str1="2017-10-15 this is happy day..." >>> re.sub("(\d{4})-(\d{2})-(\d{2})",r"\2/\3/\1",str1) ##'10/15/2017 this is happy day...' >>> re.sub("(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})",r"\g<month>/\g<day>/\g<year>",str1) #'10/15/2017 this is happy day...'
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