Find all the patterns of "1(0+)1" in a given string using Python Regex

In this tutorial, we will find all occurrences of the pattern "1(0+)1" in a string using Python's regex module. The re module provides powerful pattern matching capabilities for text processing.

The pattern "1(0+)1" represents a literal string containing the number 1, followed by parentheses with "0+" inside, and ending with another 1.

Example Input and Output

Input:
string = "Sample 1(0+)1 string with 1(0+)1 unnecessary patterns 1(0+)1"

Output:
Total number of pattern matches are 3
['1(0+)1', '1(0+)1', '1(0+)1']

Algorithm

Follow these steps to find the pattern:

1. Import the re module
2. Initialize the input string
3. Create a regex pattern using re.compile() with proper escaping
4. Use findall() method to get all matches
5. Display the count and matched patterns

Implementation

import re

# Initialize the string
string = "Sample 1(0+)1 string with 1(0+)1 unnecessary patterns 1(0+)1"

# Create regex pattern - escape special characters
regex = re.compile(r"1\(0\+\)1")

# Find all matching patterns
result = regex.findall(string)

# Print results
print(f"Total number of pattern matches are {len(result)}")
print(result)

Total number of pattern matches are 3
['1(0+)1', '1(0+)1', '1(0+)1']

Understanding the Regex Pattern

The regex pattern r"1\(0\+\)1" breaks down as follows:

1     - Matches literal character '1'
\(    - Matches literal '(' (escaped)
0     - Matches literal character '0'  
\+    - Matches literal '+' (escaped)
\)    - Matches literal ')' (escaped)
1     - Matches literal character '1'

Alternative Approach Using re.findall() Directly

import re

string = "Sample 1(0+)1 string with 1(0+)1 unnecessary patterns 1(0+)1"

# Direct approach without compiling
matches = re.findall(r"1\(0\+\)1", string)

print(f"Found {len(matches)} matches:")
for i, match in enumerate(matches, 1):
    print(f"Match {i}: {match}")

Found 3 matches:
Match 1: 1(0+)1
Match 2: 1(0+)1
Match 3: 1(0+)1

Key Points

Remember to escape special regex characters like (, ), and + when searching for literal text. Use raw strings (r"") to avoid double escaping in Python.

Conclusion

Using Python's re module, you can easily find literal patterns by properly escaping special characters. The findall() method returns all non-overlapping matches as a list.