Question

I usually write python in emacs.

I’ll often want to re-evaluate my file, which I can do with Ctrl-C Ctrl-C, which causes the interpreter to reload the entire file and then I can carry on playing.

so if I’m writing a program that takes input, I’ll usually find myself with two lines:

lines = open("/home/jla/inputfile").readlines()
#lines = fileinput.input()

the first line is ‘what to do while developing’ (read from a known example input file)
the second is ‘what to do when run from the command line’ (read from stdin, or a provided file name)

Obviously this is bad, so I am thinking:

if in_emacs():
     lines = open("/home/jla/inputfile").readlines()
if run_from_shell():
     lines = fileinput.input()
else:
     oops()

And I know how to write oops(), but I am a bit stuck with in_emacs() and run_from_shell(), and I wonder if you wise ones can help.

Answer 1

Shells opened by emacs should have the environment variable EMACS=t. At least this works on my emacs, YMMV.

If that doesn’t fly for you, here’s how to find out what emacs-dependent environment variables python can see. Run from the shell and under emacs, and compare the outputs.

import os
for e in os.environ:
    if 'EMACS' in e:
        print e, os.environ[e]