[Python-ideas] lazy use for optional import

[Abe Dillon]

I really think the whole "lazy" idea is misguided. If it's possible for the
interpreter to determine automatically when it needs to force evaluation of
a lazy expression or statement, then why not make *all* expressions and
statements lazy by default? I think it's pretty clear when to force
evaluation: 1) when the result is used in a control flow
statement/expression 2) when the result is output (file, network, or other
I/O)  and 3) evaluate all pending lazy code before releasing the GIL. At
that point, why not make lazy evaluation an implicit feature of the
language, like the garbage collector.

On Wed, Mar 1, 2017 at 8:58 PM, Chris Barker <chris.barker at noaa.gov> wrote:

> Going through machinations to satisfy PEP 8 makes no sense -- it's s style
> *guide* -- that's it.
>
> -CHB
>
>
> On Tue, Feb 28, 2017 at 3:31 PM, Nicolas Cellier <
> contact at nicolas-cellier.net> wrote:
>
>> I have seen some interest into lazy functionality implementation.
>>
>> I wondered if it can be linked with optional import.
>>
>> PEP 8 <http://www.python.org/dev/peps/pep-0008/> authoritatively states:
>>
>> Imports are always put at the top of the file, just after any module
>> comments and docstrings, and before module globals and constants.
>>
>> So, if we want to stick to PEP8 with non mandatory import, we have to
>> catch the import errors, or jail the class or function using extra
>> functionnality.
>>
>> Why not using the potential lazy keyword to have a nice way to deal with
>> it?
>>
>> For example:
>>
>> lazy import pylab as pl  # do nothing for now
>>>
>>> # do stuff
>>>
>>> def plot(*args):
>>>     pl.figure() # Will raise an ImportError at this point
>>>     pl.plot(...)
>>>
>>
>> That way, our library will raise an ImportError only on plot func usage
>> with an explicit traceback : if matplotlib is not installed, we will have
>> the line where it is used for the first time and we will have the name of
>> the faulty library.
>>
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>
>
>
> --
>
> Christopher Barker, Ph.D.
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