wtforms，在constru中生成字段

Question

我需要在表单的构造函数中生成字段，因为所需字段的数量可能会有所不同。我认为我目前的解决方案就是这个问题。当我试图扩展模板中的表单时，出现了一个异常

AttributeError:“UnboundField”对象没有属性“call”

这个代码有什么问题？在

class DriverTemplateSchedueForm(Form):
    def __init__(self, per_day=30, **kwargs):
        self.per_day = per_day
        ages = model.Agency.query.all()
        ages = [(a.id, a.name) for a in ages]
        self.days = [[[]] * per_day] * 7
        for d in range(7):
            for i in range(per_day):
                lbl = 'item_' + str(d) + '_' + str(i)
                self.__dict__[lbl] = SelectField(lbl, choices=ages)
                self.days[d][i] = self.__dict__[lbl]
        for day in self.days:
            print(day)

        Form.__init__(self, **kwargs)

Answer 1

修复

您需要将字段添加到类中，而不是添加到实例中：

def driver_template_schedue_form(ages, per_day=30, **kwargs):
    """Dynamically creates a driver's schedule form"""

    # First we create the base form
    # Note that we are not adding any fields to it yet
    class DriverTemplateScheduleForm(Form):
        pass

    # Then we iterate over our ranges
    # and create a select field for each
    # item_{d}_{i} in the set, setting each field
    # *on our **class**.
    for d in range(7):
        for i in range(per_day):
            label = 'item_{:d}_{:d}'.format(d, i)
            field = SelectField(label, choices=ages)
            setattr(DriverTemplateScheduleForm, label, field)

    # Finally, we return the *instance* of the class
    # We could also use a dictionary comprehension and then use
    # `type` instead, if that seemed clearer.  That is:
    # type('DriverTemplateScheduleForm', Form, our_fields)(**kwargs)
    return DriverTemplateScheduleForm(**kwargs)

为什么向self添加字段不起作用？

WTForms使用元类将表单和字段一起注册并保持顺序。*Field实例创建时没有绑定，added to the ^{} class' ^{} attribute，并绑定到类实例when the class is being constructed by the meta-class。在

当DriverTemplateScheduleForm.__init__运行时，_unbound_fields已经被填充。你可以把你的字段推到self._unbound_fields中，这样也可以工作，但这是使用私有API，因此以后可能会中断。在

Answer 2

关于元类的答案是正确的，但是如果你真的需要这个（像我一样）：

class SomeForm(Form):
    def __init__(self, *args, **kwargs):
        for name in kwargs.keys():
            if name.startswith('PREFIX_'):
                field = HiddenField()
                setattr(self, name, field)
                self._unbound_fields = self._unbound_fields + [[name, field]]
        super(SomeForm, self).__init__(*args, **kwargs)

请注意，我们不会修改_unbound_fields，下次也不会在表单类中包含此字段。在