Best practices with import?

[Just van Rossum]

Peter Hansen wrote:
> 
> Tom Bryan wrote:
> >
> > Alex wrote:
> >
> > > Goodness, without import, python's close to useless.
> >
> > Well, of course.  But where to import?  What's the most common idiom?
> 
> At the top, unless you have a specific need to import in a
> function.
> 
> Possible reasons to import in a function:
> 
>  1. Readability: if the import is needed in only one
>     function and that's very unlikely ever to change,
>     it might be clearer and cleaner to put it there only.
> 
>  2. Startup time: if you don't have the import outside
>     of the function definitions, it will not execute
>     when your module is first imported by another, but
>     only when one of the functions is called.  This
>     delays the overhead of the import (or avoids it
>     if the functions might never be called).
> 
>  3. There is always one more reason than the ones
>     we've thought of until now.

I know one more:

  4. Overhead: if the module imports a lot of modules,
     and there's a good chance only a few will actually
     be used. This is similar to the "Startup time"
     reason, but goes a little further. If a script
     using your module only uses a small subset of the
     functionality it can save quite some time, especially
     if the imports that can be avoided also import a lot
     of modules.

Just