A detailed description of the Python Express

Regular expressions are used to concisely express a set of strings of expressions, this article is mainly to share with you the Python expression of the knowledge of the detailed, hope to help everyone.

operator	Description	Example
.	Represents any single character
[ ]	Character set, single character value range	[abc]Denotes a or B or C; [A-z] represents a to Z single character
[^ ]	Non-character set, single character exclusion range	[^abc]Represents non-A or non-B or non-C
*	0 or unlimited expansion of the previous character	abc*Saidab、abc、abcc、abccc...
+	1 or unlimited expansion of the previous character	abc+Saidabc、abcc、abccc...
?	0 or 1 expansions of the previous character	abc?Saidab、abc
|	Left or right means any one	abc|defSaidabc或def
{m}	The M-time extension of the previous character	ab{2}Saidabcc
{M,n}	m to n expansions of the previous character (with N)	ab{1,2}Saidabc、abcc
^	Match string start	^abcRepresents ABC and at the beginning of a string
$	Match string End	abc$Represents ABC and at the end of a string
( )	Group tag, internal only using | operator	(abc|def)Saidabc或def
\d	number, equivalent to [0-9]
\w	Word character, equivalent to [a-za-z0-9_]

If you are familiar with the above operator, the following example is not difficult.

1. Enter only the number: ^[0-9]*$

2. Only n digits can be entered: ^\d{n}$

3. You can only enter numbers with at least n digits: ^\d{n,}$

4. Enter only m~n digits: ^\d{m,n}$

5. Only numbers starting with 0 and non 0 can be entered: ^ (0|[ 1-9][0-9]*) $

6. Only positive real numbers with two decimal places can be entered: ^[0-9]+ (. [ 0-9]{2})? $

7. You can only enter positive real numbers with decimal places: ^[0-9]+ (. [ 0-9]{1,3})? $

8. Only non-zero positive integers can be entered: ^+? [1-9] [0-9]*$

"Python3 Regular expression"

function	Description
Re.match ()	Matches a pattern from the starting position of the string, and if the start position match is unsuccessful, match () returns none.
Re.search ()	Scans the entire string and returns the first successful match.
Re.sub ()	A substring used to replace all matching regular expressions in a string, returning the replaced string
Re.findall ()	Search string to return all matching substrings as a list
Re.split ()	Cuts the string according to the regular expression match result, returns the list
Re.finditer ()	Searches for a string that returns the iteration type of a matching result, where each iteration element is a match object

>>> match= Re.findall (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 ') >>> print (match) [' 100081 ', ' 100086 ']>>> match = Re.split (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 ') >>> match["', ' BIT  BIT ', ']>>> ' match = Re.split (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 ', maxsplit=1) >>> match[' , ' BIT  BIT10008676 ']>>>for m in Re.finditer (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 '):       if M:            Print (M.group (0))    100081100086

The difference between Re.match and Re.search

Re.match matches only the beginning of the string, if the string does not begin to conform to the regular expression, the match fails, the function returns none, and Re.search matches the entire string until a match is found.

operator	Description	Example
.	Represents any single character
[ ]	Character set, single character value range	[abc]Denotes a or B or C; [A-z] represents a to Z single character
[^ ]	Non-character set, single character exclusion range	[^abc]Represents non-A or non-B or non-C
*	0 or unlimited expansion of the previous character	abc*Saidab、abc、abcc、abccc...
+	1 or unlimited expansion of the previous character	abc+Saidabc、abcc、abccc...
?	0 or 1 expansions of the previous character	abc?Saidab、abc
|	Left or right means any one	abc|defSaidabc或def
{m}	The M-time extension of the previous character	ab{2}Saidabcc
{M,n}	m to n expansions of the previous character (with N)	ab{1,2}Saidabc、abcc
^	Match string start	^abcRepresents ABC and at the beginning of a string
$	Match string End	abc$Represents ABC and at the end of a string
( )	Group tag, internal only using | operator	(abc|def)Saidabc或def
\d	number, equivalent to [0-9]
\w	Word character, equivalent to [a-za-z0-9_]

If you are familiar with the above operator, the following example is not difficult.

1. Enter only the number: ^[0-9]*$

2. Only n digits can be entered: ^\d{n}$

3. You can only enter numbers with at least n digits: ^\d{n,}$

4. Enter only m~n digits: ^\d{m,n}$

5. Only numbers starting with 0 and non 0 can be entered: ^ (0|[ 1-9][0-9]*) $

6. Only positive real numbers with two decimal places can be entered: ^[0-9]+ (. [ 0-9]{2})? $

7. You can only enter positive real numbers with decimal places: ^[0-9]+ (. [ 0-9]{1,3})? $

8. Only non-zero positive integers can be entered: ^+? [1-9] [0-9]*$

"Python3 Regular expression"

functions	description
re.match () The	matches a pattern from the starting position of the string, and if the start position match is unsuccessful, match () returns none.
re.search ()	scans the entire string and returns the first successful match.
re.sub ()	replaces substrings of all matching regular expressions in a string, returning the replaced string
re.findall ()	search string, return all matching substrings as a list
re.split ()	cut the string to match the regular expression results, return to the list
re.finditer ()	searches for a string that returns the iteration type of a matching result, where each iteration element is a match object

>>> match= Re.findall (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 ') >>> print (match) [' 100081 ', ' 100086 ']>>> match = Re.split (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 ') >>> match["', ' BIT  BIT ', ']>>> ' match = Re.split (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 ', maxsplit=1) >>> match[' , ' BIT  BIT10008676 ']>>>for m in Re.finditer (R ' [1-9]\d{5} ', ' 100081BIT  BIT10008676 '):       if M:            Print (M.group (0))    100081100086

The difference between Re.match and Re.search

Re.match matches only the beginning of the string, if the string does not begin to conform to the regular expression, the match fails, the function returns none, and Re.search matches the entire string until a match is found.