Defer, ensure library is loaded

[Steven D'Aprano]

On Tue, 13 Feb 2018 08:02:38 -0800, Jason wrote:

> I have a variety of scripts that import some large libraries, and rather
> than create a million little scripts with specific imports, I'd like to
> so something like
> 
> psycopg2 = ensure_imported (psycopg2)
> 
> This way, regardless of invocation I can know psycopg2 is loaded, if it
> hasn't already been loaded. If I just do a normal import 95% of the time
> I'll be waiting time with a meaningless import.
> 
> 
> Can I do that somehow?

Jason, I'm afraid I don't understand your question. I don't understand 
what "ensure_imported" is supposed to do, or how it is different from a 
regular import, or where you are supposed to put it.

If you have a "million scripts" that look like this:

# count down from script 1000000 to 1...
import psycopg2
...

# script 999999
import psycopg2
...

# script 999998
import psycopg2
...


etc, how is that different from a million scripts that look like this?

# count down from script 1000000 to 1...
psycopg2 = ensure_imported(psycopg2)
...


Aside from the ensure_imported version being about double as much typing.

Nor do I understand what you mean by having to spend 95% of your time 
waiting for a meaningless import. If the import is "meaningless", that 
could only possibly mean that you aren't using the imported module. So 
the solution to that is to simply *not* import it. You shouldn't start 
off every module by importing a bazillion modules that you don't use. 
Import only what you actually use.

If you explain your problem a little better, we can possibly help you 
solve it.

Oh, one last thing... you cannot write something like this:

    foomodule = ensure_imported(foomodule)

because the interpreter has to evaluate the value of the name "foomodule" 
on the right hand side of the assignment, and since it hasn't been 
imported yet, you will get a NameError. You have to write:

    foomodule = ensure_imported("foomodule")  # note the quotation marks

to have it work.



-- 
Steve