from wtforms.form import Form
# 引入Form元素父类
from wtforms import StringField
# 引入Form验证父类
from wtforms.validators import DataRequiredclass LoginForm(Form):name = StringField(label='姓名',validators=[DataRequired('不能为空！')],render_kw={'placeholder': '请输入姓名！'})

def with_metaclass(meta, base=object):#返回一个类NewBase并且继承BaseForm,类似于:#class NewBase(BaseForm):#   passreturn meta("NewBase", (base,), {})

class Form(with_metaclass(FormMeta, BaseForm)):pass

class FormMeta(type):def __init__(cls, name, bases, attrs):#这里会执行type.__init__()，初始化类NewBase类，#现在的cls为NewBasetype.__init__(cls, name, bases, attrs)#给NewBase设置属性：初始值为空cls._unbound_fields = Nonecls._wtforms_meta = None

class LoginForm(Form):name = StringField(label='姓名',validators=[DataRequired('不能为空！')],render_kw={'placeholder': '请输入姓名！'})   

@home.route('/')
def index():form = LoginForm()return render_template('login.html', form=form)

class FormMeta(type):def __call__(cls, *args, **kwargs):if cls._unbound_fields is None:#判断如果_unbound_fields为空fields = []for name in dir(cls):#或者该类的所有的属性if not name.startswith('_'):#遍历所有的名字，如果不是以下滑线开头,获取到给unbound_field赋值:unbound_field = getattr(cls, name)if hasattr(unbound_field, '_formfield'):#筛选真正需要的LoginForm字段
                          fields.append((name, unbound_field))#对要渲染的字段进行排序，所以字段前端字段的渲染有顺序fields.sort(key=lambda x: (x[1].creation_counter, x[0]))#将获取到的fields赋值给_unbound_fieldscls._unbound_fields = fieldsif cls._wtforms_meta is None:bases = []for mro_class in cls.__mro__:if 'Meta' in mro_class.__dict__:#mro_class是<class 'wtforms.form.Form'>#mro_class.Meta是<class 'wtforms.meta.DefaultMeta'>
                  bases.append(mro_class.Meta)#这里创建了Meta类并赋值给cls._wtforms_metacls._wtforms_meta = type('Meta', tuple(bases), {})#这里调用__call__时调用了Form的__init__方法return type.__call__(cls, *args, **kwargs)

class Form(with_metaclass(FormMeta, BaseForm)):def __init__(self, formdata=None, obj=None, prefix='', data=None, meta=None, **kwargs):meta_obj = self._wtforms_meta()#这里又调用了父类的初始化方法super(Form, self).__init__(self._unbound_fields, meta=meta_obj, prefix=prefix)

class BaseForm(object):def __init__(self, fields, prefix='', meta=DefaultMeta()):self._fields = OrderedDict()for name, unbound_field in itertools.chain(fields, extra_fields):#循环遍历fields,self._fields中有所有的字段options = dict(name=name, prefix=prefix, translations=translations)field = meta.bind_field(self, unbound_field, options)##OrderedDict([('name', <wtforms.fields.core.StringField object at 0x0000006A6240A438>)])self._fields[name] = field

class Form(with_metaclass(FormMeta, BaseForm)):def __init__(self, formdata=None, obj=None, prefix='', data=None, meta=None, **kwargs):meta_obj = self._wtforms_meta()if meta is not None and isinstance(meta, dict):meta_obj.update_values(meta)super(Form, self).__init__(self._unbound_fields, meta=meta_obj, prefix=prefix)#上述代码已经跑完，现在开始从这里执行代码，这里的self._fields有自定义的Form中的所有的字段for name, field in iteritems(self._fields):setattr(self, name, field)#此时执行self.process方法，自己这里没process方法，然后就去基类中执行，这时程序跳到了BaseForm中的process方法self.process(formdata, obj, data=data, **kwargs)

class BaseForm(object):def process(self, formdata=None, obj=None, data=None, **kwargs):formdata = self.meta.wrap_formdata(self, formdata)if data is not None:kwargs = dict(data, **kwargs)#因为formdata和data都为None所以程序执行到了这里:for name, field, in iteritems(self._fields):if obj is not None and hasattr(obj, name):field.process(formdata, getattr(obj, name))elif name in kwargs:field.process(formdata, kwargs[name])else:#最后执行到这里，这是调用process是调用了字段对象StringField的process方法，自己没有这个方法跑到了Field中去:field.process(formdata)

class Field(object):def process(self, formdata, data=unset_value):self.process_errors = []if data is unset_value:try:data = self.default()except TypeError:data = self.defaultself.object_data = datatry:#调用该方法为了处理适用于该字段对象的值并保存结果。
            self.process_data(data)except ValueError as e:self.process_errors.append(e.args[0])#由于formdata，self.filters字段为空，下段代码不执行。if formdata:try:if self.name in formdata:self.raw_data = formdata.getlist(self.name)else:self.raw_data = []self.process_formdata(self.raw_data)except ValueError as e:self.process_errors.append(e.args[0])try:for filter in self.filters:self.data = filter(self.data)except ValueError as e:self.process_errors.append(e.args[0])

class LoginForm(Form):name = StringField(label='姓名',validators=[DataRequired('不能为空！')],render_kw={'placeholder': '请输入姓名！'})

class StringField(Field):#这里实例化一个控件，接着我们看下TextInput()里面做了什么？widget = widgets.TextInput()class TextInput(Input):#这个类加括号调用了基类的__call__方法，我们看下基类：input_type = 'text'class Input(object):#我们看到这里渲染了html标签并返回def __call__(self, field, **kwargs):kwargs.setdefault('id', field.id)kwargs.setdefault('type', self.input_type)if 'value' not in kwargs:#这里会调用_value()给相关标签添加一个'value='的html属性kwargs['value'] = field._value()return HTMLString('<input %s>' % self.html_params(name=field.name, **kwargs))

#我们看下基类
class Field(object):def __str__(self):#返回了一个代表html的对象，加括号，又调用了__call__()return self()def __call__(self, **kwargs):#关键代码，我们接着看下render_fieldreturn self.meta.render_field(self, kwargs)
#这里来到了meta.py
class DefaultMeta(object):def render_field(self, field, render_kw):#这里控制render的实现，默认调用field.widget(field, **render_kw)other_kw = getattr(field, 'render_kw', None)if other_kw is not None:render_kw = dict(other_kw, **render_kw)#接着调用StringField的静态字段对控件进行最终的渲染return field.widget(field, **render_kw)

class Field(object)def __new__(cls, *args, **kwargs):if '_form' in kwargs and '_name' in kwargs:return super(Field, cls).__new__(cls)else:#返回一个UnboundField对象,对StringField的对象内容进行了封装，实例化UnboundField调用\__init__return UnboundField(cls, *args, **kwargs)#看下UnboundField的执行流程：
class UnboundField(object):_formfield = True#首先这里的计数，是根据字段的书写顺序进行的加减，为了排序使用creation_counter = 0#现在的self:<UnboundField(StringField, (), {'label': '姓名', 'validators': [<wtforms.validators.DataRequired object at 0x0000009A20B948D0>], 'render_kw': {'placeholder': '请输入姓名！'}})>def __init__(self, field_class, *args, **kwargs):UnboundField.creation_counter += 1self.field_class = field_classself.args = argsself.kwargs = kwargsself.creation_counter = UnboundField.creation_counter

@home.route('/')
def index():form = LoginForm()return render_template('login.html', form=form)

class FormMeta(type):def __call__(cls, *args, **kwargs):if cls._unbound_fields is None:fields = []for name in dir(cls):if not name.startswith('_'):unbound_field = getattr(cls, name)if hasattr(unbound_field, '_formfield'):#fields里有username对应的UnboundField
                        fields.append((name, unbound_field))#对field进行了排序，字段的先后顺序决定了页面的显示顺序fields.sort(key=lambda x: (x[1].creation_counter, x[0]))#现在_unbound_fields 中有所有的字段cls._unbound_fields = fieldsif cls._wtforms_meta is None:bases = []for mro_class in cls.__mro__:if 'Meta' in mro_class.__dict__:bases.append(mro_class.Meta)#创建了一个Meta类继承<class 'list'>: [<class 'wtforms.meta.DefaultMeta'>]cls._wtforms_meta = type('Meta', tuple(bases), {})return type.__call__(cls, *args, **kwargs)

class Form(with_metaclass(FormMeta, BaseForm)):def __init__(self, formdata=None, obj=None, prefix='', data=None, meta=None, **kwargs):#得到一个DefaultMeta的对象meta_obj = self._wtforms_meta()#这里又执行了父类BaseForm的__init__()方法super(Form, self).__init__(self._unbound_fields, meta=meta_obj, prefix=prefix)#这句话的意思是给每个字段对象设置一个属性，可以obj.attr获取值for name, field in iteritems(self._fields):setattr(self, name, field)#这里去处理数据，校验数据self.process(formdata, obj, data=data, **kwargs)

class BaseForm(object):def __init__(self, fields, prefix='', meta=DefaultMeta()):self._fields = OrderedDict()#遍历循环fieldsfor name, unbound_field in itertools.chain(fields, extra_fields):options = dict(name=name, prefix=prefix, translations=translations)#这里将所有Fields实例化完毕field = meta.bind_field(self, unbound_field, options)#将值赋给_fieldsself._fields[name] = field

class DefaultMeta(object):def bind_field(self, form, unbound_field, options):#这里又跑到了UnboundField类中执行bind方法return unbound_field.bind(form=form, **options)

class UnboundField(object):#看下关键参数，别的就不需要看了:#form=<app.home.forms.LoginForm object at 0x000000DE0AEA9EF0>#name='username'def bind(self, form, name, prefix='', translations=None, **kwargs):kw = dict(self.kwargs,_form=form,_prefix=prefix,_name=name,_translations=translations,**kwargs)#这里去创建StringFiled类并实例化return self.field_class(*self.args, **kw)

class Field(object):def __new__(cls, *args, **kwargs):if '_form' in kwargs and '_name' in kwargs:#现在kwargs中有值，创建一个类:return super(Field, cls).__new__(cls)else:#这个是刚开始加载到内存时,刚开始创建Field类时会返回UnboundField:return UnboundField(cls, *args, **kwargs)#创建完后去初始化这个类得到StringFiled对象:def __init__(self, label=None, validators=None, filters=tuple(),description='', id=None, default=None, widget=None,render_kw=None, _form=None, _name=None, _prefix='',_translations=None, _meta=None):

class Form(with_metaclass(FormMeta, BaseForm)):def __init__(self, formdata=None, obj=None, prefix='', data=None, meta=None, **kwargs):#主要去处理数据，调用了基类的self.process方法，看下面：self.process(formdata, obj, data=data, **kwargs)class BaseForm(object):def process(self, formdata=None, obj=None, data=None, **kwargs):#这时调用了字段自己的process方法，
         field.process(formdata)class Field(object):def process(self, formdata, data=unset_value):#这里的self指Field子类对象
        self.process_data(data)
#这里处理了数据
def process_data(self, value):self.data = value