class LoginForm(forms.Form):

    username = forms.CharField(max_length=20,min_length=3,label='用户名',error_messages={

                    'required':'用户名不能为空！',

                    'invalid':'格式错误！',

                    'max_length':'用户名长度超限！',

                    'min_length':'用户名过短！'

                                }

        ,widget=forms.widgets.TextInput(attrs={'class':'form-control','style':'width:300px'})

                               )

    password = forms.CharField(max_length=18,min_length=3,label='密码',error_messages={

        'required':'密码不能为空！',

        'invalid':'格式错误！',

        'max_length':'密码长度超限！',

        'min_length':'密码长度过短！',

    }

        ,widget=forms.widgets.PasswordInput(attrs={'class':'form-control','style':'width:300px'})

                               )

    def clean_username(self):

        username = self.cleaned_data.get("username")   # 错将这里的username写掉了一个字母

        if username[0].isdigit():

            self.add_error('username','用户名不能以数字开头！')

        return username

    def clean_password(self):

        password = self.cleaned_data.get("password")

        if password == '':

            self.add_error('password','密码过于简单!')

        return password

def login(request):

    form_obj = LoginForm()

    if request.method == "POST":

        form_obj = LoginForm(request.POST)

            print(form_obj.clean_data)

#结果：{'username': None, 'password': '1234',}

    def clean_username(self):

        username = self.cleaned_data.get("username")   # 错将这里的username写掉了一个字母

        if username[0].isdigit():

            self.add_error('username','用户名不能以数字开头！')

　　　　　　return username    # 这里必须return 回去   不然clean_data里面的username的值就是None