def PtknsToStr(path_tokens):
    """
    There are three ways to store paths:
      As a single string: '/Protein/Phe/Ca'  <- the format entered by the user
      As a list of tokens ['Protein', 'Phe', 'Ca'] <- split into tokens
      As a list of nodes in a tree (pointers to nodes in a tree hierarchy)
    This function converts between the first two formats.
    """
    text = ''
    if len(path_tokens) > 0:
        text = path_tokens[0]
        for i in range(1, len(path_tokens)):
            text += '/' + path_tokens[i]
    else:
        text = ''
    return text