Hello world

Here is the mandatory first example:

$ python -c "print( 'hello world')"

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\subsection{ Invoking Python}
An interactive session is started by:

\begin{verbatim}
$ python

CTRL-d ends the session. The startup file for the interactive session is specified by the environment variable PYTHONSTARTUP.

Python scripts are invoked by:

$ python fileName.py

If the first line of the script contains the interpreter, it can be invoked by ./fileName.py.

#!/usr/bin/env python
#
# the following lines execute the startup script. They are optional.
#
import os
filename = os.environ.get('PYTHONSTARTUP')
if filename and os.path.isfile(filename):
        execfile(filename)

print( "hello world")