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Re: Not possible to hide local variables

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Steven D'Aprano <steve+comp.lang.python@pearwood.info>:

> The convention is, if the caller messes with your private attributes
> or variables, and their code breaks, they have nobody to blame but
> themselves, and we are allowed to laugh at them. We're consenting
> adults here.

I would take it further: as a rule, user code should not think of
modifying the contents of an object unless it is clearly documented as a
supported operation. IOW, you should consider all attributes private, or
at least read-only.

BTW, the principle is actually enforced for some objects:

   >>> "hello".join = lambda *x: "world"
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   AttributeError: 'str' object attribute 'join' is read-only
   >>> "hello".joinn = lambda *x: "world"
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   AttributeError: 'str' object has no attribute 'joinn'
   >>> "hello".__setattr__ = lambda *x: None
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   AttributeError: 'str' object attribute '__setattr__' is read-only


A tougher issue is with encapsulation. A derived class might
accidentally step on the toes of the base class by redefining an
attribute:

========================================================================
class Base:
    def __init__(self):
        self._secret = 17

    def divulge_secret(self):
        return self._secret

class Derived(Base):
    def __init__(self):
        self._secret = 1

print(Derived().divulge_secret())
========================================================================

which outputs 1.


Marko

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Thread

Not possible to hide local variables Cecil Westerhof <Cecil@decebal.nl> - 2015-04-28 09:33 +0200
  Re: Not possible to hide local variables Ethan Furman <ethan@stoneleaf.us> - 2015-04-28 00:56 -0700
    Re: Not possible to hide local variables Cecil Westerhof <Cecil@decebal.nl> - 2015-04-29 08:16 +0200
      Re: Not possible to hide local variables Michael Torrie <torriem@gmail.com> - 2015-04-29 21:10 -0600
  Re: Not possible to hide local variables Chris Angelico <rosuav@gmail.com> - 2015-04-28 18:06 +1000
    Re: Not possible to hide local variables Cecil Westerhof <Cecil@decebal.nl> - 2015-04-29 08:25 +0200
      Re: Not possible to hide local variables Chris Angelico <rosuav@gmail.com> - 2015-04-29 17:36 +1000
  Re: Not possible to hide local variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-28 18:37 +1000
    Re: Not possible to hide local variables Chris Angelico <rosuav@gmail.com> - 2015-04-28 18:44 +1000
    Re: Not possible to hide local variables Marko Rauhamaa <marko@pacujo.net> - 2015-04-28 12:20 +0300
    Re: Not possible to hide local variables Cecil Westerhof <Cecil@decebal.nl> - 2015-04-29 08:32 +0200
      Re: Not possible to hide local variables Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-30 14:05 +1000
        Re: Not possible to hide local variables Marko Rauhamaa <marko@pacujo.net> - 2015-04-30 08:10 +0300
          Re: Not possible to hide local variables Chris Angelico <rosuav@gmail.com> - 2015-04-30 16:01 +1000
  Re: Not possible to hide local variables Cecil Westerhof <Cecil@decebal.nl> - 2015-04-29 08:14 +0200
  Re: Not possible to hide local variables Grant Edwards <invalid@invalid.invalid> - 2015-04-29 14:16 +0000
    Re: Not possible to hide local variables Dave Angel <davea@davea.name> - 2015-04-29 22:31 -0400
    Re: Not possible to hide local variables Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-04-30 08:53 -0400
      Re: Not possible to hide local variables Cecil Westerhof <Cecil@decebal.nl> - 2015-04-30 16:50 +0200

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