...`system()`.
  An interface for this function already exists in the standard module `os` - it was chosen as a simple and straightfoward example.

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...borrow
  The metaphor of ``borrowing'' a reference is not completely correct: the owner still has a copy of the reference.

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...completely.
  Checking that the reference count is at least 1 does not work - the reference count itself could be in freed memory and may thus be reused for another object!

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...tuple.
  These guarantees don't hold when you use the ``old'' style calling convention - this is still found in much existing code.

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...directory.
  Check the manual page of the `dl` package for details.

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