__init__.py 文件源码

def choice(argument, values):
    """
    Directive option utility function, supplied to enable options whose
    argument must be a member of a finite set of possible values (must be
    lower case).  A custom conversion function must be written to use it.  For
    example::

        from docutils.parsers.rst import directives

        def yesno(argument):
            return directives.choice(argument, ('yes', 'no'))

    Raise ``ValueError`` if no argument is found or if the argument's value is
    not valid (not an entry in the supplied list).
    """
    try:
        value = argument.lower().strip()
    except AttributeError:
        raise ValueError('must supply an argument; choose from %s'
                         % format_values(values))
    if value in values:
        return value
    else:
        raise ValueError('"%s" unknown; choose from %s'
                         % (argument, format_values(values)))