Python中的正则表达式 – 第 2 组（搜索、匹配和查找全部）

Python中的正则表达式与示例|设置 1
模块re为Python中的正则表达式提供支持。以下是该模块中的主要方法。

搜索模式的出现

re.search() ：此方法要么返回 None （如果模式不匹配），要么返回一个 re.MatchObject ，其中包含有关字符串匹配部分的信息。此方法在第一次匹配后停止，因此它最适合测试正则表达式而不是提取数据。

Python3

# 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 ：

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

将模式与文本匹配

re.match() ：此函数尝试将模式匹配到整个字符串。 re.match函数在成功时返回匹配对象，在失败时返回 None。

re.match(pattern, string, flags=0)

pattern : Regular expression to be matched.
string : String where pattern is searched
flags : We can specify different flags 
        using bitwise OR (|). 

Python3

# A Python program to demonstrate working
# of re.match().
import re
    
# a sample function that uses regular expressions
# to find month and day of a date.
def findMonthAndDate(string):
        
    regex = r"([a-zA-Z]+) (\d+)"
    match = re.match(regex, string)
        
    if match == None: 
        print ("Not a valid date")
        return
    
    print ("Given Data: %s" % (match.group()))
    print ("Month: %s" % (match.group(1)))
    print ("Day: %s" % (match.group(2)))
    
        
# Driver Code
findMonthAndDate("Jun 24")
print("")
findMonthAndDate("I was born on June 24")

输出：

Given Data: Jun 24
Month: Jun
Day: 24

Not a valid date

查找所有出现的模式

re.findall() ：返回字符串字符串。该字符串从左到右扫描，并按找到的顺序返回匹配项（来源： Python Docs）。

Python3

# 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)
   
# This example is contributed by Ayush Saluja.

输出 ：

['123456789', '987654321']

正则表达式是一个广阔的话题。这是一个完整的图书馆。正则表达式可以做很多事情。您可以匹配、搜索、替换、提取大量数据。例如，下面的小代码非常强大，它可以从文本中提取电子邮件地址。所以我们可以用easy在Python中制作我们自己的Web Crawlers和scrappers。看下面的正则表达式。

# extract all email addresses and add them into the resulting set
new_emails = set(re.findall(r"[a-z0-9\.\-+_]+@[a-z0-9\.\-+_]+\.[a-z]+", 
                           text, re.I))

我们很快将讨论更多关于正则表达式的方法。