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Python正则表达式:re.search() VS re.findall()

先决条件: 带示例的正则表达式|Python

一种正则表达式(有时称为Rational表达式)是定义搜索模式的一系列字符, 主要用于与字符串进行模式匹配或字符串匹配(即类似”查找和替换”的操作)。正则表达式是一种将模式与字符序列匹配的通用方法。

模组正则表达式(RE)指定与其匹配的一组字符串(模式)。要了解RE类比, 元字符有用, 重要且将在模块功能中使用re.

一共有14个元字符, 将在功能中进行讨论:

\   Used to drop the special meaning of character
    following it (discussed below)
[]  Represent a character class
^   Matches the beginning
$   Matches the end
.   Matches any character except newline
?   Matches zero or one occurrence.
|   Means OR (Matches with any of the characters
    separated by it.
*   Any number of occurrences (including 0 occurrences)
+   One ore more occurrences
{}  Indicate number of occurrences of a preceding RE 
    to match.
()  Enclose a group of REs

search()

search()方法要么返回None(如果模式不匹配), 要么返回re.MatchObject包含有关字符串匹配部分的信息。此方法在第一个匹配项后停止, 因此它最适合于测试正则表达式, 而不是提取数据。

例子:

# A Python program to demonstrate working of re.match(). 
import re 
    
# Lets use a regular expression to match a date string 
# in the form of Month name followed by day number 
regex = r "([a-zA-Z]+) (\d+)"
    
match = re.search(regex, "I was born on June 24" ) 
    
if match ! = None : 
    
     # We reach here when the expression "([a-zA-Z]+) (\d+)" 
     # matches the date string. 
    
     # This will print [14, 21), since it matches at index 14 
     # and ends at 21.  
     print ( "Match at index % s, % s" % (match.start(), match.end()))
    
     # We us group() method to get all the matches and 
     # captured groups. The groups contain the matched values. 
     # In particular: 
     # match.group(0) always returns the fully matched string 
     # match.group(1) match.group(2), ... return the capture 
     # groups in order from left to right in the input string 
     # match.group() is equivalent to match.group(0) 
    
     # So this will print "June 24" 
     print ( "Full match: % s" % (match.group( 0 )))
    
     # So this will print "June" 
     print ( "Month: % s" % (match.group( 1 )))
    
     # So this will print "24" 
     print ( "Day: % s" % (match.group( 2 )))
    
else : 
     print ( "The regex pattern does not match." )

输出如下:

Match at index 14, 21
Full match: June 24
Month: June
Day: 24

re.findall()

以字符串列表形式返回字符串中所有不重复的模式匹配项。从左到右扫描字符串, 并以找到的顺序返回匹配项。

例子:

# A Python program to demonstrate working of 
# findall() 
import re 
    
# A sample text string where regular expression  
# is searched. 
string = """Hello my Number is 123456789 and 
              my friend's number is 987654321"""
    
# A sample regular expression to find digits. 
regex = '\d+'             
    
match = re.findall(regex, string) 
print (match)

输出如下:

['123456789', '987654321']

首先, 你的面试准备可通过以下方式增强你的数据结构概念:Python DS课程。


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