Week 7: Regualr Expressions

Week 7: Practice Code	GitHub

Regular Expressions

A RegEx, or Regular Expression, is a sequence of characters that forms a search pattern. — W3School

RegEx can be used to check if a string contains the specified search pattern.

Python has a built-in packaged called re, which can be used to word with Regular Expressions.

Import the re module:

import re

Metacharacters are characters with a special meaning:

Character	Description	Example
[]	A set of characters	“[a-m]”
\	Signals a special sequence (can also be used to escape special characters)	“\d”
.	Any character (except newline character)	“he..o”
.	Starts with	“^hello”
$	Ends with	“planet$”
*	Zero or more occurrences	“he.*o”
+	One or more occurrences	“he.+o”
?	Zero or one occurrences	“he.?o”
{}	Exactly the specified number of occurrences	“he.{2}.o”
{m,n}	m-n range of repetitions	“he.{2,4}.o”
\|	Either or	“falls\|stays”
()	Capture and group

You can add flags to the pattern when using regular expressions.

A special sequence is a \ followed by one of the characters in the list below, and has a special mean:

A set is a set of characters inside a pair of square brackets [] with a special meaning: