Python regular expression,

Python regular expression,
Python Regular Expression learning Summary: 1. First, we recommend the Learning Website:

Cainiao learning: http://www.runoob.com/python/python-reg-expressions.html

MOOC: http://www.imooc.com/learn/550

Self-improvement school: http://code.ziqiangxuetang.com/regexp/regexp-tutorial.html

2. recommended books: Basic python tutorials and core python programming (with python basics) 3. My personal summary:

The most important thing about python is source code learning!

Python has added the re module since version 1.5. It provides the Perl-style regular expression mode. The re module enables the Python language to have all the regular expression functions.

Regular Expression match mainly includes: single character match, boundary match, Character Set match, restriction and negation, group match and extended notation. The following is a summary:

1. Single Character matching

\ Cx	Match the control characters specified by x. For example, \ cM matches a Control-M or carriage return character. The value of x must be either a A-Z or a-z. Otherwise, c is treated as an original 'C' character.
\ D	Match a numeric character. It is equivalent to [0-9].
\ D	Match a non-numeric character. It is equivalent to [^ 0-9].
\ F	Match a form feed. It is equivalent to \ x0c and \ cL.
\ N	Match A linefeed. It is equivalent to \ x0a and \ cJ.
\ R	Match a carriage return. It is equivalent to \ x0d and \ cM.
\ S	Matches any blank characters, including spaces, tabs, and page breaks. It is equivalent to [\ f \ n \ r \ t \ v].
\ S	Match any non-blank characters. It is equivalent to [^ \ f \ n \ r \ t \ v].
\ T	Match a tab. It is equivalent to \ x09 and \ cI.
\ V	Match a vertical tab. It is equivalent to \ x0b and \ cK.
\ W	Match any word characters that contain underscores. It is equivalent to '[A-Za-z0-9 _]'.
\ W	Match any non-word characters. It is equivalent to '[^ A-Za-z0-9 _]'.
\ Xn	Match n, where n is the hexadecimal escape value. The hexadecimal escape value must be determined by the length of two numbers. For example, '\ x41' matches "". '\ X041' is equivalent to '\ x04' & "1 ". The regular expression can be ASCII encoded.
\ Num	Matches num, where num is a positive integer. References to the obtained matching. For example, '(.) \ 1' matches two consecutive identical characters.
\ N	Identifies an octal escape value or a backward reference. If at least n subexpressions are obtained before \ n, n is backward referenced. Otherwise, if n is an octal digit (0-7), n is an octal escape value.
\ Nm	Identifies an octal escape value or a backward reference. If at least one child expression is obtained before \ nm, the nm is backward referenced. If at least n records are obtained before \ nm, n is a backward reference followed by text m. If none of the preceding conditions are met, if n and m are Octal numbers (0-7), \ nm matches the octal escape value nm.
\ Nml	If n is an octal number (0-3) and m and l are Octal numbers (0-7), the octal escape value nml is matched.
\ Un	Match n, where n is a Unicode character represented by four hexadecimal numbers. For example, \ u00A9 matches the copyright symbol (?).

2. boundary matching

\ B	Match A Word boundary, that is, the position between a word and a space. For example, 'er \ B 'can match 'er' in "never", but cannot match 'er 'in "verb '.
\ B	Match non-word boundary. 'Er \ B 'can match 'er' in "verb", but cannot match 'er 'in "never '.

^ | \	Matches the start position of the input string. If the Multiline attribute of the RegExp object is set, ^ matches the position after '\ n' or' \ R.
$ | \ Z	Matches the end position of the input string. If the Multiline attribute of the RegExp object is set, $ also matches the position before '\ n' or' \ R.

3. Character Set matching

[Xyz]	Character Set combination. Match any character in it. For example, '[abc]' can match 'A' in "plain '.
[^ Xyz]	Negative value character set combination. Match any character not included. For example, '[^ abc]' can match 'p' in "plain '.

4. Restriction and Negation

[A-z]	Character range. Matches any character in the specified range. For example, '[a-z]' can match any lowercase letter in the range of 'A' to 'Z.
[^ A-z]	Negative character range. Matches any character that is not within the specified range. For example, '[^ a-z]' can match any character that is not in the range of 'A' to 'Z.

5. group matching

\ D + (\. \ d *)?	A string that represents a simple floating point number.
([\ W] +) \ w + \ 1	Matches html or xml tags. <span> python <span>

6. Extended notation

(? : Pattern)	Matches pattern but does not get the matching result. That is to say, this is a non-get match and is not stored for future use. For example, 'industr (? : Y | ies) is a simpler expression than 'industry | industries.
(? = Pattern)	Forward pre-query: matches the search string at the beginning of any string that matches the pattern.
(?! Pattern)	Negative pre-query: matches the search string at the beginning of any string that does not match pattern.
X | y	Match x or y. For example, 'z | food' can match "z" or "food ". '(Z | f) ood' matches "zood" or "food ".

The most important thing is naming combinations and non-Greedy use:

(* | + |? | {})? It is used to match the non-Greedy version of the above frequently repeated symbols.

(? P <name>...) # name is a valid identifier used to name a capture group.

In addition:

　　　　It is best to use the original character pattern = r'pattern' to define pattern in python'

Attached python doc-re module:Https://docs.python.org/3/library/re.html