Python Regular Expressions (RegEx) with examples

Regular Expressions (regex) are patterns used to match character combinations in strings. Let’s go through some examples using Python’s re module.

1. Importing the re module:

   import re

    

2. Basic Match:

   pattern = r"hello" 
   text = "hello world" 
   match = re.search(pattern, text) 
   if match: 
      print("Found:", match.group())

    

3. • .: Matches any character except newline.
   • ^: Matches the start of the string.
   • $: Matches the end of the string.
   • *: Matches 0 or more repetitions of the preceding character.
   • +: Matches 1 or more repetitions of the preceding character.
   • ?: Matches 0 or 1 repetition of the preceding character.
   • {m,n}: Matches from m to n repetitions of the preceding character.
     

     Using Metacharacters:

   pattern = r"he..o"
   text = "hello world"
   
   match = re.search(pattern, text)
   if match:
       print("Found:", match.group())
   

    

4. • \d: Matches any digit (equivalent to [0-9]).
   • \D: Matches any non-digit.
   • \w: Matches any word character (equivalent to [a-zA-Z0-9_]).
   • \W: Matches any non-word character.
   • \s: Matches any whitespace character.
   • \S: Matches any non-whitespace character.
     

     Character Classes:

   pattern = r"\d+"
   text = "There are 42 apples"
   
   match = re.search(pattern, text)
   if match:
       print("Found:", match.group())
   

5. Grouping and Capturing:

   pattern = r"(hello) (world)"
   text = "hello world"
   
   match = re.search(pattern, text)
   if match:
       print("Found:", match.group())
       print("Group 1:", match.group(1))
       print("Group 2:", match.group(2))
   

    

6. Finding All Matches:

   pattern = r"\d+"
   text = "There are 42 apples and 35 oranges"
   
   matches = re.findall(pattern, text)
   print("All Matches:", matches)
   

    

7. Replacing Text:

   pattern = r"apples"
   replacement = "bananas"
   text = "I have apples"
   
   new_text = re.sub(pattern, replacement, text)
   print("New Text:", new_text)
   

    

8. Splitting Strings:

   pattern = r"\s+"
   text = "This is a test"
   
   split_text = re.split(pattern, text)
   print("Split Text:", split_text)