On Sun, Jan 29, 2017 at 3:15 AM, Steve D'Aprano <steve+pyt...@pearwood.info> wrote: > On Sat, 28 Jan 2017 10:50 pm, Chris Angelico wrote: > >> On Sat, Jan 28, 2017 at 9:49 PM, Steve D'Aprano >> <steve+pyt...@pearwood.info> wrote: >>> The terminal size doesn't change just because I'm piping output to >>> another process. Using the terminal size as a proxy for "being piped" is >>> sheer insanity. >> >> In a sense, there _is no_ terminal size when you're being piped to >> another process. > > In which sense, and why do you think it is relevant? > > There clearly is a terminal, because that's where I'm running the code. > Regardless of whether I pipe it to grep or cat or something else, the > output from *that* process still ends up in the same terminal that I typed > the command in.
No, not automatically. I've written plenty of programs that accept input via a pipe and don't display any of it. Just because someone types "command1 | command2", you can't assume that the terminal command2 is outputting to is the same size as the one command1 should be outputting to. >> etc, etc, etc, etc. It's >> not a proxy for "being piped" - it's that when your output isn't going >> to a terminal, asking "what is my terminal size" isn't particularly >> productive. > > Then explain why os.get_terminal_size() returns the correct answer. > > The output might not be going to a terminal (not directly at least) but the > question isn't "what's the size of the terminal that output is going to". > The question is "what's the size of the terminal that this process is > running in", and that has an answer regardless of where output is piped. Processes aren't always running "in" terminals, though. That's my point. A terminal is not a fundamental feature of a process. >> Would you expect a cronjob to use the terminal size when you >> most recently edited crontab? No. > > Of course not -- the terminal where you edited crontab is not where the > process is running. Why would it be the least bit relevant? So where *is* that process running? What terminal is it in? Don't you see how similar this is to the pipe situation - sure, there might be a terminal that the program was invoked from, but it's utterly irrelevant to how the program actually runs. >> You might well be a completely background process. > > And if that background process is running in a terminal? What's your point? Background processes don't have terminal access. Whether it's a daemon or something started as "commandname >/dev/null 2>/dev/null </dev/null &" from bash, it doesn't have access to a terminal. Please don't assume that every program has a controlling UI. I get enough of that mentality from the people I support on Windows, where the fundamental assumption of people seems to be that there's a GUI for everything. There isn't. And there isn't always a terminal either. Processes in the middle of pipelines *do not have* terminals. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
