常用函数：
match 从头匹配
search 匹配包含
findall 匹配所有，返回列表
split 匹配到的字符作为列表分隔符
sub 匹配字符并替换
import re
# match
res = re.match("I", "ILoveYou1314")
print(res) # <_sre.SRE_Match object; span=(0, 1), match='I'>
print(res.group()) # I
# []匹配区间
res = re.match("[a-zA-Z]*", "ILoveYou1314")
print(res.group()) # ILoveYou
# ^开头，$结束
res = re.search("^I*", "ILoveYou1314")
print(res.group()) # I
# .任意字符，*零次或多次
res = re.search(".*u", "ILoveYou1314")
print(res.group()) # ILoveYou
# +匹配1次或多次
res = re.search("\d+", "ILoveYou1314")
print(res.group()) # 1314
# {n, m}匹配n到m
res = re.findall("\d{1,3}", "I1Love234You1314")
print(res) # ['1', '234', '131', '4']
# ?匹配0次或1次
res = re.findall("ov?", "I1Love234You1314")
print(res) # ['ov', 'o']
# | 或
res = re.findall("abc|ABC", "abcefdAbcfdfABC")
print(res) # ['abc', 'ABC']
# 命名
res = re.search("(?P<id>\d{3})(?P<name>\w{4})", "123abcefdAbcfdfABC")
print(res.groupdict()) # {'id': '123', 'name': 'abce'}
# 拆分
res = re.split("\d+", "123abcefdAbc123fdfABC")
print(res) # ['', 'abcefdAbc', 'fdfABC']
# 替换
res = re.sub("\d+", "|", "123abcefdAbc123fdfABC")
print(res) # |abcefdAbc|fdfABC
# 匹配斜杠
res = re.search(r"\\",r"123ab\cefdAbc123fdfABC")
print(res.group()) # \
# flags
# re.I 忽略大小写 re.M 忽略多行 re.S 匹配任意字符
res = re.findall("abc",r"123abccefdAbc123fdfABC",flags=re.I)
print(res) # ['abc', 'Abc', 'ABC']
# help(re)
"""
re - Support for regular expressions (RE).
The special characters are:
"." Matches any character except a newline.
"^" Matches the start of the string.
"$" Matches the end of the string or just before the newline at
the end of the string.
"*" Matches 0 or more (greedy) repetitions of the preceding RE.
Greedy means that it will match as many repetitions as possible.
"+" Matches 1 or more (greedy) repetitions of the preceding RE.
"?" Matches 0 or 1 (greedy) of the preceding RE.
*?,+?,?? Non-greedy versions of the previous three special characters.
{m,n} Matches from m to n repetitions of the preceding RE.
{m,n}? Non-greedy version of the above.
"\\" Either escapes special characters or signals a special sequence.
[] Indicates a set of characters.
A "^" as the first character indicates a complementing set.
"|" A|B, creates an RE that will match either A or B.
(...) Matches the RE inside the parentheses.
The contents can be retrieved or matched later in the string.
(?aiLmsux) Set the A, I, L, M, S, U, or X flag for the RE (see below).
(?:...) Non-grouping version of regular parentheses.
(?P<name>...) The substring matched by the group is accessible by name.
(?P=name) Matches the text matched earlier by the group named name.
(?#...) A comment; ignored.
(?=...) Matches if ... matches next, but doesn't consume the string.
(?!...) Matches if ... doesn't match next.
(?<=...) Matches if preceded by ... (must be fixed length).
(?<!...) Matches if not preceded by ... (must be fixed length).
(?(id/name)yes|no) Matches yes pattern if the group with id/name matched,
the (optional) no pattern otherwise.
The special sequences consist of "\\" and a character from the list
below. If the ordinary character is not on the list, then the
resulting RE will match the second character.
\number Matches the contents of the group of the same number.
\A Matches only at the start of the string.
\Z Matches only at the end of the string.
\b Matches the empty string, but only at the start or end of a word.
\B Matches the empty string, but not at the start or end of a word.
\d Matches any decimal digit; equivalent to the set [0-9] in
bytes patterns or string patterns with the ASCII flag.
In string patterns without the ASCII flag, it will match the whole
range of Unicode digits.
\D Matches any non-digit character; equivalent to [^\d].
\s Matches any whitespace character; equivalent to [ \t\n\r\f\v] in
bytes patterns or string patterns with the ASCII flag.
In string patterns without the ASCII flag, it will match the whole
range of Unicode whitespace characters.
\S Matches any non-whitespace character; equivalent to [^\s].
\w Matches any alphanumeric character; equivalent to [a-zA-Z0-9_]
in bytes patterns or string patterns with the ASCII flag.
In string patterns without the ASCII flag, it will match the
range of Unicode alphanumeric characters (letters plus digits
plus underscore).
With LOCALE, it will match the set [0-9_] plus characters defined
as letters for the current locale.
\W Matches the complement of \w.
\\ Matches a literal backslash.
This module exports the following functions:
match Match a regular expression pattern to the beginning of a string.
fullmatch Match a regular expression pattern to all of a string.
search Search a string for the presence of a pattern.
sub Substitute occurrences of a pattern found in a string.
subn Same as sub, but also return the number of substitutions made.
split Split a string by the occurrences of a pattern.
findall Find all occurrences of a pattern in a string.
finditer Return an iterator yielding a match object for each match.
compile Compile a pattern into a RegexObject.
purge Clear the regular expression cache.
escape Backslash all non-alphanumerics in a string.
FUNCTIONS
compile(pattern, flags=0)
Compile a regular expression pattern, returning a pattern object.
escape(pattern)
Escape all the characters in pattern except ASCII letters, numbers and '_'.
findall(pattern, string, flags=0)
Return a list of all non-overlapping matches in the string.
Empty matches are included in the result.
finditer(pattern, string, flags=0)
Return an iterator over all non-overlapping matches in the
fullmatch(pattern, string, flags=0)
Try to apply the pattern to all of the string, returning
a match object, or None if no match was found.
match(pattern, string, flags=0)
Try to apply the pattern at the start of the string, returning
a match object, or None if no match was found.
purge()
Clear the regular expression caches
search(pattern, string, flags=0)
Scan through string looking for a match to the pattern, returning
a match object, or None if no match was found.
split(pattern, string, maxsplit=0, flags=0)
Split the source string by the occurrences of the pattern,
returning a list containing the resulting substrings.
sub(pattern, repl, string, count=0, flags=0)
Return the string obtained by replacing the leftmost
non-overlapping occurrences of the pattern in string by the
replacement repl.
subn(pattern, repl, string, count=0, flags=0)
Return a 2-tuple containing (new_string, number).
template(pattern, flags=0)
Compile a template pattern, returning a pattern object
"""