在一个模块中，我应该使用一个、两个或没有下划线来表示用户不应该调用的助手函数吗？

python样式指南pep-8建议使用一个前导下划线。

The following special forms using leading or trailing underscores are recognized (these can generally be combined with any case convention):

• _single_leading_underscore: weak"internal use" indicator. E.g. from M import * does not import objects whose name starts with an underscore.
• ...

可能只有一个下划线，但这取决于具体情况。

具体来说，python风格指南(pep 8)指出：

_single_leading_underscore: weak"internal use" indicator. E.g. from M import * does not import objects whose name starts with an underscore.

__double_leading_underscore: when naming a class attribute, invokes name mangling (inside class FooBar, __boo becomes _FooBar__boo; see below).

另请参阅此问题以获得更长的答案：对象名称前的单下划线和双下划线的含义是什么？