I've been thinking about it, and I think even though it would be a slight 
change to the API, I agree with Winfried that the default value for 
bufsize should be -1, not 0.  In my own use of os.popen and friends, 
almost all the time I use them to process the output of a traditional Unix 
pipeline, which means the output will be plain text, line buffered.  In 
those cases it makes absolutely no sense to read from the pipe one 
character at a time.

S