I have this function of getting modified files in Azure Devops PR:

def fetch_pr_diff(pr_id):
    try:
        # Establish connection and get the Git client
        connection = get_azure_devops_connection()
        git_client = connection.clients.get_git_client()
        
        # Retrieve pull request iterations
        iterations = git_client.get_pull_request_iterations(
            repository_id=repository_id,
            project=project_name,
            pull_request_id=pr_id
        )
        
        # Get the latest iteration
        latest_iteration = max(iterations, key=lambda x: x.id)
        
        # Fetch changes for the latest iteration
        iteration_changes = git_client.get_pull_request_iteration_changes(
            repository_id=repository_id,
            project=project_name,
            pull_request_id=pr_id,
            iteration_id=latest_iteration.id
        )
        
        # Initialize the diff content
        diff_content = ""
        
        # Loop through the changes to extract diffs for each file
        for change in iteration_changes.change_entries:
            if change.additional_properties['item'] is not None:  # Only process items with valid file information
                change = change.additional_properties['item']
                file_path = change['path']
                
                # Check the change type (e.g., modified, added, deleted)
                change_type = iteration_changes.change_entries[0].additional_properties['changeType']
                
                # Process modified files
                if change_type in ['edit', 'add']:
                    # Fetch the file content of the latest version
                    file_content = git_client.get_item_content(
                        repository_id=repository_id,
                        project=project_name,
                        path=file_path
                    )
                    file_content_ = ''.join(chunk.decode('utf-8') for chunk in file_content)
                    # Add file details to the diff content
                    diff_content += f"File: {file_path}n"
                    diff_content += f"Change Type: {change_type}n"
                    diff_content += f"Content:n{file_content_}nn"
                elif change_type == 'delete':
                    # If the file is deleted, just log the deletion
                    diff_content += f"File: {file_path}n"
                    diff_content += f"Change Type: {change_type}n"
                    diff_content += "Content: File deleted.nn"

        return diff_content

the problem is that i want fetch only the modified part, and not the whole file.
how can i just get the modified part between the commited file and the master?
thanks!