Best way to test if a file descriptor is valid?

[Erik Max Francis]

Noah wrote:

> I have a method that is passed an open file descriptor.
> This file descriptor may have been opened from a file or
> from a serial device or whatever. Is there a good way to test if
> the file descriptor is valid and available for read/write?

Why not just use it as you would normally and then just catch and handle
the OSError/IOError that gets raised if it's invalid?

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