[Python-ideas] Python hook just before NameError

Nick Coghlan ncoghlan at gmail.com
Mon Dec 29 13:46:00 CET 2014

On 29 December 2014 at 21:50, Chris Angelico <rosuav at gmail.com> wrote:

> On Mon, Dec 29, 2014 at 10:43 PM, Nathaniel Smith <njs at pobox.com> wrote:
> > I just set up a PYTHONSTARTUP script to pre-import the obvious things and
> > that fixed this problem for me. You'd still have to make a startup
> script to
> > set up the hook, and it's not like 'import os, sys' will appreciably
> affect
> > startup time.
> Maybe those two won't, but I work with a number of Python students who
> are using heavier libraries like psycopg2 and numpy, so I'd really
> rather not auto-import those into everything. On the other hand, the
> course is currently written for Python 2.7, so I can't actually make
> use of this there... yet. Another reason to nudge the course writers
> about updating to 3.x!

FWIW, making it easier to create CPython variants that pre-populate
__main__ differently (ala pyp or the --pylab option to ipython) is one of
the reasons I'd like to eventually implement the interpreter initialisation
changes proposed in PEP 432 (or see it implemented).

However, even today, it's not particularly difficult to create custom
launch scripts that initialise __main__ with a few different modules based
on what you plan to work on and then set os.environ["PYTHONINSPECT"] = "1"
to drop into the interactive interpreter:

$ python3 -c "import sys, os; os.environ['PYTHONINSPECT'] = '1'"
>>> sys, os
(<module 'sys' (built-in)>, <module 'os' from '/usr/lib64/python3.4/os.py'>)

Making existing pre-initialisation mechanisms easier to discover and/or use
seems like a better path forward than adding yet more tools that are even
more cryptic and hard to follow.


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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