[Python-Dev] PEP397 no command line options to python? (original) (raw)

Vinay Sajip vinay_sajip at yahoo.co.uk
Tue Oct 18 09:10:17 CEST 2011

From a desire to keep the launcher as simple as possible, and to minimise

the

need to synchronise the launcher with command line parameter changes in future versions of Python. As simple as possible yes... but no simpler.  I think having pylauncher behave so differently in the two cases of : py -u test.py py test.py Is very unexpected. And to do so silently, without warning will cause

It's only unexpected if you don't read the PEP. From there:

"The launcher may offer some conveniences for Python developers working interactively - for example, starting the launcher with no command-line arguments will launch the default Python with no command-line arguments. Further, command-line arguments will be supported to allow a specific Python version to be launched interactively - however, these conveniences must not detract from the primary purpose of launching scripts and must be easy to avoid if desired."

real headaches for users, especially since py -h lists -u as one of the options, it does not say 'here are the python options but you must call PythonXX/python.exe to use them'.

Well, it's easy enough to make that clearer in the help output of py.exe :-)  

[headaches : it did for me as I ended up with a broken build of my app due to different parts of my app built for different pythons.]

Why does the need arise to invoke py.exe in a build system? Why not just reference the Python executable you want directly?

To fix this the launcher doesn't need to track all python command line options, only those that take two args.  I don't really see that it will be such a maintenance burden to have the launcher track any new ones.  Python has only two such options after 20 years of development.

As for complexity it's less than 10 lines of C.

Plus tests, presumably ... let's see 'em :-)  

That's a cool feature which I'd not really read up on, but that requires a global configuration file change, it's not doable on a per usage basis.

Per usage = interactively, which is more of a "by-the-by" feature for the launcher, the main purpose being to bring shebang-line functionality to Windows.

Regards,

Vinay Sajip

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