diff --git a/contrib/advanced-python/regular_expressions.md b/contrib/advanced-python/regular_expressions.md index 65ff2c2..a867981 100644 --- a/contrib/advanced-python/regular_expressions.md +++ b/contrib/advanced-python/regular_expressions.md @@ -1,6 +1,7 @@ ## Regular Expressions in Python Regular expressions (regex) are a powerful tool for pattern matching and text manipulation. Python's re module provides comprehensive support for regular expressions, enabling efficient text processing and validation. +Regular expressions (regex) are a versitile tool for matching patterns in strings. In Python, the `re` module provides support for working with regular expressions. ## 1. Introduction to Regular Expressions A regular expression is a sequence of characters defining a search pattern. Common use cases include validating input, searching within text, and extracting @@ -20,7 +21,81 @@ Metacharacters: Special characters like ., *, ?, +, ^, $, [ ], and | used to bui * ?: 0 or 1 repetition. * []: Any one character inside brackets (e.g., [a-z]). * |: Either the pattern before or after. - +* \ : Used to drop the special meaning of character following it +* {} : Indicate the number of occurrences of a preceding regex to match. +* () : Enclose a group of Regex + +Examples: +```bash +1. `.` +import re +pattern = r'c.t' +text = 'cat cot cut cit' +matches = re.findall(pattern, text) +print(matches) # Output: ['cat', 'cot', 'cut', 'cit'] + +2. `^` +pattern = r'^Hello' +text = 'Hello, world!' +match = re.search(pattern, text) +print(match.group() if match else 'No match') # Output: 'Hello' + +3. `$` +pattern = r'world!$' +text = 'Hello, world!' +match = re.search(pattern, text) +print(match.group() if match else 'No match') # Output: 'world!' + +4. `*` +pattern = r'ab*' +text = 'a ab abb abbb' +matches = re.findall(pattern, text) +print(matches) # Output: ['a', 'ab', 'abb', 'abbb'] + +5. `+` +pattern = r'ab+' +text = 'a ab abb abbb' +matches = re.findall(pattern, text) +print(matches) # Output: ['ab', 'abb', 'abbb'] + +6. `?` +pattern = r'ab?' +text = 'a ab abb abbb' +matches = re.findall(pattern, text) +print(matches) # Output: ['a', 'ab', 'ab', 'ab'] + +7. `[]` +pattern = r'[aeiou]' +text = 'hello world' +matches = re.findall(pattern, text) +print(matches) # Output: ['e', 'o', 'o'] + +8. `|` +pattern = r'cat|dog' +text = 'I have a cat and a dog.' +matches = re.findall(pattern, text) +print(matches) # Output: ['cat', 'dog'] + +9. `\`` +pattern = r'\$100' +text = 'The price is $100.' +match = re.search(pattern, text) +print(match.group() if match else 'No match') # Output: '$100' + +10. `{}` +pattern = r'\d{3}' +text = 'My number is 123456' +matches = re.findall(pattern, text) +print(matches) # Output: ['123', '456'] + +11. `()` +pattern = r'(cat|dog)' +text = 'I have a cat and a dog.' +matches = re.findall(pattern, text) +print(matches) # Output: ['cat', 'dog'] + +``` + ## 3. Using the re Module **Key functions in the re module:** @@ -29,7 +104,8 @@ Metacharacters: Special characters like ., *, ?, +, ^, $, [ ], and | used to bui * re.search(): Searches for a match anywhere in the string. * re.findall(): Returns a list of all matches. * re.sub(): Replaces matches with a specified string. - +* re.split(): Returns a list where the string has been split at each match. +* re.escape(): Escapes special character Examples: ```bash import re @@ -45,6 +121,12 @@ print(re.findall(r'\d+', 'abc123def456')) # Output: ['123', '456'] # Substitute matches print(re.sub(r'\d+', '#', 'abc123def456')) # Output: abc#def# + +#Return a list where it get matched +print(re.split("\s", txt)) #['The', 'Donkey', 'in', 'the','Town'] + +# Escape special character +print(re.escape("We are good to go")) #We\ are\ good\ to\ go ``` ## 4. Compiling Regular Expressions @@ -58,6 +140,7 @@ pattern = re.compile(r'\d+') print(pattern.match('123abc').group()) # Output: 123 print(pattern.search('abc123').group()) # Output: 123 print(pattern.findall('abc123def456')) # Output: ['123', '456'] + ``` ## 5. Groups and Capturing @@ -78,19 +161,38 @@ if match: ## 6. Special Sequences Special sequences are shortcuts for common patterns: +* \A:Returns a match if the specified characters are at the beginning of the string. +* \b:Returns a match where the specified characters are at the beginning or at the end of a word. +* \B:Returns a match where the specified characters are present, but NOT at the beginning (or at the end) of a word. * \d: Any digit. * \D: Any non-digit. * \w: Any alphanumeric character. * \W: Any non-alphanumeric character. * \s: Any whitespace character. * \S: Any non-whitespace character. +* \Z:Returns a match if the specified characters are at the end of the string. + Example: ```bash import re print(re.search(r'\w+@\w+\.\w+', 'Contact: support@example.com').group()) # Output: support@example.com ``` +## 7.Sets +A set is a set of characters inside a pair of square brackets [] with a special meaning: + +* [arn] : Returns a match where one of the specified characters (a, r, or n) is present. +* [a-n] : Returns a match for any lower case character, alphabetically between a and n. +* [^arn] : Returns a match for any character EXCEPT a, r, and n. +* [0123] : Returns a match where any of the specified digits (0, 1, 2, or 3) are present. +* [0-9] : Returns a match for any digit between 0 and 9. +* [0-5][0-9] : Returns a match for any two-digit numbers from 00 and 59. +* [a-zA-Z] : Returns a match for any character alphabetically between a and z, lower case OR upper case. +* [+] : In sets, +, *, ., |, (), $,{} has no special meaning, so [+] means: return a match for any + character in the string. ## Summary -Regular expressions are a versatile tool for text processing in Python. The re module offers powerful functions and metacharacters for pattern matching, -searching, and manipulation, making it an essential skill for handling complex text processing tasks. +Regular expressions (regex) are a powerful tool for text processing in Python, offering a flexible way to match, search, and manipulate text patterns. The re module provides a comprehensive set of functions and metacharacters to tackle complex text processing tasks. +With regex, you can: +1.Match patterns: Use metacharacters like ., *, ?, and {} to match specific patterns in text. +2.Search text: Employ functions like re.search() and re.match() to find occurrences of patterns in text. +3.Manipulate text: Utilize functions like re.sub() to replace patterns with new text.