class SignupForm(forms.Form):
  username = forms.CharField(validators=[user_unique_validate, username_rule_validate, ], required=True,
                max_length=30, min_length=5,
                error_messages={'required': '用户名不能为空', 'max_length': '用户名至少5位',
                        'min_length': '用户名最多30位'})
  password = forms.CharField(min_length=6, max_length=50, required=True,
                error_messages={'required': '密码不能为空',
                        'invalid': '密码格式错误',
                        'min_length': '密码不能少于6位',
                        'max_length': '密码最多50位'})
  classInfo = forms.ModelChoiceField(queryset=ClassInfo.objects.all(), required=True, empty_label=None, initial="预设值")#这里加的是班级名字
  email = forms.EmailField(validators=[email_unique_validate, ], required=True,
               error_messages={'required': '邮箱不能为空', 'invalid': '邮箱格式错误'})
  mobile = forms.CharField(validators=[mobile_validate, ], required=True,
               error_messages={'required': '手机号不能为空'})

class SignupView(View):
  def get(self, request):
    obj = SignupForm()
    return render(request, 'user/signup.html', locals())

<tr><th><label for="id_username">Username:</label></th><td><input type="text" name="username" value="123123" minlength="5" maxlength="30" required id="id_username"></td></tr>
<tr><th><label for="id_password">Password:</label></th><td><input type="text" name="password" value="213123" minlength="6" maxlength="50" required id="id_password"></td></tr>
<tr><th><label for="id_classInfo">Classinfo:</label></th><td>
<select name="classInfo" id="id_classInfo">
 <option value="1" selected>15医药软件</option>
 <option value="2">15医药信息</option>
</select></td></tr>
<tr><th><label for="id_email">Email:</label></th><td><input type="email" name="email" value="123123231@qq.com" required id="id_email"></td></tr>
<tr><th><label for="id_mobile">Mobile:</label></th><td><input type="text" name="mobile" value="13328768123" required id="id_mobile"></td></tr>

<form method="post" action="{% url 'signup' %}">
  ...
  {% for field in obj %}
    {{ field }}
  {% end for %}
  ...
</form>

<form method="post" action="{% url 'signup' %}>
....
   <tr>
     <td width="120" align="right" valign="top">用户名(学号)</td>
     <td width="auto" align="left"><input type="text" name="username" class="sls">        </td>
   </tr>
   <tr>
     <td width="120" align="right">密码</td>
     <td width="auto" align="left"><input type="password" name="password" class="sls"></td>
   </tr>
   <tr>
     <td width="120" align="right" valign="top">电子邮件</td>
     <td width="auto" align="left"><input type="text" name="email" class="sls"></td>
   </tr>
   <tr>
     <td width="120" align="right">班级</td>
     <td width="auto" align="left">
        {{ obj.classInfo }}
     </td>
   </tr>
   <tr>
     <td width="120" align="right" valign="top">手机号</td>
     <td width="auto" align="left"><input type="text" class="sls" name="mobile"></td>
   </tr>
....

  def post(self, request):
    has_error = True
    obj = SignupForm(request.POST)
    #print(obj)
    if obj.is_valid():
      has_error = False
      username = obj.cleaned_data['username']
      password = obj.cleaned_data['password']
      class_name = obj.cleaned_data['classInfo']
      email = obj.cleaned_data['email']
      mobile = obj.cleaned_data['mobile']
  ......