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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 _safe_id(self, idstring):
 """Make a string safe for including in an id attribute. The HTML spec says that id attributes 'must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".")'. These regexps are slightly over-zealous, in that they remove colons and periods unnecessarily. Whitespace is transformed into underscores, and then anything which is not a hyphen or a character that matches \w (alphanumerics and underscore) is removed. """

        # Transform all whitespace to underscore
        idstring = re.sub(r'\s', "_", '%s' % idstring)
        # Remove everything that is not a hyphen or a member of \w
        idstring = re.sub(r'(?!-)\W', "", idstring).lower()
        return idstring