Python Learning notes-Getting started with regular expressions

# This article does not explain the regular knowledge in detail, only as the entry-level regular knowledge directory.

The strong expression of the early heard, the big time to participate in a single exam, the topic is to be used as an HTML parser, the advantages of the regular performance is incisively and vividly. Not much to say, directly on the dry:

1. Meta-characters:

　　　

There are also inverse characters, mostly lowercase letters, such as \d that match non-numeric characters.

2. Repeat (that is, match the variable length string):

Metacharacters can match a single character type, and if you want to match an unknown length or a length-qualified string, you need to add a qualifier behind it.

　　

3. Scope and Grouping:

Sometimes metacharacters do not meet the needs of matching characters, it is necessary to [] to delimit the matching range, for example, to match a word with only a,s,d,f, you can use \b[asdf]\b; there are parentheses in the regular box to represent the grouping, for example, if you want to repeat a certain number of characters, you can use grouping, such as (\d. \d) {1,3} indicates that the duplicate content in the matching parentheses is one to three times. In addition, parentheses can also be used for back-referencing, etc., which are not remembered here.

4.0 Wide Assertion:

0 wide assertions are primarily used to find content before or after certain assertions (the specified content), such as (? =exp) matches the content of the exp preceding (mismatch exp), and(? <=exp) matches the expression that appears after exp, There are also negative 0-wide assertions that are not remembered here.

5. Greed and laziness:

When a regular expression contains a qualifier that can accept duplicates, the usual behavior is to match as many characters as possible , that is, greedy matches, as long as the entire expression can be matched. If the expression a.*b, search Aabab, it will match the entire string Aabab. And the lazy match matches as few strings as possible, just add one after the qualifier? , for example a.*?b will match AaB (first to third character) and AB (fourth to fifth characters).

6. Python's Re module:

　　Python provides a re module that provides all the functionality of the regular. Here are only two methods and a place to note.

　　6.1 Match Method:

　　　　match()The method determines whether the match is successful, returns an object if the match succeeds, Match or returns None .

 1  >>> import   re  2  >>> re.match (r " Span style= "color: #800000;" >^\d{3}\-\d{3,8}$  , "  010-12345    )  3  <_sre. Sre_match object at 0x1026e18b8>4  >>> re.match (r '   

If a group is defined in a regular expression, you can extract the substring from the Match object using a group() method. Notice that group(0) it is always the original string, group(1) group(2) ... Represents the 1th, 2 、...... Substring. All substrings can also be obtained using the groups () method.

　6.2 Split Method:

　　　　The split () method can be used to cut a molecular string, as follows:

1 >>> re.split (R'[\s\,\;] +'b;; c  D')2 ['a'  'b'c'd' ]

　　6.3 About escape characters:

　　　　The Python escape string is also represented by \, so the regular expression reads as a string when it is automatically removed by the compiler, the transfer character's \, the regular use of the error, it is recommended to use the Python R prefix.

Ps:

This article is a summary of the regular expression of learning, most of the knowledge from the Internet. Here are two links that people think are better:

1.http://www.jb51.net/tools/zhengze.html the introduction of regular expressions in detail, personally think to learn more about the regular expression or buy a book is better.

2.http://www.liaoxuefeng.com/wiki/001374738125095c955c1e6d8bb493182103fac9270762a000/ 001386832260566c26442c671fa489ebc6fe85badda25cd000 from the great god of the Liao Xuefeng, in conjunction with Python, just a little bit shorter.

Python Learning notes-Getting started with regular expressions