Redirect question

[Alex Martelli]

Karsten Weinert wrote:

> Well, after solving my error in the Redirect class with all your help,
> I now encountered a new problem. Here is the program:
> 
> import sys, win32ui
> 
> class Redirect:
>   def __init__(self):
>     self.s=""
>   def write(self, s):
>     self.s+=s
>   def flush(self):
>     win32ui.MessageBox(self.s)
> 
> sys.stdout = Redirect()
> sys.stderr = Redirect()
> print 'Hidey Ho'
> print "Hidey hidey hidey ho"
> sys.stdout.flush() # is displayed
> # from here, no output is produced, e.g. no messagebox
> assert 1==0, "Impossible Assertion"
> sys.stderr.flush()
> 
> What am I doing wrong? Enclosing the assert statement with try/finally
> or try/except only displays an empty message box.
> 
> Kind regards,
> Karsten

The sys.stderr.flush call can never execute, since it follows a statement 
that raises an exception.

To follow in more detail what is happening, I suggest you add print calls 
(to sys.__stdout__ for example, to make sure they're going to get out) 
tracing the behaviour of self.s in Redirect's methods, and run the whole 
script via python.exe, not pythonw.exe, from a console (aka "Dos Box").


Alex