Use subprocess instead of os.system

[davidism]

There are various places, mostly in _termui_impl, that use os.system. Python has recommended using subprocess (call, Popen) instead for quite some time. Replace all occurrences of os.system with subprocess.call or Popen, passing a list of args (not a string command). This will require a bit of care since there's a few places that write command strings that can't be directly translated to args lists, and we should ensure the expected commands continue to work on Windows, Mac, and Linux.

[mitsuhiko]

What's the benefit of using subprocess here? Specially the shell mode of subprocess (which woudl be needed here) has the same issues as os.system

[jwodder]

@mitsuhiko Why would the shell mode be needed? The only shell constructs currently used in the os.system() calls are redirects (which can be reproduced with the stdout= and stderr= arguments to Popen()) and subshelling with (cmd) (which appears to be superfluous, and even if it's not, it should be reproduceable with subprocess.call(['sh', '-c', 'cmd'])). Is this about the idiosyncratic command-splitting on Windows?

[mitsuhiko]

The pager support is directly taken from pyhelp in the stdlib. Last time I tried to replace it with subprocess I ran into a lot of annoying issues on windows. Can't remember the details but effectively it didn't work like I wanted unless it ran through a shell indirection.

[harivamsi9]

Hi, I wanna fix this issue, Can i know what is the current status? and why was this stalled