Wehn copying os.environ usinf copy.copy(), any manipulation on the copied object will change os.environment, too.

$ python
Python 2.7.3 (default, Apr 22 2012, 07:46:58) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import copy, os
>>> os.environ['TITI']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/UserDict.py", line 23, in __getitem__
    raise KeyError(key)
KeyError: 'TITI'
>>> env = copy.copy(os.environ)
>>> env['TITI'] = 'in den Ferien'
>>> os.environ['TITI']
'in den Ferien'
>>> 

Strictly speaking, this is correct, as the os.environment class is meant to manipulate the environment in the background. But user's expectation is different: he thinks, manipulating the copied object is save and does not effect the environment.

os.environ is not a dictionary, so it isn't all that surprising that a shallow copy doesn't behave like a shallow copy of a dictionary.  deepcopy does what you'd expect, as does os.environ.copy().

Perhaps it is worth improving this by adding a __copy__ method to os.environ.  Someone would need to propose a patch, and it would be an enhancement.

Here's a patch.

A new patch with tests.

I agree with David that copy(os.environ) is rather ambiguous. I think the preferred idiom should be to call dict(os.environ).
As for __copy__, I don't know what it should do: perhaps simply raise an error when copying is attempted?

Well, I think the fact that os.environ.copy is explicitly supported (and does indeed do dict(os.environ)) is an argument in favor of giving that same meaning to copy(os.environ).  I think that follows the principle of least surprise.

If add support for the copy protocol, consider also adding support for deepcopying and pickling.

[Antoine]
> I agree with David that copy(os.environ) is rather ambiguous.
> I think the preferred idiom should be to call dict(os.environ).
> As for __copy__, I don't know what it should do: perhaps
> simply raise an error when copying is attempted?

FWIW, I concur with Antoine on every point.  Also, raising an error when copying seems reasonable ("refuse the temptation to guess" at what the user intended).

patch looks OK.
But I prefer `__deepcopy__ = __copy__ = copy`.

I don't know how to support pickling. (should unpickled object
reference os.environ, or copied dict?)
I feel it is different issue.

That patch would be fine except that I really agree with Antoine that an error should be raised.

I agree.
os.environ is not dict, it's a proxy of "current" environment which
is not copyable.
So I agree to copy.copy() shouldn't copy os.environ implicitly.