Check if element is in a non-uniform N-d Python list [Python]

in_nD_list.py

def in_nD_list(search_list, key):
    for element in search_list:
        if isinstance(element, str):
            if key in element:
                break
        else:
            if in_nD_list(element, key):
                break
    else:
        return False

    return True

Needed this for my Brainfuck interpreter!