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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 startPrefixMapping(self, prefix, uri, *, auto=False):
 """ Start a prefix mapping which maps the given `prefix` to the given `uri`. Note that prefix mappings are handled transactional. All announcements of prefix mappings are collected until the next call to :meth:`startElementNS`. At that point, the mappings are collected and start to override the previously declared mappings until the corresponding :meth:`endElementNS` call. Also note that calling :meth:`startPrefixMapping` is not mandatory; you can use any namespace you like at any time. If you use a namespace whose URI has not been associated with a prefix yet, a free prefix will automatically be chosen. To avoid unneccessary performance penalties, do not use prefixes of the form ``"ns{:d}".format(n)``, for any non-negative number of `n`. It is however required to call :meth:`endPrefixMapping` after a :meth:`endElementNS` call for all namespaces which have been announced directly before the :meth:`startElementNS` call (except for those which have been chosen automatically). Not doing so will result in a :class:`RuntimeError` at the next :meth:`startElementNS` or :meth:`endElementNS` call. During a transaction, it is not allowed to declare the same prefix multiple times. """

        if     (prefix is not None and
                (prefix == "xml" or
                 prefix == "xmlns" or
                 not xmlValidateNameValue_str(prefix) or
                 ":" in prefix)):
            raise ValueError("not a valid prefix: {!r}".format(prefix))

        if prefix in self._ns_prefixes_floating_in:
            raise ValueError("prefix already declared for next element")
        if auto:
            self._ns_auto_prefixes_floating_in.add(prefix)
        self._ns_prefixes_floating_in[prefix] = uri
        self._ns_decls_floating_in[uri] = prefix