Extract line differences in python.

extract_line_differences.py

import difflib

def extract_line_differences(source: str, modified: str) -> dict:
    """
    Extracts line-level differences between two multi-line strings and returns a dictionary where:
      - For replacements: key is the differing block of lines in the source and 
        value is the corresponding block of lines in the modified string.
      - For deletions: key is the block of lines deleted from the source, value is an empty string.
      - For insertions: key is a string indicating the insertion location (e.g., "INSERT_AT_LINE_#")
        and value is the inserted block of lines from the modified string.
        
    Parameters:
        source (str): The original multi-line string.
        modified (str): The modified multi-line string.
        
    Returns:
        dict: A dictionary with line-level differences.
    """
    diff_dict = {}
    # Split strings into lists of lines.
    source_lines = source.splitlines()
    modified_lines = modified.splitlines()
    
    # Compare the lists of lines.
    matcher = difflib.SequenceMatcher(None, source_lines, modified_lines)
    for tag, i1, i2, j1, j2 in matcher.get_opcodes():
        if tag == 'equal':
            continue  # Lines are identical.
        elif tag == 'replace':
            # A block of source lines was replaced by a block of modified lines.
            key = "\n".join(source_lines[i1:i2])
            value = "\n".join(modified_lines[j1:j2])
            diff_dict[key] = value
        elif tag == 'delete':
            # A block of lines in the source was deleted.
            key = "\n".join(source_lines[i1:i2])
            diff_dict[key] = ""
        elif tag == 'insert':
            # New lines were inserted in the modified string.
            key = f"INSERT_AT_LINE_{i1}"
            value = "\n".join(modified_lines[j1:j2])
            diff_dict[key] = value

    return diff_dict