django之forms组件

在django中forms组件有其强大的功能，里面集合和众多的函数和方法：下面来看一下它的源码

"""
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 _

from .renderers import get_default_renderer

__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.
    default_renderer = None
    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, renderer=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

        # Initialize form renderer. Use a global default if not specified
        # either as an argument or as self.default_renderer.
        if renderer is None:
            if self.default_renderer is None:
                renderer = get_default_renderer()
            else:
                renderer = self.default_renderer
                if isinstance(self.default_renderer, type):
                    renderer = renderer()
        self.renderer = renderer

    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('
'.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.get_initial_for_field(field, name)
            else:
                value = field.widget.value_from_datadict(self.data, self.files, self.add_prefix(name))
            try:
                if isinstance(field, FileField):
                    initial = self.get_initial_for_field(field, name)
                    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:
                # Use the BoundField's initial as this is the value passed to
                # the widget.
                initial_value = self[name].initial
            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]

    def get_initial_for_field(self, field, field_name):
        """
        Return initial data for field on form. Use initial data from the form
        or the field, in that order. Evaluate callable values.
        """
        value = self.initial.get(field_name, field.initial)
        if callable(value):
            value = value()
        return value


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.

抛开其他的代码，我们之关注我们需要的东西

1 首先数据的验证通过的是is_vaild方法，它下面有以下东西

return self.is_bound and not self.errors  对照以下也就是is_bound不能为空，并且 errors方法返回的为空，则通过验证

2 我们找到 errors 方法，

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

3 找到 full_clean 方法

    def full_clean(self):
        """
        Cleans all of self.data and populates self._errors and
        self.cleaned_data.
        """
        self._errors = ErrorDict()   #先赋一个空的错误字典
        if not self.is_bound:  # Stop further processing.
            return
        self.cleaned_data = {}       #定义一个空的cleaned_data字典
        # 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
#执行下面三种方法
        self._clean_fields() 
        self._clean_form()
        self._post_clean()

4  找到 _clean_fields 方法

    def _clean_fields(self):
        for name, field in self.fields.items():  #依次遍历字段
            # 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.get_initial_for_field(field, name)
            else:
                value = field.widget.value_from_datadict(self.data, self.files, self.add_prefix(name))
            try:
                if isinstance(field, FileField):
                    initial = self.get_initial_for_field(field, name)
                    value = field.clean(value, initial)
                else:
                    value = field.clean(value)
                self.cleaned_data[name] = value   #通过自定义和django里面定义的方法后，将它加入到 cleand_data字典中
                if hasattr(self, 'clean_%s' % name):  #判断是否有自定义的局部钩子函数
                    value = getattr(self, 'clean_%s' % name)()  #通过了局部钩子则返回数据
                    self.cleaned_data[name] = value   #将数据加入 cleaned_data
            except ValidationError as e:
                self.add_error(name, e)  #错误的话执行 add_error

5 找到add_error

            self._errors[field].extend(error_list)  #将错误信息加入 _errors
            if field in self.cleaned_data:
                del self.cleaned_data[field]  #删除cleaned_data中这条数据，之前是通过自定义方法加入的，通不过 钩子函数

6 回到上面执行  self._clean_form()

    def _clean_form(self):
        try:
            cleaned_data = self.clean() #接着执行 clean（）全局钩子
        except ValidationError as e:
            self.add_error(None, e)
        else:
            if cleaned_data is not None:
                self.cleaned_data = cleaned_data

7接着查看 全局钩子  clean ，它只有一个返回的数据，因此我们可以自定义一个

    def clean(self):

        return self.cleaned_data  #注意返回的数据和局部钩子的区别

 8 最后查看 _post_clean ，说白了就是什么都没有

def _post_clean(self):
        pass

以上是源码内部执行的顺序，下面我们来看一个例子

 1 自定义判断字段

2 自定义局部钩子

3自定义全局钩子

4 继承并使用

5 .1在模板中显示一

 上面的代码 form_obj.errors.all_error  也可以改成  {{ form_obj.non_field_errors.0 }}

5.2 在模板中显示二

6在浏览器上面看效果

其他：

我们在forms组件中处理的不同情况