Python Regular Expressions

First, the common method

FindAll: Matches all conforming content and returns a list containing the results

Search: Matches and extracts the first conforming content, returning a regular Expression object (object)

Sub: Replaces the content that matches the rule, returning the replaced value.

S: Indicates multi-line matching

Note: The difference between findall and search:

FindAll will iterate through the contents of the entire loading range, and return each match to the content;

Search once matched to the specified content will no longer match, return the results, searching the end.

Second, commonly used symbols:

. Number: Matches any character, except for line break \ n

>>>ImportRe>>> a='xy123'>>> B=re.findall ('x.', a)>>>Print(b) ['XY']>>> B=re.findall ('x..', a)>>>Print(b) ['xy1']

* Number: Match the previous character 0 or unlimited times

>>> a='xyxy123'>>> b=re.findall ('x*'  , a)print  (b) ['x''x ' "' "' "' "' "]

？ Number: Match the previous character 0 or 1 times

>>> a='xyxy123'>>> b=re.findall ('x.? ' , a) Print b['x ' ' x ' "' "' "' "]

Note: ' Indicates a match 0 times

+ No: Matches the previous character at least once (one or more times)

>>> a='xyxy123'>>> b=re.findall ('x+'  , a)print  b['x'x']

. * Number: Greedy algorithm

Import re>>> secret_code='hadkfalifexxixxfasdjifja134xxlovexx23345sdfxxyouxx8dfse '>>> b=re.findall ('xx.*xx', secret_code)print b['xxixxfasdjifja134xxlovexx23345sdfxxyouxx']

. * No.: Non-greedy algorithm

Import re>>>secret_code='hadkfalifexxixxfasdjifja134xxlovexx23345sdfxxyouxx8dfse '>>> b=re.findall ('xx.*?xx', secret_code)print b['xxixx'xxlovexx ' Xxyouxx ']

(): The data in parentheses is returned as a result

Import re>>>secret_code='hadkfalifexxixxfasdjifja134xxlovexx23345sdfxxyouxx8dfse '>>> b=re.findall ('xx (. *?) xx', secret_code)print  b['I'  Love "You")

#匹配纯数据方法举例 (\d+)

>>> a='asdfefrg137143fdfhxs4321ddfdvsdf543dd'>>> b=re.findall ('  (\d+)', a)print  b['137143'  '4321'543']

Actual combat-making a text crawler

destination URL:http://www.imtech.res.in/raghava/sarpred/data/Manesh-215/PSSM/

Target content: Extract the specified file contents

Implementation principle:

1. Save the Web page source code

2.python read file load source code

3. Regular expression Extraction

4. Write # Coding=utf-8

ImportUrllibImportRedefgethtml (URL): page=urllib.urlopen (URL) HTML=Page.read ()returnHTMLdefgetreq (HTML):
REG1=r'href= "(. *?\.mtx)" >'REG2=r'href= "(. *?) \.MTX ">'MTX=re.compile (REG1) title=re.compile (REG2) mtxlist=Re.findall (mtx,html) titlelist=Re.findall (title,html) FP=open ('D://manesh-215.txt','W') I=0 forRequrlinchMtxlist:strurl='http://www.imtech.res.in/raghava/sarpred/data/Manesh-215/PSSM/'+Requrl mtxpage=Urllib.urlopen (strurl) mtxhtml=Mtxpage.readlines () St=">query |"+titlelist[i]+" | Length="+Mtxhtml[0] Fp.write (ST) Fp.write (mtxhtml[1]) I=i+1fp.close ()

Python Regular Expressions