sys.argv is different when in interactive mode in Ipython

Question

When I run a script with Ipython in interactive mode, the sys.argv argument list is different in the interactive part of the execution than in the script.

Is this a bug, or am I doing something wrong?

Thanks!

oskar@RR06:~$ cat test.py
import sys
print(sys.argv)
temp = sys.argv

oskar@RR06:~$ ipython -i test.py -- foo bar
Python 2.7.6 (default, Jun 22 2015, 17:58:13) 
Type "copyright", "credits" or "license" for more information.

IPython 4.2.1 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.
['/home/oskar/test.py', 'foo', 'bar']

In [1]: temp
Out[1]: ['/home/oskar/test.py', 'foo', 'bar']

In [2]: sys.argv
Out[2]: ['/usr/local/bin/ipython', '-i', 'test.py', '--', 'foo', 'bar']

Answer 1

If I just invoke ipython, and look at sys.argv I get

In [3]: sys.argv
Out[3]: ['/usr/bin/ipython3']

Your Out[2] looks the same - the full list as provided by the shell and Python interpreter. Remember we are running a Python session with ipython import:

#!/usr/bin/env python3
# This script was automatically generated by setup.py
if __name__ == '__main__':
    from IPython import start_ipython
    start_ipython()
/usr/bin/ipython3 (END)

But look at ipython -h; in the first paragraph:

it executes the file and exits, passing the remaining arguments to the script, just as if you had specified the same command with python. You may need to specify -- before args to be passed to the script, to prevent IPython from attempting to parse them.

So it's explicitly saying that

ipython -i test.py -- foo bar

becomes (in effect) - or is run as:

python test.py foo bar

The ipython code has a parser (as subclass argparse) that handles many different arguments. But ones it can't handle, or follow -- are set aside, and put in the sys.argv that your test.py sees.

But apparently that sys.argv is not what is given to the interactive session.

I think you'd get the same effect

$ipython
In[0]: %run test.py foo bar
...

%run saves the current sys.argv, and constructs a new one with sys.argv = [filename] + args. Then after running your test.py it restores the sys.argv.

This is not a bug, and you aren't doing anything wrong - except expecting the two sys.argv to be the same. It appears that in a plain Python shell, the two sys.argv are the same (without any of the options that the shell itself uses).