text: from __future__ import unicode_literals
  
  from django import forms
  from django.forms.util import flatatt
  from django.template import loader
  from django.utils.html import format_html, format_html_join
  from django.utils.http import int_to_base36
  from django.utils.safestring import mark_safe
  from django.utils.translation import ugettext, ugettext_lazy as _
  
  from django.contrib.auth import authenticate
  from django.contrib.auth.models import User
  from django.contrib.auth.hashers import UNUSABLE_PASSWORD, is_password_usable, identify_hasher
  from django.contrib.auth.tokens import default_token_generator
  from django.contrib.sites.models import get_current_site
  
  UNMASKED_DIGITS_TO_SHOW = 6
  
  mask_password = lambda p: "%s%s" % (p[:UNMASKED_DIGITS_TO_SHOW], "*" * max(len(p) - UNMASKED_DIGITS_TO_SHOW, 0))
  
  
  class ReadOnlyPasswordHashWidget(forms.Widget):
      def render(self, name, value, attrs):
          encoded = value
  
          if not is_password_usable(encoded):
              return "None"
  
          final_attrs = self.build_attrs(attrs)
  
          try:
              hasher = identify_hasher(encoded)
          except ValueError:
              summary = mark_safe("<strong>Invalid password format or unknown hashing algorithm.</strong>")
          else:
              summary = format_html_join('',
                                         "<strong>{0}</strong>: {1} ",
                                         ((ugettext(key), value)
                                          for key, value in hasher.safe_summary(encoded).items())
                                         )
  
          return format_html("<div{0}>{1}</div>", flatatt(final_attrs), summary)
  
  
  class ReadOnlyPasswordHashField(forms.Field):
      widget = ReadOnlyPasswordHashWidget
  
      def __init__(self, *args, **kwargs):
          kwargs.setdefault("required", False)
          super(ReadOnlyPasswordHashField, self).__init__(*args, **kwargs)
  
  
  class UserCreationForm(forms.ModelForm):
      """
      A form that creates a user, with no privileges, from the given username and
      password.
      """
      error_messages = {
          'duplicate_username': _("A user with that username already exists."),
          'password_mismatch': _("The two password fields didn't match."),
      }
      username = forms.RegexField(label=_("Username"), max_length=30,
          regex=r'^[\w.@+-]+$',
          help_text = _("Required. 30 characters or fewer. Letters, digits and "
                        "@/./+/-/_ only."),
          error_messages = {
              'invalid': _("This value may contain only letters, numbers and "
                           "@/./+/-/_ characters.")})
      password1 = forms.CharField(label=_("Password"),
          widget=forms.PasswordInput)
      password2 = forms.CharField(label=_("Password confirmation"),
          widget=forms.PasswordInput,
          help_text = _("Enter the same password as above, for verification."))
  
      class Meta:
          model = User
          fields = ("username",)
  
      def clean_username(self):
          # Since User.username is unique, this check is redundant,
          # but it sets a nicer error message than the ORM. See #13147.
          username = self.cleaned_data["username"]
          try:
              User.objects.get(username=username)
          except User.DoesNotExist:
              return username
          raise forms.ValidationError(self.error_messages['duplicate_username'])
  
      def clean_password2(self):
          password1 = self.cleaned_data.get("password1", "")
          password2 = self.cleaned_data["password2"]
          if password1 != password2:
              raise forms.ValidationError(
                  self.error_messages['password_mismatch'])
          return password2
  
      def save(self, commit=True):
          user = super(UserCreationForm, self).save(commit=False)
          user.set_password(self.cleaned_data["password1"])
          if commit:
              user.save()
          return user
  
  
  class UserChangeForm(forms.ModelForm):
      username = forms.RegexField(
          label=_("Username"), max_length=30, regex=r"^[\w.@+-]+$",
          help_text = _("Required. 30 characters or fewer. Letters, digits and "
                        "@/./+/-/_ only."),
          error_messages = {
              'invalid': _("This value may contain only letters, numbers and "
                           "@/./+/-/_ characters.")})
      password = ReadOnlyPasswordHashField(label=_("Password"),
          help_text=_("Raw passwords are not stored, so there is no way to see "
                      "this user's password, but you can change the password "
                      "using <a href=\"password/\">this form</a>."))
  
      def clean_password(self):
          return self.initial["password"]
  
      class Meta:
          model = User
  
      def __init__(self, *args, **kwargs):
          super(UserChangeForm, self).__init__(*args, **kwargs)
          f = self.fields.get('user_permissions', None)
          if f is not None:
              f.queryset = f.queryset.select_related('content_type')
  
  
  class AuthenticationForm(forms.Form):
      """
      Base class for authenticating users. Extend this to get a form that accepts
      username/password logins.
      """
      username = forms.CharField(label=_("Username"), max_length=30)
      password = forms.CharField(label=_("Password"), widget=forms.PasswordInput)
  
      error_messages = {
          'invalid_login': _("Please enter a correct username and password. "
                             "Note that both fields are case-sensitive."),
          'no_cookies': _("Your Web browser doesn't appear to have cookies "
                          "enabled. Cookies are required for logging in."),
          'inactive': _("This account is inactive."),
      }
  
      def __init__(self, request=None, *args, **kwargs):
          """
          If request is passed in, the form will validate that cookies are
          enabled. Note that the request (a HttpRequest object) must have set a
          cookie with the key TEST_COOKIE_NAME and value TEST_COOKIE_VALUE before
          running this validation.
          """
          self.request = request
          self.user_cache = None
          super(AuthenticationForm, self).__init__(*args, **kwargs)
  
      def clean(self):
          username = self.cleaned_data.get('username')
          password = self.cleaned_data.get('password')
  
          if username and password:
              self.user_cache = authenticate(username=username,
                                             password=password)
              if self.user_cache is None:
                  raise forms.ValidationError(
                      self.error_messages['invalid_login'])
              elif not self.user_cache.is_active:
                  raise forms.ValidationError(self.error_messages['inactive'])
          self.check_for_test_cookie()
          return self.cleaned_data
  
      def check_for_test_cookie(self):
          if self.request and not self.request.session.test_cookie_worked():
              raise forms.ValidationError(self.error_messages['no_cookies'])
  
      def get_user_id(self):
          if self.user_cache:
              return self.user_cache.id
          return None
  
      def get_user(self):
          return self.user_cache
  
  
  class PasswordResetForm(forms.Form):
      error_messages = {
          'unknown': _("That e-mail address doesn't have an associated "
                       "user account. Are you sure you've registered?"),
          'unusable': _("The user account associated with this e-mail "
                        "address cannot reset the password."),
      }
      email = forms.EmailField(label=_("E-mail"), max_length=75)
  
      def clean_email(self):
          """
          Validates that an active user exists with the given email address.
          """
          email = self.cleaned_data["email"]
          self.users_cache = User.objects.filter(email__iexact=email,
                                                 is_active=True)
          if not len(self.users_cache):
              raise forms.ValidationError(self.error_messages['unknown'])
          if any((user.password == UNUSABLE_PASSWORD)
                 for user in self.users_cache):
              raise forms.ValidationError(self.error_messages['unusable'])
          return email
  
      def save(self, domain_override=None,
               subject_template_name='registration/password_reset_subject.txt',
               email_template_name='registration/password_reset_email.html',
               use_https=False, token_generator=default_token_generator,
               from_email=None, request=None):
          """
          Generates a one-use only link for resetting password and sends to the
          user.
          """
          from django.core.mail import send_mail
          for user in self.users_cache:
              if not domain_override:
                  current_site = get_current_site(request)
                  site_name = current_site.name
                  domain = current_site.domain
              else:
                  site_name = domain = domain_override
              c = {
                  'email': user.email,
                  'domain': domain,
                  'site_name': site_name,
                  'uid': int_to_base36(user.id),
                  'user': user,
                  'token': token_generator.make_token(user),
                  'protocol': use_https and 'https' or 'http',
              }
              subject = loader.render_to_string(subject_template_name, c)
              # Email subject *must not* contain newlines
              subject = ''.join(subject.splitlines())
              email = loader.render_to_string(email_template_name, c)
              send_mail(subject, email, from_email, [user.email])
  
  
  class SetPasswordForm(forms.Form):
      """
      A form that lets a user change set his/her password without entering the
      old password
      """
      error_messages = {
          'password_mismatch': _("The two password fields didn't match."),
      }
      new_password1 = forms.CharField(label=_("New password"),
                                      widget=forms.PasswordInput)
      new_password2 = forms.CharField(label=_("New password confirmation"),
                                      widget=forms.PasswordInput)
  
      def __init__(self, user, *args, **kwargs):
          self.user = user
          super(SetPasswordForm, self).__init__(*args, **kwargs)
  
      def clean_new_password2(self):
          password1 = self.cleaned_data.get('new_password1')
          password2 = self.cleaned_data.get('new_password2')
          if password1 and password2:
              if password1 != password2:
                  raise forms.ValidationError(
                      self.error_messages['password_mismatch'])
          return password2
  
      def save(self, commit=True):
          self.user.set_password(self.cleaned_data['new_password1'])
          if commit:
              self.user.save()
          return self.user
  
  
  class PasswordChangeForm(SetPasswordForm):
      """
      A form that lets a user change his/her password by entering
      their old password.
      """
      error_messages = dict(SetPasswordForm.error_messages, **{
          'password_incorrect': _("Your old password was entered incorrectly. "
                                  "Please enter it again."),
      })
      old_password = forms.CharField(label=_("Old password"),
                                     widget=forms.PasswordInput)
  
      def clean_old_password(self):
          """
          Validates that the old_password field is correct.
          """
          old_password = self.cleaned_data["old_password"]
          if not self.user.check_password(old_password):
              raise forms.ValidationError(
                  self.error_messages['password_incorrect'])
          return old_password
  PasswordChangeForm.base_fields.keyOrder = ['old_password', 'new_password1',
                                             'new_password2']
  
  
  class AdminPasswordChangeForm(forms.Form):
      """
      A form used to change the password of a user in the admin interface.
      """
      error_messages = {
          'password_mismatch': _("The two password fields didn't match."),
      }
      password1 = forms.CharField(label=_("Password"),
                                  widget=forms.PasswordInput)
      password2 = forms.CharField(label=_("Password (again)"),
                                  widget=forms.PasswordInput)
  
      def __init__(self, user, *args, **kwargs):
          self.user = user
          super(AdminPasswordChangeForm, self).__init__(*args, **kwargs)
  
      def clean_password2(self):
          password1 = self.cleaned_data.get('password1')
          password2 = self.cleaned_data.get('password2')
          if password1 and password2:
              if password1 != password2:
                  raise forms.ValidationError(
                      self.error_messages['password_mismatch'])
          return password2
  
      def save(self, commit=True):
          """
          Saves the new password.
          """
          self.user.set_password(self.cleaned_data["password1"])
          if commit:
              self.user.save()
          return self.user
  