On 29Dec2008 11:11, Grebekel <grebe...@gmail.com> wrote: | I have recently noticed that print statements ending with a comma are | not immediately flushed.
I will warn you that neither are the more common uncommaed print statements, except on a terminal. | [...] Example: | <code> | print 'Take a walk, because this will take a while...', | i = 0 | while i < 10**10: | i += 1 | print "we're done!" | </code> | | Here the first string is not printed until the second print statement. [...] | Using sys.std.flush after the print fixes this issue, but doing so | each time seems cumbersome and somewhat counterintuitive. | Is there some reasoning behind this behavior or is it a bug? It's correct behaviour. The python print etc is layered on the C library stdio. A stdio stream can be buffered in three standard ways: unbuffered, line buffered and block buffered. On UNIX, on a terminal, stdout is normally line buffered: output is flushed when a newline is encoutered in the data, and this is pleasing to humans. Conversely, is stdout is _not_ attached to a terminal it will be block buffered by default; output is only flushed when the buffer is filled. This is much more _efficient_ in terms of I/O and program activity. By contrast, again by default, stderr is normally unbuffered. Being reserved for error messages, immediate output (before your program explodes:-) is considered more important than system efficiency. So you should sys.stdout.flush() if you want data output right now. For many purposes it is better to let the default behaviour obtain. Also, I suugest that progress reporting such as your be written to stderr anyway. It will appear in a timely fashion, and will also thus not pollute the output stream. Consider: your-program >datafile or your-program | process the output data... Sending your progress reports to stdout puts junk in the data stream. Cheers, -- Cameron Simpson <c...@zip.com.au> DoD#743 http://www.cskk.ezoshosting.com/cs/ Gentle suggestions being those which are written on rocks of less than 5lbs. - Tracy Nelson in comp.lang.c -- http://mail.python.org/mailman/listinfo/python-list
