code: def transform_form_error(form, verbose=True):
      
      errors = []
      for field, err_msg in form.errors.items():
          if field == '__all__':  # general errors
              errors.append(', '.join(err_msg))
          else:                   # field errors
              field_name = field
              if verbose and field in form.fields:
                  field_name = form.fields[field].label or field
              errors.append('%s: %s' % (field_name, ', '.join(err_msg)))
      return errors
docs: transform form errors to list like
          ["field1: error1", "field2: error2"]