From b2ef489f44925b489c9634dfd9f727153283b436 Mon Sep 17 00:00:00 2001 From: Damini2004 Date: Wed, 26 Jun 2024 14:31:54 +0530 Subject: [PATCH] Commit -2 --- .../advanced-python/regular_expressions.md | 131 ++++++++++++------ 1 file changed, 88 insertions(+), 43 deletions(-) diff --git a/contrib/advanced-python/regular_expressions.md b/contrib/advanced-python/regular_expressions.md index a867981..040a8c7 100644 --- a/contrib/advanced-python/regular_expressions.md +++ b/contrib/advanced-python/regular_expressions.md @@ -1,112 +1,147 @@ ## Regular Expressions in Python -Regular expressions (regex) are a powerful tool for pattern matching and text manipulation. + +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 + +A regular expression is a sequence of characters defining a search pattern. Common use cases include validating input, searching within text, and extracting specific patterns. ## 2. Basic Syntax + Literal Characters: Match exact characters (e.g., abc matches "abc"). -Metacharacters: Special characters like ., *, ?, +, ^, $, [ ], and | used to build patterns. +Metacharacters: Special characters like ., \*, ?, +, ^, $, [ ], and | used to build patterns. **Common Metacharacters:** -* .: Any character except newline. -* ^: Start of the string. -* $: End of the string. -* *: 0 or more repetitions. -* +: 1 or more repetitions. -* ?: 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 +- .: Any character except newline. +- ^: Start of the string. +- $: End of the string. +- \*: 0 or more repetitions. +- +: 1 or more repetitions. +- ?: 0 or 1 repetition. +- []: Any one character inside brackets (e.g., [a-z]). +- |: Either the pattern before or after. +- \ : Used to drop the special meaning of character following it +- {} : Indicate the number of occurrences of a preceding regex to match. +- () : Enclose a group of Regex Examples: -```bash + 1. `.` + +```bash import re pattern = r'c.t' text = 'cat cot cut cit' matches = re.findall(pattern, text) print(matches) # Output: ['cat', 'cot', 'cut', 'cit'] +``` 2. `^` + +```bash pattern = r'^Hello' text = 'Hello, world!' match = re.search(pattern, text) print(match.group() if match else 'No match') # Output: 'Hello' +``` 3. `$` + +```bash pattern = r'world!$' text = 'Hello, world!' match = re.search(pattern, text) print(match.group() if match else 'No match') # Output: 'world!' +``` 4. `*` + +```bash pattern = r'ab*' text = 'a ab abb abbb' matches = re.findall(pattern, text) print(matches) # Output: ['a', 'ab', 'abb', 'abbb'] +``` 5. `+` + +```bash pattern = r'ab+' text = 'a ab abb abbb' matches = re.findall(pattern, text) print(matches) # Output: ['ab', 'abb', 'abbb'] +``` 6. `?` + +```bash pattern = r'ab?' text = 'a ab abb abbb' matches = re.findall(pattern, text) print(matches) # Output: ['a', 'ab', 'ab', 'ab'] +``` 7. `[]` + +```bash pattern = r'[aeiou]' text = 'hello world' matches = re.findall(pattern, text) print(matches) # Output: ['e', 'o', 'o'] +``` 8. `|` + +```bash pattern = r'cat|dog' text = 'I have a cat and a dog.' matches = re.findall(pattern, text) print(matches) # Output: ['cat', 'dog'] +``` 9. `\`` + +```bash pattern = r'\$100' text = 'The price is $100.' match = re.search(pattern, text) print(match.group() if match else 'No match') # Output: '$100' +``` 10. `{}` + +```bash pattern = r'\d{3}' text = 'My number is 123456' matches = re.findall(pattern, text) print(matches) # Output: ['123', '456'] +``` 11. `()` + +```bash 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:** -* re.match(): Checks for a match at the beginning of the string. -* 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: +- re.match(): Checks for a match at the beginning of the string. +- 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 @@ -122,7 +157,7 @@ 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 +#Return a list where it get matched print(re.split("\s", txt)) #['The', 'Donkey', 'in', 'the','Town'] # Escape special character @@ -130,9 +165,11 @@ print(re.escape("We are good to go")) #We\ are\ good\ to\ go ``` ## 4. Compiling Regular Expressions + Compiling regular expressions improves performance for repeated use. Example: + ```bash import re @@ -144,9 +181,11 @@ print(pattern.findall('abc123def456')) # Output: ['123', '456'] ``` ## 5. Groups and Capturing + Parentheses () group and capture parts of the match. Example: + ```bash import re @@ -159,40 +198,46 @@ 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. +- \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. +- [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 +- [+] means: return a match for any + character in the string. ## Summary + 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. +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.