What's the point of this code pattern?

Question

Hi,

I was trying to create a python wrapper for an tk extension, so I looked at Tkinter.py to learn how to do it.

While looking at that file, I found the following pattern appears a lot of times: an internal method (hinted by the leading "_" in the method name) is defined, then a public method is defined just to be the internal method.

I want to know what's the benefit of doing this.

For example, in the code for class Misc:

def _register(self, func, subst=None, needcleanup=1):
    # doc string and implementations is removed since it's not relevant
register = _register

Thank you.

Answer 1

From PEP8

In addition, 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.

Answer 2

Well, I'm supposing, there could be another internal callable, that could've been used, it just didn't make it to the version you have. Generally, I think it is a good idea - you expose one symbol publically and internally it can be anything, a real method, a stubbed out method, a debug version of the method, anything.

Answer 3

Sometimes, you may want to change a method's behavior. For example, I could do this (hypothetically within the Misc class):

def _another_register(self, func, subst=None, needcleanup=1):
    ...

def change_register(self):
    self.register = self._another_register

def restore_register(self):
    self.register = self._register

This can be a pretty handy way to alter the behavior of certain pieces of code without subclassing (but it's generally not advisable to do this kind of thing except within the class itself).