[issue1175] .readline() has bug WRT nonblocking files

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[issue1175] .readline() has bug WRT nonblocking files

Guido van Rossum added the comment: readline() goes through C stdio which makes it impossible to get non-blocking I/O right. You should be using raw os.read() calls (until python 3000 which will remove Python's reliance on C stdio). -- nosy: +gvanrossum resolution: -> wont fix status: o

[issue1175] .readline() has bug WRT nonblocking files

Sean Reifschneider added the comment: Arguably, you should be using "select" and "read" (instead of readline) for this operation. That's what I've done in the past when doing something similar. Specifically, I believe I have looped reading into a buffer with read, and using select with a timeou

[issue1175] .readline() has bug WRT nonblocking files

Alex Burr added the comment: I don't need to change my code as I have now worked round the problem, but for an example of why someone might want nonblocking mode: It was not actually in order to do any more work, but because I was managing both input and output to gdb in one thread (for simplici

[issue1175] .readline() has bug WRT nonblocking files

Sean Reifschneider added the comment: Why are you putting the file in non-blocking mode? Why not just reading in blocking mode? If you want to do other work when a line is not available, you could use select to check to see if there's data ready via a small or 0 timeout. __

[issue1175] .readline() has bug WRT nonblocking files

Alex Burr added the comment: The exception would count as a warning if it wasn't EGAIN. One expects to catch EGAIN and try again. The current situation is unfortunate because it *nearly* works. My scenario is: I'm driving GDB/MI via popen2.Popen3 ( gdbCommand, False,1). It works for most GDB com

[issue1175] .readline() has bug WRT nonblocking files

Sean Reifschneider added the comment: Doesn't the exception count as warning the user? We probably don't want to change readline to return a partial line in this case. An exception could be added for EGAIN that includes the partial line. Another option would be to just document the behavior fo

[issue1175] .readline() has bug WRT nonblocking files

New submission from Alex Burr: If you have made a file nonblocking using fcntl.fcntl, .readline() will discard the start of a line if you get EGAIN. It should attach the partial line to the exception somehow - or at least warn the user. I observe this on 2.3.5, but the same code exists in TRUNK