Open file handles?

[Thomas Bartkus]

This may be more of a Linux question, but I'm doing this from Python. .....

How can I know if anything (I don't care who or what!) is in the middle of
using a particular file?

This comes in context of needing to copy a file BUT only if I can verify
that something else doesn't have an open write handle to that file.  IOW - I
need to decline the operation if something else hasn't finished writing to
the file.

How can I know?
Thomas Bartkus