import os
import re

#full path to folder containing the html files
mydir = "C:/downloads/Yuki/vg.tar/vg"

#REGEX of the string you want to search
prog = re.compile("(?i)(?<!not )an example string")

filelist = [ f for f in os.listdir(mydir) if f.endswith(".html") ]
for f in filelist:
    with open(os.path.join(mydir,f),encoding="utf8") as fc:
        if prog.search(fc.read()):
            fc.close()
            print ("Moving %s",f)
            os.rename(os.path.join(mydir,f), os.path.join("C:/downloads/Yuki/vg.tar/extracted",f))
            #full path of the folder where you want files to be moved