how to write regex pattern in python?
In Python, you can write and use regular expressions (regex) using the re
module. Here’s a basic overview of how to write and use regex patterns in Python.
Steps to Write a Regex Pattern:
- Import the
re
module: This module provides all the regex-related functionality. - Define a regex pattern: Regex patterns are written as raw strings (prefixed with
r"pattern"
) to avoid Python treating backslashes (\
) as escape characters. - Use the regex functions: Functions like
re.search()
,re.match()
,re.findall()
,re.sub()
, and others can be used to apply the pattern to a string.
Basic Syntax for Writing a Regex Pattern:
- Literal Characters: Match the characters as they appear (e.g.,
r"abc"
). - Metacharacters: Special characters like
.
(any character),\d
(digit),\w
(word character),\s
(whitespace), etc. - Quantifiers: Specify how many times a character/group should occur. E.g.,
*
(0 or more),+
(1 or more),{n}
(exactly n times), etc. - Anchors: Mark positions in the string. E.g.,
^
(start of string),$
(end of string).
Example of Groups and Backreferences using re.search()
python"># Using groups to capture parts of a pattern
pattern = r"(\d{3})-(\d{2})-(\d{4})"
text = "SSN: 123-45-6789"match = re.search(pattern, text)
if match:print(match.group(1)) # Output: 123print(match.group(2)) # Output: 45print(match.group(3)) # Output: 6789
Example of using re.findall()
:
python"># Finding all occurrences of a pattern
text = "My phone number is 123-456-7890, and my office number is 098-765-4321."
pattern = r"\d{3}-\d{3}-\d{4}" # Matches phone numbersmatches = re.findall(pattern, text)
print(matches) # Output: ['123-456-7890', '098-765-4321']
Example of using re.sub()
:
python"># Replacing digits with asterisks
text = "My password is 12345."
pattern = r"\d"# Replace each digit with '*'
masked_text = re.sub(pattern, "*", text)
print(masked_text) # Output: My password is *****.
re.match()
re.match()
checks if the pattern matches at the start of the string.- If there is no match at the beginning,
None
is returned. - Use
match.group()
to extract the matched string if a match is found. - Can be replaced with
re.search()
by anchoring the pattern to the start of the string using the^
(caret) metacharacter.
Special Characters - see CSDN
Answer Generated by OpenAI's ChatGPT"