Python scripts don’t run in a vacuum. Depending on platforms and startup procedures, Python programs may have all sorts of enclosing context; information automatically passed in to the program by the operating system when the program starts up. For instance, scripts have access to the following sorts of system-level inputs and interfaces:
os.getcwd
gives access
to the directory from which a script is started, and many file
tools use its value implicitly.
sys.argv
gives access
to words typed on the command line that are used to start the
program and that serve as script inputs.
os.environ
provides an
interface to names assigned in the enclosing shell (or a parent
program) and passed in to the script.
sys.stdin
, stdout
, and stderr
export the three input/output
streams that are at the heart of command-line shell
tools.
Such tools can serve as inputs to scripts, configuration parameters, and so on. In the next few sections, we will explore these context tools—both their Python interfaces and their typical roles.
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