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Re: AttributeError in "with" statement (3.2.2)

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Steve Howell wrote:

> I'm using Python 3.2.2, and the following program gives me an error
> that I don't understand:
> 
> class Foo:
>   pass
> 
> foo = Foo()
> foo.name = "Steve"
> 
> def add_goodbye_function(obj):
>   def goodbye():
>     print("goodbye " + obj.name)
>   obj.goodbye = goodbye
> 
> add_goodbye_function(foo)
> foo.goodbye() # outputs goodbye Steve
> foo.__exit__ = foo.goodbye
> foo.__exit__() # outputs goodbye Steve
> 
> with foo: # fails with AttributeError:  __exit__
>   print("doing stuff")
> 
> I am dynamically adding an attribute __exit__ to the variable foo,
> which works fine when I call it directly, but it fails when I try to
> use foo as the expression in the with statement.  Here is the full
> output:
> 
>> python3 with.coffee
> goodbye Steve
> goodbye Steve
> Traceback (most recent call last):
>   File "with.coffee", line 17, in <module>
>     with foo: # fails with AttributeError:
> AttributeError: __exit__

If you don't know it yet, contextlib.contextmanager offers a highlevel 
alternative:

>>> @contextmanager
... def goodbye(obj):
...     try:
...             yield obj
...     finally:
...             print("goodbye", obj.name)
...
>>> with goodbye(Foo()) as foo:
...     print("hello", foo.name)
...
hello Steve
goodbye Steve

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AttributeError in "with" statement (3.2.2) Steve Howell <showell30@yahoo.com> - 2011-12-13 21:42 -0800
  Re: AttributeError in "with" statement (3.2.2) Eric Snow <ericsnowcurrently@gmail.com> - 2011-12-13 23:05 -0700
  Re: AttributeError in "with" statement (3.2.2) Terry Reedy <tjreedy@udel.edu> - 2011-12-14 01:29 -0500
    Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-14 08:01 +0000
      Re: AttributeError in "with" statement (3.2.2) 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-14 08:08 -0800
        Re: AttributeError in "with" statement (3.2.2) 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-14 08:28 -0800
      Re: AttributeError in "with" statement (3.2.2) Steve Howell <showell30@yahoo.com> - 2011-12-14 09:16 -0800
      Re: AttributeError in "with" statement (3.2.2) Terry Reedy <tjreedy@udel.edu> - 2011-12-14 18:13 -0500
        Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-15 05:01 +0000
          Re: AttributeError in "with" statement (3.2.2) MRAB <python@mrabarnett.plus.com> - 2011-12-15 05:15 +0000
            Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-15 07:21 +0000
            Re: AttributeError in "with" statement (3.2.2) Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-12-16 09:34 +1300
          Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-15 07:47 +0000
          Re: AttributeError in "with" statement (3.2.2) Steve Howell <showell30@yahoo.com> - 2011-12-15 05:35 -0800
            Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-16 03:34 +0000
          Re: AttributeError in "with" statement (3.2.2) Terry Reedy <tjreedy@udel.edu> - 2011-12-15 19:39 -0500
            Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-16 09:22 +0000
              Re: AttributeError in "with" statement (3.2.2) Terry Reedy <tjreedy@udel.edu> - 2011-12-16 17:05 -0500
                Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-17 01:26 +0000
                Re: AttributeError in "with" statement (3.2.2) Terry Reedy <tjreedy@udel.edu> - 2011-12-17 21:09 -0500
              Re: AttributeError in "with" statement (3.2.2) Ethan Furman <ethan@stoneleaf.us> - 2011-12-16 15:26 -0800
                Re: AttributeError in "with" statement (3.2.2) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-17 03:05 +0000
              Re: AttributeError in "with" statement (3.2.2) Ethan Furman <ethan@stoneleaf.us> - 2011-12-16 16:34 -0800
  Re: AttributeError in "with" statement (3.2.2) Peter Otten <__peter__@web.de> - 2011-12-14 11:02 +0100
  Re: AttributeError in "with" statement (3.2.2) Eric Snow <ericsnowcurrently@gmail.com> - 2011-12-14 09:56 -0700
  Re: AttributeError in "with" statement (3.2.2) Lie Ryan <lie.1296@gmail.com> - 2011-12-15 06:14 +1100
  Re: AttributeError in "with" statement (3.2.2) Eric Snow <ericsnowcurrently@gmail.com> - 2011-12-14 12:46 -0700

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