On Monday December 5 2016 11:23, in comp.lang.python, "BartC" <b...@freeuk.com> wrote:
> On 05/12/2016 15:53, Chris Angelico wrote: >> On Tue, Dec 6, 2016 at 2:41 AM, BartC <b...@freeuk.com> wrote: >>> >>> Are you saying that if someone executes: >>> >>> subprocess.Popen(["python","a.py", "*"]) >>> >>> the output will be: ['a.py','*']? >>> >>> In that case forget Windows vs. Linux, you now have a program that will >>> get command parameters processed differently depending on whether it was >>> invoked from a shell or not. >> >> Yes, that is correct. *SHELLS DO STUFF*. If you can't comprehend this, >> you should get to know your shell. Try this: >> >> python a.py %PATH% >> >> subprocess.Popen(["python", "a.py", "%PATH%"]) >> >> Would you expect those to do the same? If you do, prepare for Windows >> to surprise you. If you don't, why do you keep expecting other shells >> to do nothing? > > You still don't get point. I write a program P, a native executable. It > takes command line parameters but exactly what it gets depends on > whether it's started from a 'shell' or from inside another program? In Unix, it always has. > I > don't want to worry about that stuff or exactly how it is invoked! Then, I guess that you have a problem, don't you? > > subprocess.Popen(["python", "a.py", "%PATH%"]) > > Yes, %...% is an escape sequence. Those % signs are supposed to stand > out and have been chosen not to clash with typical input. > > And the end result of the transformation is, here, also a SINGLE thing; > any parameter following will still be the second parameter, not the 14771th! > > Are you saying that the * in ABC*EF also makes the whole thing some > escape pattern? If you ask the shell to parse the arguments, then, "YES, the * in ABC*EF makes the argument a candidate for globbing". > And one that could massively expand the number of parameters, Yes > pushing all the following ones out of the way, and making it > impossible to discover where these expanded parameters end and the > normal ones recommence. The best way to think about it is that all parameters are parameters, whether derived from a glob input to a shell, or explicitly specified in the invocation. If you have a need for positional parameters, then either specify that your code only accepts them in specific places, or find a way to disable globbing (it can be done) and handle the expansion yourself, in your own code. > If someone had thought this up now, it would rapidly be dismissed as > being unworkable. But because it's been in Unix/Linux/whatever so long, > no one can see anything wrong with it! Primarily because there /IS/ nothing wrong with it. -- Lew Pitcher "In Skills, We Trust" PGP public key available upon request -- https://mail.python.org/mailman/listinfo/python-list
