Python – Regular Expressions (RegEx)
1. What is Regular Expression?
A Regular Expression (RegEx) is a pattern used to find, match, or replace text.
In simple words:
👉 RegEx helps you search text smartly
👉 It is used to check patterns
👉 Very useful for emails, phone numbers, passwords
2. Why Use RegEx?
We use RegEx to:
✔ Find text
✔ Validate input
✔ Replace text
✔ Extract data
3. RegEx Module in Python
Python has a built-in module called re.
Import RegEx Module
4. Simple RegEx Example
Example: Find a Word
👉 Finds the word Python.
5. Common RegEx Functions
| Function | Use |
|---|---|
re.search() |
Find first match |
re.findall() |
Find all matches |
re.match() |
Match from start |
re.sub() |
Replace text |
6. re.search() Example
Example
7. re.findall() Example
Example
Output:
8. re.match() Example
Matches only at beginning.
Example
9. re.sub() (Replace Text)
Example
Output:
10. Common RegEx Patterns
| Pattern | Meaning |
|---|---|
\d |
Any digit |
\w |
Word character |
\s |
Space |
. |
Any character |
^ |
Start of text |
$ |
End of text |
* |
Zero or more |
+ |
One or more |
11. Find Numbers in Text
Example
12. Validate Email (Simple)
Example
13. Check Phone Number
Example
14. Split Text Using RegEx
Example
15. Case-Insensitive Search
Example
16. Common Beginner Mistakes
❌ Forgetting to import re
❌ Using wrong pattern
❌ Forgetting raw string (r"")
❌ Confusing search() and match()
17. Simple Practice Examples
Example 1: Find All Digits
Example 2: Replace Spaces
Example 3: Check Username
18. Summary (Python Regular Expressions)
✔ RegEx is for pattern matching
✔ Uses re module
✔ Very useful for validation
✔ Powerful but needs practice
✔ Used in real-world applications
📘 Perfect for Beginner & Intermediate eBook
This chapter is ideal for:
-
Python learners
-
Input validation
-
Text processing
-
Interview preparation
If you want next, I can write:
-
Advanced RegEx Patterns
-
Password Validation Using RegEx
-
Real-world RegEx Projects
-
Python Interview Questions
Just tell me 😊
