human
Solve the following python programming problem given the following code:
@ staticmethod 
def _generate_urls_for_elements(elements) : 
    ' Static method for generating urls from a list of urls_sugar
        elements.
        ' 
    def __generate(elements) : 
        ' Recursive support function.
            ' 
        new_urls = [[]] 
        for elem in elements : 
            if isinstance (elem, (Constant, Variable)) : 
                sub_urls = elem.get_regexp () 
                if (not isinstance (sub_urls, list)) : 
                    sub_urls = [sub_urls] 
new_urls = [(x + [((elem.prefix + y) + elem.suffix)]) for x in new_urls for y in sub_urls] 
else : 
                if isinstance (elem, Optional) : 
                    sub_urls = __generate (elem.args) 
                    new_urls.extend ([(x + y) for x in new_urls for y in sub_urls]) 
return new_urls 
return [('^%s$' % ''.join (x)) for x in __generate (x)] 

    
    

    Fix the buggy line: return [('^%s$' % ''.join (x)) for x in __generate (x)]
assistant
#Here is Python program to fix the buggy line: return [('^%s$' % ''.

return [('^%s$' % ''.join (x)) for x in __generate (elements)]