Python Flask WTForms FloatField allow 1,0 and 1.0 allow comma and dot

Question

I have a flask app where a user can submit a room. There is a price field which is a FloatField in my WTForms:

preis = FloatField('Preis p.P.', validators=[Optional()])

If the input is correct (with a dot) it works fine, example:

1.00

But if a comma is used it triggers an error, example:

1,00

My Idea was to catch this in my main.py, but the problem is that the default error message from WTForms triggers first:

I tried to convert the float to string, check if , is in this string and use a simple replace(",",".") and then convert back to float.

An other side question, how do I change this default Not a valid float value message to a custom message?

Thanks!

Asked By: Roman

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Source

Answer 1

You can subclass FloatField and add the replace function to its process_formdata() function.

class MyFloatField(FloatField):
    def process_formdata(self, valuelist):
        if valuelist:
            try:
                self.data = float(valuelist[0].replace(',', '.'))
            except ValueError:
                self.data = None
                raise ValueError(self.gettext('Not a valid float value'))

Here you can also change the Error message.

Answered By: MrLeeh

Answer 2

I would like to suggest use of DecimalField instead of FloatField

It will let you avoid taking care of dots and commas.

i.e.:

preis = DecimalField('Preis p.P.', places=2, validators=[Optional()])

I also attach a small hint from https://wtforms.readthedocs.io/en/3.0.x/fields/#basic-fields

class wtforms.fields.DecimalField(default field arguments, places=2,
rounding=None, use_locale=False, number_format=None)[source]

Answered By: Markus Wanx

Python Flask WTForms FloatField allow 1,0 and 1.0 allow comma and dot

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