REGEX, short for Regular Expression, is a powerful tool used for pattern matching and manipulation of strings. It provides a concise and flexible syntax for describing text patterns, allowing you to search, match, and manipulate text based on specific criteria.
Match the exact characters specified in the pattern.
Example: The regex
applewould match the string "apple" in a text.
These are special characters with a specific meaning.
-
.: any character except a newline. -
*: Matches 0 or more occurrences of the preceding character or group. -
+: Matches 1 or more occurrences of the preceding character or group. -
?: Matches 0 or 1 occurrence of the preceding character or group. -
^: matches the beginning of the string. -
$: matches the end of the string or just before the newline at the end of the string. -
\: Escapes a meta-character, treating it as a literal character. -
{m}: m repetitions -
{m,n}: m-n repetitions -
A|B: either A or B -
(...): a group -
(?:...): non-capturing version -
[]: set of Characters -
[^]: Complementing of Set -
\d: Decimal digit -
\D: not a decimal digit -
\s: whitespace character -
\S: not a whitespace character -
\w: word character as well as numbers and the underscore -
\W: not a word character
import re
# Example 1: Matching a specific word
pattern = re.compile(r'apple')
result = pattern.match('apple pie')
print(result.group()) # Output: apple
# Example 2: Matching any digit
pattern = re.compile(r'\d+')
result = pattern.findall('There are 25 apples and 30 bananas.')
print(result) # Output: ['25', '30']
# Example 3: Matching an email address
pattern = re.compile(r'\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b')
text = 'Contact [email protected] for assistance.'
result = pattern.search(text)
print(result.group()) # Output: [email protected]In these examples:
re.compile()is used to create a regex pattern.match()is used to find a match at the beginning of a string.findall()is used to find all occurrences of the pattern in a string.search()is used to search for the pattern anywhere in the string.