<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def addFilter(self, field, value):
 """Add a filter to the seach. :param field: what field filter (see GitHub search). :type field: str. :param value: value of the filter (see GitHub search). :type value: str. """

        if "<" not in value or ">" not in value or ".." not in value:
            value = ":" + value

        if self.__urlFilters:
            self.__urlFilters += "+" + field + str(quote(value))
        else:
            self.__urlFilters += field + str(quote(value))