Regular expression is a logical formula for string operation , It is to use some specific characters defined in advance 、 And the combination of these specific characters , Form a “ Rule string ”, To filter out the content that meets this rule .

It can be simply understood as ： A powerful search tool , A regular expression is a conditional expression for what you want to search .

1. re.findall（） function

effect ： Traversing the entire string , You can get all the matching strings , Return a list .

General usage ：

re.findall(r' Regular expressions ',' Text to match ')

2. Practice contact regularity from childhood

1. Match words from strings to:

import re
text = "0537-146987425,0537-299656897,The moment you think about giving up,think of the reason why you held on so long. Total umbrella for someone else if he, you’re just not for him in the rain.Never put your happiness in someone else’s hands.Sometimes you have to give up on someone in order to respect yourself. aaaa bbbbcc d dddddd"
print(re.findall(r'to',text))

• Output ：

['to', 'to']

2. Match in text China and Israel g All words at the beginning ：

print(re.findall(r'\bg\w*?\b',text))

• Output ：

['giving', 'give']

3. Find letters with length 4 's words ：

print(re.findall(r'\b\w{4}\b',text))

• Output ：

['0537', '0537', 'held', 'long', 'else', 'just', 'rain', 'your', 'else', 'have', 'give', 'aaaa']

4. Find out xxxx-xxxxxxxxx Formatted data ：

print(re.findall(r'\d{4}-\d{8}',text))

• Output ：

['0537-14698742', '0537-29965689']

3. Regular expression metacharacters

Metacharacters Functional specifications ^ Matches the beginning of the string $ Matches the end of the string . Matches any character other than a newline character \d Match the Numbers \b Match the beginning or end of the word \w Match any letter 、 Numbers and underscores \s Matches any whitespace characters , Including Spaces 、 tabs 、 Page identifier \B And \b contrary , Match non word boundaries \W And \w contrary \S And \s contrary {m,n}{} The preceding character or sub pattern repeats at least m Time , at most n Time