errors[field].extend(error_list)
                if field in self.cleaned_data:
                    del self.cleaned_data[field]

        def has_error(self, field, code=None):
            if code is None:
                return field in self.errors
            if field in self.errors:
                for error in self.errors.as_data()[field]:
                    if error.code == code:
                        return True
            return False

        def full_clean(self):
            """
            Cleans all of self.data and populates self._errors and
            self.cleaned_data.
            """
            self._errors = ErrorDict()
            if not self.is_bound:  # Stop further processing.
                return
            self.cleaned_data = {}
            # If the form is permitted to be empty, and none of the form data has
            # changed from the initial data, short circuit any validation.
            if self.empty_permitted and not self.has_changed():
                return

            self._clean_fields()
            self._clean_form()
            self._post_clean()

        def _clean_fields(self):
            for name, field in self.fields.items():
                # value_from_datadict() gets the data from the data dictionaries.
                # Each widget type knows how to retrieve its own data, because some
                # widgets split data over several HTML fields.
                if field.disabled:
                    value = self.initial.get(name, field.initial)
                else:
                    value = field.widget.value_from_datadict(self.data, self.files, self.add_prefix(name))
                try:
                    if isinstance(field, FileField):
                        initial = self.initial.get(name, field.initial)
                        value = field.clean(value, initial)
                    else:
                        value = field.clean(value)
                    self.cleaned_data[name] = value
                    if hasattr(self, 'clean_%s' % name):
                        value = getattr(self, 'clean_%s' % name)()
                        self.cleaned_data[name] = value
                except ValidationError as e:
                    self.add_error(name, e)

        def _clean_form(self):
            try:
                cleaned_data = self.clean()
            except ValidationError as e:
                self.add_error(None, e)
            else:
                if cleaned_data is not None:
                    self.cleaned_data = cleaned_data

        def _post_clean(self):
            """
            An internal hook for performing additional cleaning after form cleaning
            is complete. Used for model validation in model forms.
            """
            pass

        def clean(self):
            """
            Hook for doing any extra form-wide cleaning after Field.clean() has been
            called on every field. Any ValidationError raised by this method will
            not be associated with a particular field; it will have a special-case
            association with the field named '__all__'.
            """
            return self.cleaned_data

        def has_changed(self):
            """
            Returns True if data differs from initial.
            """
            return bool(self.changed_data)

        @cached_property
        def changed_data(self):
            data = []
            for name, field in self.fields.items():
                prefixed_name = self.add_prefix(name)
                data_value = field.widget.value_from_datadict(self.data, self.files, prefixed_name)
                if not field.show_hidden_initial:
                    initial_value = self.initial.get(name, field.initial)
                    if callable(initial_value):
                        initial_value = initial_value()
                else:
                    initial_prefixed_name = self.add_initial_prefix(name)
                    hidden_widget = field.hidden_widget()
                    try:
                        initial_value = field.to_python(hidden_widget.value_from_datadict(
                            self.data, self.files, initial_prefixed_name))
                    except ValidationError:
                        # Always assume data has changed if validation fails.
                        data.append(name)
                        continue
                if field.has_changed(initial_value, data_value):
                    data.append(name)
            return data

        @property
        def media(self):
            """
            Provide a description of all media required to render the widgets on this form
            """
            media = Media()
            for field in self.fields.values():
                media = media + field.widget.media
            return media

        def is_multipart(self):
            """
            Returns True if the form needs to be multipart-encoded, i.e. it has
            FileInput. Otherwise, False.
            """
            for field in self.fields.values():
                if field.widget.needs_multipart_form:
                    return True
            return False

        def hidden_fields(self):
            """
            Returns a list of all the BoundField objects that are hidden fields.
            Useful for manual form layout in templates.
            """
            return [field for field in self if field.is_hidden]

        def visible_fields(self):
            """
            Returns a list of BoundField objects that aren't hidden fields.
            The opposite of the hidden_fields() method.
            """
            return [field for field in self if not field.is_hidden]

    class Form(six.with_metaclass(DeclarativeFieldsMetaclass, BaseForm)):
        "A collection of Fields, plus their associated data."
        # This is a separate class from BaseForm in order to abstract the way
        # self.fields is specified. This class (Form) is the one that does the
        # fancy metaclass stuff purely for the semantic sugar -- it allows one
        # to define a form using declarative syntax.
        # BaseForm itself has no way of designating self.fields.