Hi Chris,

On 07.01.18 18:18, Chris Angelico wrote:

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Redirecting this part of the conversation to python-ideas.

On Mon, Jan 8, 2018 at 3:17 AM, Christian Tismer wrote:

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As a side note: In most cases where shell=True is found, people seem to need evaluation of the PATH variable. To my understanding,

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from subprocess import call call(("ls",)) works in Linux, but (with dir) not in Windows. But that is misleading because "dir" is a builtin command but "ls" is not. The same holds for "del" (Windows) and "rm" (Linux). That's exactly what shell=True is for - if you want a shell feature, you use the shell. What exactly would emulate_shell do? Would it simply do a $PATH or %PATH% search, but otherwise function as shell=False? Would it process redirection? Would it handle interpolations? I think not, from your description:

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Perhaps it would be a good thing to emulate the builtin programs in python by some shell=True replacement (emulate_shell=True?) to match the normal user expectations without using the shell? but it becomes difficult to draw the line. For instance, with emulate_shell=True, what would you do with all the sh/bash built-ins:

https://www.gnu.org/software/bash/manual/html_node/Bourne-Shell-Builtins.htm... https://www.gnu.org/software/bash/manual/html_node/Bash-Builtins.html

I'm thinking especially of the commands where bash has its own handling of something that could otherwise be found in $PATH, like pwd, time, and echo, but shells can do a lot of other things too.

When do you actually want to execute a shell built-in from Python but without using the shell itself? You give the example of ls/dir, but if that ever comes up in real-world code, I'd toss it out and recommend a cross-platform os.listdir or equivalent. There are plenty of times I've wanted a really quick way to redirect a standard stream from Python, but that isn't part of what you're recommending. Can you give a real-world example that would be improved by this?

I know this was just a side note in your original, but I'd like to hear more about what would make it useful.

No, I cannot. I just thought of a way to keep users from using "shell=True". I *think* they do it after they experience that "del" for instance is not found. They conclude "ah, I need the shell", which is not true. Even putting aside the fact this is pure conjecture, the kind of people who make decisions like this will find a zillion more ways to shoot

On 07.01.2018 22:32, Christian Tismer wrote: themselves in the foot. They don't need a cleaner syntax, they need to learn the basics of programming in a high-level language to understand how it's different from programming in the shell. In particular, why spawning a subprocess for something covered by a library function is a bad idea.

So whatever you come up with, the effect should be that people no longer use the shell. THATs what I want, after bad experience with non-escaped "^" in a regex, that caused some really weird result.

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-- Regards, Ivan