Python, Keyboard Interrupt, and Windows

[Gerowen]

So I'm writing my own launcher for youtube-dl just for my own personal use, and to familiarize myself with Python a little bit more.  When I run it in Linux, it works normally, and if I cancel a download with CTRL+C, the "Interrupted by User" error message appears.  If I run it in Windows, it works normally, except the "Interrupted by User" error message does not appear when I cancel a download with CTRL+C.  The other error messages such as the "Invalid URL" one works, so I know it's making down into the "elif download is not 0:" portion, but that one error message doesn't appear.

 

It's not the end of the world, and I'm suspecting this has something to do with the way Windows, or the Windows version of youtube-dl, handles the CTRL+C keyboard interrupt.  Here's the block of code that launches the download and then displays messages according to the outcome.

 

Code Snippet

 

If you have issues opening the link let me know and I'll re-do it, but Neowin's code bracket didn't recognize any of the indentions, and it looked a bit confusing, so I thought this would be easier to read.

[Gerowen]

Even if a keyboard interrupt spit out an error code other than the "2" specified, it should still get caught by the "else" statement that issues the "Unknown error" window, but not even that comes up, it just cancels the download but doesn't tell the user anything.

[Lant]

You need to wrap your code in a try..except and catch KeyboardInterrupt
 

try:
    <yourcode>
except KeyboardInterrupt as e:
    print(e)

other tips:

1. I wouldn't use "is" to compare numbers, use "==". The reason this works is that for performance reasons CPython creates objects for the first 256 ints and uses them whenever you have a value in that range.
The only time you tend to use "is" is when you want to check if something is None (by "is None").

2. Also avoid "is" for strings, use "==" instead, it should only work if those strings are interned. See http://stackoverflow.com/questions/2988017/string-comparison-in-python-is-vs for some more information.

3. os.system works, but you should probably replace it with subprocess.call. The subprocess module has more features and is intended to be a replacement for a number of older modules and functions (including os.system).

 

4. Use os.path to manipulate your paths to reduce the chance of errors

[snaphat (Myles Landwehr) Member]

You probably should just setup a signal handler for your main process: http://docs.python.org/2/library/signal.html, use subprocess.popen().wait(), and then manually terminate the process if SIGINT is sent. The reason being is that this will make termination handling consistent across platforms.

 

If you go with the exception solution you may or may not need to terminate the subprocess manually in Windows. Another thing to note is that there are subtle differences in interrupt behavior between os.system() and subprocess.call(): http://stackoverflow.com/questions/18739821/keyboard-interrupts-and-os-system-vs-subprocess-call that can affect you depending on what you are doing.