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Programming Python, Second Edition by Mark Lutz

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The sys Module

On to module details. As mentioned earlier, the sys and os modules form the core of much of Python’s system-related toolset. Let’s now take a quick, interactive tour through some of the tools in these two modules, before applying them in bigger examples.

Platforms and Versions

Like most modules, sys includes both informational names and functions that take action. For instance, its attributes give us the name of the underlying operating system the platform code is running on, the largest possible integer on this machine, and the version number of the Python interpreter running our code:

C:\...\PP2E\System>python
>>> import sys
>>> sys.platform, sys.maxint, sys.version
('win32', 2147483647, '1.5.2 (#0, Apr 13 1999, 10:51:12) [MSC 32 bit (Intel)]')
>>>
>>> if sys.platform[:3] == 'win': print 'hello windows'
...
hello windows

If you have code that must act differently on different machines, simply test the sys.platform string as done here; although most of Python is cross-platform, nonportable tools are usually wrapped in if tests like the one here. For instance, we’ll see later that program launch and low-level console interaction tools vary per platform today -- simply test sys.platform to pick the right tool for the machine your script is running on.

The Module Search Path

The sys module also lets us inspect the module search path both interactively and within a Python program. sys.path is a list of strings representing the true search path in a running Python interpreter. ...

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