Bidirectional form data filters

I use a custom filter to add the currency prefix to a FloatField to make it more user friendly. This also adds the currency prefix to the value in my edit form.

from app import app

@app.template_filter()
def format_currency(value:float, currency:str=None):
    if currency == 'AUD':
        return "AU${:,.2f}".format(value)
    else:
        return "${:,.2f}".format(value)


from app._filters import format_currency

class ContractForm(Form):
    cost = FloatField('Cost', id='contract_cost', default=0.00, filters=[format_currency])

Is it possible (and how would one implement) to use a filter to remove the currency prefix from the field data on submit before form validation?

I have gone through documentation and searched forums but haven't found a solution.

Start by reading the FloatField usage and the custom filter in app/_filters.py, then trace when filters run relative to form submission and validation. Determine whether the currency prefix can be removed before FloatField validation while preserving the existing formatted display value. Done means a submitted prefixed currency value is accepted and validated as a number without breaking the edit-form output.