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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def format(self, fmt):
 """Returns string representing the items specified in the format string The format string can contain: .. code:: d - drive letter p - path n - name x - extension z - file size t - file time in seconds And, you can string them together, e.g. `dpnx` returns the fully qualified name. On platforms like Unix, where drive letter doesn't make sense, it's simply ignored when used in a format string, making it easy to construct fully qualified path names in an os independent manner. Parameters fmt : str A string representing the elements you want returned. Returns ------- str A string containing the elements of the path requested in `fmt` """


        val = ''
        for x in fmt:
            if x == 'd':
                val += self._driv

            elif x == 'p':
                val += self._path

            elif x == 'n':
                val += self._name

            elif x == 'x':
                val += self._ext

            elif x == 'z':
                if self._size != None: val += str(self._size)

            elif x == 't':
                if self._time != None: val += str(self._time)

        return val