string and text handling character(sdescription interprets the letters " "" "" "" "" "" "and "xas flag settings corresponding to the re are ire lre mre sre ure flag settings given to re compile("aonly available in python (?matches the regular expression inside the parentheses but discards the matched substring (? matches the regular expression in the parentheses and creates named group the group name must be valid python identifier (? =namematches the same text that was matched by an earlier named group (? comment the contents of the parentheses are ignored (?matches the preceding expression only if followed by the pattern in the parentheses for exampler'hello (?=world)matches 'hello only if followed by 'world(?matches the preceding expression only if it' not followed by the pattern in parentheses for exampler'hello (?!world)matches 'hello only if it' not followed by 'world(?<matches the following expression if it' preceded by match of the pattern in parentheses for exampler'(?<=abc)defmatches 'defonly if it' preceded by 'abc(?<matches the following expression only if it' not preceded by match of the pattern in parentheses for exampler'(?<!abc)defmatches 'defonly if it' not preceded by 'abc(?(id|name)ypat|npatchecks to see whether the regular expression group identified by id or name exists if sothe regular expression ypat is matched if notthe optional expression npat is matched for examplethe pattern '(hello)?(?( world|howdy)matches the string 'hello worldor the string 'howdy(?ailmsuxstandard character escape sequences such as '\nand '\tare recognized as standard characters in regular expression (for exampler'\ +would match one or more newline charactersin additionliteral symbols that normally have special meaning in regular expression can be specified by preceding them with backslash for exampler'\*matches the character in additiona number of backslash sequences correspond to special sets of characterscharacter(sdescription \number matches the text that was matched by previous group number groups are numbered from to starting from the left matches only at the start of the string matches the empty string at the beginning or end of word word is sequence of alphanumeric characters terminated by whitespace or any other nonalphanumeric character \ \ lib fl ff