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

先决条件：带有示例的正则表达式 | Python

正则表达式（有时称为 Rational 表达式）是定义搜索模式的字符序列，主要用于与字符串的模式匹配或字符串匹配，即“查找和替换”类操作。正则表达式是一种将模式与字符序列匹配的通用方法。

模块正则表达式 (RE)指定一组与其匹配的字符串（模式）。为了理解 RE 的类比， MetaCharacters是有用的、重要的，并且将用于模块re的功能中。

共有 14 个元字符，将在它们遵循函数时进行讨论：

\   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 or more occurrences
{}  Indicate number of occurrences of a preceding RE 
    to match.
()  Enclose a group of REs

研究（）

re.search()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。

例子：

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

re.findall()

返回字符串字符串。从左到右扫描字符串，并按找到的顺序返回匹配项。

例子：

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) 

输出：

['123456789', '987654321']