I would use IPython as a scripting language. It has a slow startup time though.
On Thu, Oct 3, 2019 at 9:59 AM Chris Angelico <ros...@gmail.com> wrote: > On Thu, Oct 3, 2019 at 11:41 PM Hongyi Zhao <hongyi.z...@gmail.com> wrote: > > > > On Thu, 03 Oct 2019 23:12:45 +1000, Chris Angelico wrote: > > > > > > > Seems fine. Most of the code is elsewhere, and presumably has been > > > written to support both Py2 and Py3; the file you're linking to is > > > *just* a wrapper that finds an interpreter to use. > > > > > > Though this should be unnecessary. A simple shebang of "/usr/bin/env > > > python3" will suffice for many many situations (and then if someone > > > specifically wants to run it in a legacy interpreter, an explicit > > > "python2 scriptname.py" or "python scriptname.py" will work). > > > > I'm very confusing on the following part in this script: > > > > ---- > > ''':' # begin python string; this line is interpreted by the shell as `:` > > which python >/dev/null 2>&1 && exec python "$0" "$@" > > which python3 >/dev/null 2>&1 && exec python3 "$0" "$@" > > which python2 >/dev/null 2>&1 && exec python2 "$0" "$@" > > >&2 echo "error: cannot find python" > > exit 1 > > ''' > > ---- > > > > Any hints for the meaning of several ' used above? > > > > The hint is there in that line, and stems from the way two different > parsers (Python and sh) interpret the line. In Python, three single > quote characters start a triple-quoted string, which doesn't end till > you get three more; since nothing is done with this string, Python > parses it and then ignores it. In the shell, the first two are an > empty string, then ':' is a colon, which introduces a label (the fact > that it's in quotes is irrelevant to the shell). So there's an empty > label followed by a shell comment. The shell parses this line and does > nothing with it. Then it moves on to the next lines, and runs the > shell script. Since this shell script ends with 'exit 1', it's > guaranteed to halt execution (and usually it'll exec to python, which > also halts execution), so the Python code won't be executed. > > This is a common trick when writing polyglot code. You make the > relevant code for one language appear as a comment or string literal > in another. For instance, you can open a C program with "#if 0", which > will cause the following text to be ignored by the C preprocessor; but > since that line begins with a hash, Python will ignore it (but > continue executing). > > ChrisA > -- > https://mail.python.org/mailman/listinfo/python-list > -- https://mail.python.org/mailman/listinfo/python-list
