Create Immutable, Hashable Sets with Python Frozenset

def calculate_permissions(user_roles):
    """
    Determines effective permissions based on a frozenset of user roles.
    Uses a cache for performance.
    """
    # A dictionary to cache permissions for specific role combinations
    # frozenset is used as the key because regular sets are unhashable
    _permission_cache = {}

    # Define some base permissions for roles
    ROLE_PERMISSIONS = {
        'admin': frozenset(['view_dashboard', 'manage_users', 'edit_content']),
        'editor': frozenset(['edit_content', 'upload_media']),
        'viewer': frozenset(['view_content']),
        'guest': frozenset(['view_public_content'])
    }

    roles_frozenset = frozenset(user_roles)

    if roles_frozenset in _permission_cache:
        print(f"Cache hit for roles: {user_roles}")
        return _permission_cache[roles_frozenset]

    print(f"Calculating permissions for roles: {user_roles}")
    effective_permissions = frozenset()
    for role in roles_frozenset:
        effective_permissions = effective_permissions.union(ROLE_PERMISSIONS.get(role, frozenset()))

    _permission_cache[roles_frozenset] = effective_permissions
    return effective_permissions

# Example usage for a web application scenario
admin_perms = calculate_permissions(['admin', 'editor'])
print("Admin+Editor Permissions:", sorted(list(admin_perms)))

viewer_perms = calculate_permissions(['viewer'])
print("Viewer Permissions:", sorted(list(viewer_perms)))

# Calling with the same roles should result in a cache hit
admin_editor_perms_cached = calculate_permissions(['editor', 'admin']) # Order doesn't matter for sets
print("Admin+Editor Permissions (cached):", sorted(list(admin_editor_perms_cached)))

guest_perms = calculate_permissions(['guest'])
print("Guest Permissions:", sorted(list(guest_perms)))