注意：重写钩子方法时方法名为 - clena_字段名(self): 即可

from django import forms
from django.core.exceptions import ValidationError
from jax import models
 
 
class RegForm(forms.Form):
    username = forms.CharField(
        max_length=16,
        label="用户名",
        error_messages={
            "max_length": "用户名最长16位",
            "required": "用户名不能为空!",
        },
        widget=forms.TextInput(
            attrs={"class":"form-control", "placeholder": "用户名"},
        )
    )
 
    password = forms.CharField(
        min_length=6,
        label="密码",
        error_messages={
            "required": "密码不能为空",
            "min_length": "密码不能少于6位",
        },
        widget = forms.PasswordInput(
            attrs={"class": "form-control", "placeholder": "密码"},
        )
    )
 
    re_password = forms.CharField(
        min_length=6,
        label="确认密码",
        error_messages={
            "required": "密码不能为空",
            "min_length": "密码不能少于6位",
        },
        widget=forms.PasswordInput(
            attrs={"class": "form-control", "placeholder": "密码"},
        )
    )
 
    email = forms.EmailField(
        label="邮箱",
        error_messages={
            "invalid": "请输入正确的邮箱格式",
            "required": "邮箱不能为空",
        },
        widget=forms.EmailInput(
            attrs={"class": "form-control", "placeholder": "邮箱"},
        )
    )
 
    # 重写全局的钩子函数，对确认密码做校验
    def clean(self):
        password = self.cleaned_data.get("password")
        re_password = self.cleaned_data.get("re_password")
 
        if re_password and re_password != password:
            self.add_error("re_password", ValidationError("两次密码不一致"))
 
        else:
            return self.cleaned_data
 
    # 重写username局部钩子
    def clean_username(self):
        username = self.cleaned_data.get("username")
        is_exist = models.UserInfo.objects.filter(username=username)
        if is_exist:
            self.add_error("username", ValidationError("该用户已经存在！"))
        else:
            return username
 
    # 重写email局部钩子
    def clean_email(self):
        email = self.cleaned_data.get("email")
        is_exist = models.UserInfo.objects.filter(email=email)
        if is_exist:
            self.add_error("email", ValidationError("该邮箱已经注册！"))
        else:
            return email

django的form表单中定义的字段，都有对应的id以及方法，例如id_username、clean_username，这里的方法均为django中forms.Form源码类BaseForm定义

例：

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 = {} if data is None else data
        self.files = {} if files is None else files
        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)
 
 
    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(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):
        """Return True if data differs from initial."""
        return bool(self.changed_data)