A positive lookbehind assertion in Python’s re module is a zero-width assertion that checks if the pattern that precedes it is present, without including that pattern in the overall match. It’s the opposite of a lookahead. It is written as (?<=…). The key constraint for lookbehind assertions in Python is that the pattern inside the…

A positive lookahead assertion in Python’s re module is a zero-width assertion that checks if the pattern that follows it is present, without including that pattern in the overall match. It is written as (?=…). The key is that it’s a “lookahead”—the regex engine looks ahead in the string to see if the pattern inside…

To create a non-capturing group in Python’s re module, you use the syntax (?:…). This groups a part of a regular expression together without creating a backreference for that group. A capturing group (…) saves the matched text. You can then access this captured text using methods like group(1), group(2), etc. A non-capturing group (?:…)…

1. \A and \Z – String Anchors \A – Matches ONLY at the beginning of the string \Z – Matches ONLY at the end of the string Example 1: \A – Start of string python import re text = “Hello World\nHello Python” pattern = r”\AHello” # Match “Hello” only at the VERY beginning matches =…

Curly Braces {} in Python Regex Curly braces {} are used to specify exact quantity of the preceding character or group. They define how many times something should appear. Basic Syntax: Example 1: Exact Number of Digits python import re text = “Zip codes: 12345, 9876, 123, 123456, 90210″ # Match exactly 5 digits pattern = r”\d{5}” # Exactly…

The Question Mark (?) in Python Regex The question mark ? in Python’s regular expressions has two main uses: 1. Making a Character or Group Optional (0 or 1 occurrence) This is the most common use – it makes the preceding character or group optional. Examples: Example 1: Optional ‘s’ for plural words python import re pattern…

The Dot (.) Metacharacter in Simple Terms Think of the dot . as a wildcard that can stand in for any single character. It’s like a placeholder that matches whatever character is in that position. What the Dot Does: Example 1: Finding Words with a Pattern python import re # Let’s find all 3-letter words that end with “at” text…

AttributeError: ‘NoneType’ Error in Python re This error occurs when you try to call match object methods on None instead of an actual match object. It’s one of the most common errors when working with Python’s regex module. Why This Happens: The re.search(), re.match(), and re.fullmatch() functions return: When you try to call methods like .group(), .start(), or .span() on None, you get this error. Example That Causes…

Python re Flags: re.I, re.S, re.X Explained Flags modify how regular expressions work. They’re used as optional parameters in re functions like re.search(), re.findall(), etc. 1. re.I or re.IGNORECASE Purpose: Makes the pattern matching case-insensitive Without re.I (Case-sensitive): python import re text = “Hello WORLD hello World” # Case-sensitive search matches = re.findall(r’hello’, text) print(“Case-sensitive:”, matches) # Output: [‘hello’] # Only finds lowercase…

Python re start(), end(), and span() Methods Explained These methods are used with match objects to get the positional information of where a pattern was found in the original string. They work on the result of re.search(), re.match(), or re.finditer(). Methods Overview: Example 1: Basic Position Tracking python import re text = “The quick brown fox jumps over the lazy…