python regex note

　　To remember python regex easily, we organise python regex notes from concrete to abstract, and from simple to sophisticated.

I, Important character:

　　1, Quantitive character:

　　　　? :[0,1], 　　*:[0,infi),　　+:(0,infi),　　{n}:[n rep],　　{m,}:[m, infi),　　{,n}:[0,n],　　{m,n}:[m,n],　　

　　　　? (nogreedy option)

 　　2, Begin and End:

　　 　　^: beginning,　　 $: ending

　　3, Making own character class:

　　　　[abc]　　,[^abc]: ^ rep non
　　4, Character classes:

　　 　　d,D,s,S,w,W
　　5: dot (or wildcard) character:

　　　　. , 　　.*,　　(.*) ? : rep nongreedy fashion

II, Usefull regex arguments

　　1, re.DOTALL : match all characters, including the newline character.

　　2, re.I (re.IGNORECASE): ignore uppercase 

　　3, re.VERBOSE : spread the regex over multiple lines with comments.

　　4, | : we could use pipe character to cobine all three above arguments.

III, generate regex procedure:

　　1, regex = re.compile(r"")

　　2.1.1, regex.search("")

　　2.1.2, regex.search("").group(), (or regex.search("").group(No.)),　　greedy defalut

　　2.2, regex.findall("")

　　2.3 regex.sub("")

　　3 , re.compile(r'''( )''', re.VERBOSE) : to manage more complex regrexes.