BeautifulSoup处理空行

def bs_preprocess(html):
     """remove distracting whitespaces and newline characters"""
     pat = re.compile('(^[\s]+)|([\s]+$)', re.MULTILINE)
     html = re.sub(pat, '', html)       # remove leading and trailing whitespaces
     html = re.sub('\n', ' ', html)     # convert newlines to spaces
                                        # this preserves newline delimiters
     html = re.sub('[\s]+<', '<', html) # remove whitespaces before opening tags
     html = re.sub('>[\s]+', '>', html) # remove whitespaces after closing tags
     return html