name = ['a', 'b', 'c']
for input_name in names:
    field = forms.CharField(widget=DimensionsWidget(dimensions), required=False)

    def wrapper(field_name):

        def clean_dimensions(self):
            """
            Dimensions field clean method
            """
            # field_name == 'c' - ALWAYS!! :(
            value = self[field_name].value()
            try:
                for i in value:
                    int(i)
            except ValueError as e:
                raise ValidationError(self.error_messages['invalid_int'] + unicode(e))
        return clean_dimensions

    # monkey-patch the clean method for this field
    setattr(self, 'clean_' + input_name, types.MethodType(wrapper(input_name), self))