I assume that your problem is that when the data is posted , the ORM when submitting it to the database throws the eror.
You need to place the posted value into a variable and use a python replace statement to replace the , with a period.
Not sure what type of validation that you are using.
Putting aside any sort of validation on the number.
number=new_number.replace(" , " , " . ")
Then the database won't complain