Flask-WTF FloatField非数值输入触发DataRequired而非类型错误排查

我给FloatField添加了DataRequired()和自定义验证器validate_someNumber，字段需满足以下要求：

• 必须填写数据
• 仅允许单个数值
• 整数部分最大为999
• 仅允许一位小数（如999.9）

相关代码 #

form.py #

from flask_wtf import FlaskForm
from wtforms import FloatField
from wtforms.validators import DataRequired
from validators import validate_someNumber

class MyForm(FlaskForm):
    someNumber = FloatField('Some Number', validators=[DataRequired(), validate_someNumber])

validators.py（自定义验证器） #

from wtforms.validators import ValidationError

def validate_someNumber(form, field):
    if field.data is not None:
        whole_number = int(field.data)
        decimal_places = len(str(field.data).split('.')[1]) if '.' in str(field.data) else 0
        if whole_number > 999 or decimal_places > 1:
            raise ValidationError('Some Number must be less than or equal to 999 and have only one decimal place')

模板文件：someTemplate.html #

<form method="POST" action="{{ url_for('someTemplate') }}">
    <div>
        <label for="{{ form.someNumber.id }}">{{ form.weight.label }}</label>
        {{ form.someNumber }}
    </div>
    {% for error in form.someNumber.errors %}
    <div class="alert alert-danger">
        {{ error }} debugging info: {{ form.someNumber.data }}
    </div>
    {% endfor %}
</form>

路由代码（app.py） #

@app.route("/someTemplate", methods=['GET', 'POST'])
def someTemplate():
    form = MyForm()
    if form.validate_on_submit():
        flash(f"You have submitted an entry", "success")
        print(form.data)
        return render_template("someTemplate.html", form=form)
    return render_template("someTemplate.html", form=form)

遇到的问题 #

1. 输入totallyNotNumeric这类非数值内容时，页面显示的是*DataRequired()*的提示信息「This field is required」，而非预期的类型错误提示。但测试未添加任何验证器的FloatField时，输入非数值会正常显示类型错误。
2. 自定义验证器对111.111这类输入能正常触发自定义错误提示，但在验证器中加入类型判断（如下代码）后完全无效：

if field.data is not None:
    whole_number = None
    decimal_places = None
    if isinstance(field.data, (int, float)):
        whole_number = int(field.data)
        decimal_places = len(str(field.data).split('.')[1]) if '.' in str(field.data) else 0
     else:
        raise ValidationError('someNumber must be a number')

    if whole_number > 999 or decimal_places > 1:
        raise ValidationError('someNumber must be less than or equal to 999 and have only one decimal place')

希望得到排查建议，确认是否遗漏了Flask-WTF/WTForms的核心概念。

内容的提问来源于stack exchange，提问作者null-point-exceptional