本文例項講述了django框架forms元件用法。分享給大家供大家參考，具體如下：

在django中forms元件有其強大的功能，裡面集合和眾多的函式和方法：下面來看一下它的原始碼

"""
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,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': '','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>',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,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,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,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_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.

拋開其他的程式碼，我們之關注我們需要的東西

1 首先資料的驗證通過的是is_vaild方法，它下面有以下東西

return self.is_bound and not self.errors 對照以下也就是is_bound不能為空，並且 errors方法返回的為空，則通過驗證

2 我們找到 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()  #先賦一個空的錯誤字典
    if not self.is_bound: # Stop further processing.
      return
    self.cleaned_data = {}    #定義一個空的cleaned_data字典
    # If the form is permitted to be empty,short circuit any validation.
    if self.empty_permitted and not self.has_changed():
      return
#執行下面三種方法
    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(): #依次遍歷欄位
      # value_from_datadict() gets the data from the data dictionaries.
      # Each widget type knows how to retrieve its own data,initial)
        else:
          value = field.clean(value)
        self.cleaned_data[name] = value  #通過自定義和django裡面定義的方法後，將它加入到 cleand_data字典中
        if hasattr(self,'clean_%s' % name): #判斷是否有自定義的區域性鉤子函式
          value = getattr(self,'clean_%s' % name)() #通過了區域性鉤子則返回資料
          self.cleaned_data[name] = value  #將資料加入 cleaned_data
      except ValidationError as e:
        self.add_error(name,e) #錯誤的話執行 add_error

5 找到add_error

      self._errors[field].extend(error_list) #將錯誤資訊加入 _errors
      if field in self.cleaned_data:
        del self.cleaned_data[field] #刪除cleaned_data中這條資料，之前是通過自定義方法加入的，通不過 鉤子函式

6 回到上面執行 self._clean_form()

  def _clean_form(self):
    try:
      cleaned_data = self.clean() #接著執行 clean（）全域性鉤子
    except ValidationError as e:
      self.add_error(None,e)
    else:
      if cleaned_data is not None:
        self.cleaned_data = cleaned_data

7接著檢視 全域性鉤子 clean ，它只有一個返回的資料，因此我們可以自定義一個

  def clean(self):
    return self.cleaned_data #注意返回的資料和區域性鉤子的區別

8 最後檢視 _post_clean ，說白了就是什麼都沒有

def _post_clean(self):
    pass

以上是原始碼內部執行的順序，下面我們來看一個例子

1 自定義判斷欄位

2 自定義區域性鉤子

3自定義全域性鉤子

4 繼承並使用

5 .1在模板中顯示一

上面的程式碼 form_obj.errors.all_error 也可以改成 {{ form_obj.non_field_errors.0 }}

5.2 在模板中顯示二

6在瀏覽器上面看效果

其他：

我們在forms元件中處理的不同情況

希望本文所述對大家基於Django框架的Python程式設計有所幫助。