{} () [] and re.match re.search in regular expressions
1. Regular expressions
() is to extract matching strings. There are several () in the expression, there are several corresponding matching strings.
(\s*) A string representing consecutive spaces.
(\d*) represents a continuous number, similar to [0-9]+
[] is the character range that defines the match. For example,[a-zA-Z0-9] indicates that the characters in the corresponding position should match English characters and numbers. [\s*] indicates a space or an *.
{} is generally used to indicate the length of the match, such as\s{3} for matching three spaces,\s[1,3] for matching one to three spaces.
(0-9)Matches '0-9' itself. [0-9]* Matching digits (note *, can be empty)[0-9]+ matching digits (note +, can not be empty){1-9} is written incorrectly.
[0-9]{0,9} represents a numeric string of length 0 to 9
Examples of []* and []+:
[]* can return control, that is, can not find the value, but [0-9]+ can not be empty, if empty return error
>>> c='GET /diviner? pin=1123066825_m&p='
>>> r=re.search('p=([0-9]+)',c)
>>> print r.group(1)
Traceback (most recent call last):
File "", line 1, in
AttributeError: 'NoneType' object has no attribute 'group'
>>> print r
None
>>> r=re.search('p=([0-9]*)',c)
>>> print r.group(1)
---Return empty here
2.re mathc search Description
match () function only checks if RE matches at the beginning of string,
search() scans the entire string for a match;
>>> a='123aaabcabcabc'
>>> import re
>>> re.search('abc',a)
>>> re.mathc('abc',a)
Traceback (most recent call last):
File "", line 1, in
AttributeError: 'module' object has no attribute 'mathc'
>>> re.match('abc',a)
>>> b=re.match('abc',a)
>>> print b
None
>>> b=re.match('1',a)
>>> pint b
File "", line 1
pint b
^
SyntaxError: invalid syntax
>>> print b
() in the role of group groups---mainly plays the role of grouping
>>> c='GET /diviner? pin=1123066825_m&p=61234'
>>> r=re.search('p=((\d*))',c)
>>> print c.group(0)
Traceback (most recent call last):
File "", line 1, in
AttributeError: 'str' object has no attribute 'group'
>>> print r.group(0)
p=61234
>>> r=re.search('p=((\d*))',c)
>>> r=re.search('p=([0-9]*)',c)
>>> r=re.search('p=[0-9]*',c)
>>> print r.group
>>> print r.group(0)
p=61234
>>> print r.group (1)---No parenthesis No grouping
Traceback (most recent call last):
File "", line 1, in
IndexError: no such group
>>> r=re.search('p=([0-9]*)',c)
>>> print r.group(1)
61234
