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Programming Python, 3rd Edition by Mark Lutz

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Introducing 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 tool set. Let's now take a quick, interactive tour through some of the tools in these two modules before applying them in bigger examples. We'll start with sys, the smaller of the two; remember that to see a full list of all the attributes in sys, you need to pass it to the dir function (or see where we did so earlier in this chapter).

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 on which the platform code is running, the largest possible integer on this machine, and the version number of the Python interpreter running our code:

C:\...\PP3E\System>python
>>> import sys
>>> sys.platform, sys.maxint, sys.version
('win32', 2147483647, '2.4 (#60, Nov 30 2004, 11:49:19) [MSC v.1310 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 today's program launch and low-level console interaction tools vary per platform—simply test sys.platform to pick the right tool for the machine on which your script is running. ...

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