How to use Python regular expressions for IP address matching

Regular expression is a powerful character matching tool that can be used to identify and match strings in a certain format. In network programming, IP address is a very important concept, so using regular expressions for IP address matching in Python is a very necessary and practical skill. This article will introduce how to use Python regular expressions for IP address matching.

1. Basic IP address matching expression

The IP address is composed of four numbers, and the value range of each number is 0 to 255. Therefore, a basic IP address matching expression can be written as:

import re

ip_pattern = r'(d{1,3}.){3}d{1,3}'

This expression means to match an IP address consisting of 4 numeric fields, each numeric field consisting of 1 to 3 digits. Numeric fields are separated by periods.

In this expression, we use some basic syntax of regular expressions:

• d: Match numbers
• {n,m}: Match the preceding Pattern n to m times
• .: Match dot number

2. Detailed match of IP address

Although the above expression can match Most IP addresses, but it does not take into account that the IP address number field should range from 0 to 255. To solve this problem, we need to match each numerical field separately and use the regular expression grouping mechanism to limit it.

ip_pattern = r'((25[0-5]|2[0-4]d|[01]?dd?).){3}(25[0-5]|2[0-4]d|[01]?dd?)'

In this expression, we match each number field separately, among which:

• 25[0-5]: Matches numbers between 250 and 255
• 2[0-4]d: Match numbers between 200 and 249
• [01]?dd?: Match numbers between 0 and 199, can be one or two digits Number

This expression uses a grouping mechanism. A parenthesized subexpression is used in the expression of each number field to indicate that this is a grouping. There is also a group at the end of the entire expression, indicating that the entire IP address consists of four numeric fields. In this way, we limit the value range of each numeric field.

3. Matching of IPv6 addresses

In addition to IPv4 addresses, there are also IPv6 addresses, which consist of 8 hexadecimal digits (each number can have 1 to 4 hexadecimal digits) separated by colons. The regular expression of IPv6 address can be written as:

ipv6_pattern = r'[a-fA-F0-9]{1,4}(:[a-fA-F0-9]{1,4}){7}'

This expression means to match an IPv6 address composed of 8 hexadecimal digits, each number can have 1 to 4 hexadecimal digits , numbers are separated by colons.

Summary

Python regular expressions can be used to handle a variety of character matching problems, including IP address matching. When processing IP addresses, you need to consider the value range of the numerical field and use the grouping mechanism to limit it. In addition to IPv4 addresses, there are also IPv6 addresses, which consist of 8 hexadecimal digits and can be matched using similar regular expressions.

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