Flask wtforms DataRequired validator tiggers (instead of custom or default validator) when wrong data type submitted as input

Trying to attach a DataRequired() and custom validator, validate_someNumber to a FloatField. But I am having a hard time understanding the feedback from the form field errors when the validation errors are raised. Here are my requirements for the field in question:

• There should be data
• The field should only allow a single numeric value
• The field should only allow a maximum whole number placement to the hundred's. ex: maximum 999
• The field should only allow a single decimal place. ex: 999.9

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])

validator

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')

flask template

<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>

And finally my route

@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)

Then I try to submit input like "totallyNotNumeric" and the UI renders the DataRequired warning message, "This field is required". Why would it not raise the "This is not a valid float" message instead?

That seems to be the message closest to the field Class. I tested a plain FloatField without validators and it passed the '... not a valid float' message to the errors list when I tried using alpha-numeric input???

Furthermore, I noticed my custom validator works. When entering something like, "111.111". I get my custom error message. So I thought let me try validating the data type in my custom validator as well. So I modified it like this:

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')

This did not work. Any advice? Am I missing something super simple or misunderstanding a core concept of flask forms? wtforms? Thanks

There is no specific reason to use the DataRequired validator here. When used, previous errors (e.g. processing errors) are removed from the field if the data is empty.
Change from DataRequired to InputRequired and it should give you the familiar error message "This is not a valid float".