Why can't I restore my redirected stdout?

[Donn Cave]

Quoth "Raymond Ng Tong Leng" <think2 at pd.jaring.my>:
| I am trying to implement a verbose and quiet mode in my Python script. So I
| wrote the following class:
|
| class Quiet:
|     def write(self, data):
|         pass
|
| Then I set sys.stdout to Quiet by:
|
| >>> sys.stdout = Quiet()
| >>> print 'hello'
| >>>
|
| 'hello' doesn't come out which is what I want. But, when I tried to restore
| sys.stdout's original settings:
|
| >>> sys.stdout = sys.__stdout__
| >>> print 'hello'
| >>>
|
| 'hello' is not printed either! How do you restore sys.stdout to its original
| settings? Also, I was wondering, are there other ways to suppress
| sys.stdout? I'm just curious whether I could suppress sys.stdout without
| redirecting to a class. It seems to me that I should be able to redirect
| sys.stdout to a null device or something. Thanks!

I'm not familiar with sys.__stdout__, maybe someone else knows that one.

If you're on UNIX, you can dup() the file descriptors around underneath
stdout, for this effect.  I append an example.

	Donn Cave, donn at u.washington.edu
----------------------------------------
import os
import sys

class Outs:
	def __init__(self):
		self.streams = []
	def setdevice(self, filename):
		#  Open an existing file, like "/dev/null"
		fd = os.open(filename, os.O_WRONLY)
		self.setfd(fd)
	def setfile(self, filename):
		#  Open a new file.
		fd = os.open(filename, os.O_WRONLY|os.O_CREAT, 0660);
		self.setfd(fd)
	def setfd(self, fd):
		ofd = os.dup(1)	      #  Save old stream on new unit.
		self.streams.append(ofd)
		sys.stdout.flush()    #  Buffered data goes to old stream.
		os.dup2(fd, 1)        #  Open unit 1 on new stream.
		os.close(fd)          #  Close other unit (look out, caller.)
	def unset(self):
		#  Restore previous output stream.
		if self.streams:
			sys.stdout.flush()
			os.dup2(self.streams[-1], 1)
			os.close(self.streams[-1])
			del self.streams[-1]