On 26.10.2021 10:54, Marc-Andre Lemburg wrote:
> [...]
> For the object version, the string would have to be compiled
> as well and then executed at the top of the function somehow :-)
>
> I think for the latter, we'd need a more generic concept of
> deferred execution in Python, but even then, you'd not really
> save typing:
>
> def process_files(processor, files=defer os.listdir(DEFAULT_DIR)):
> if deferred(files): files = eval(files)
> ...
>
> The details are more complex than the above, but it demonstrates
> the idea.
>
> Note that eval() would evaluate an already compiled expression
> encapsulated in a deferred object, so it's not slow or dangerous
> to use.
>
> Now, it may not be obvious, but the key advantage of such
> deferred objects is that you can pass them around, i.e. the
> "defer os.listdir(DEFAULT_DIR)" could also be passed in via
> another function.
Here's a better way to write the above pseudo-code, which makes
the intent clearer:
def process_files(processor, files=defer os.listdir(DEFAULT_DIR)):
if isdeferred(files): files = files.eval()
...
isdeferred() would simply check the object for being a deferred
object.
I'm using "eval" for lack of a better word to say "please run
the deferred code now and in this context)". Perhaps a second
keyword could be used to wrap the whole "if isdeferred()..."
dance into something more intuitive.
Here's an old recipe which uses this concept:
https://code.activestate.com/recipes/502206/
BTW: While thinking about defer some more, I came up with this
alternative syntax for your proposal:
def process_files(processor, defer files=os.listdir(DEFAULT_DIR)):
# results in adding the deferred statement at the top of the
# function, if the parameter is not given, i.e.
if files is NotGiven: files = os.listdir(DEFAULT_DIR)
...
This has the advantage of making things a lot more obvious than the
small added ">", which is easy to miss and the main obstacle I see
with your PEP.
That said, I still like the idea to be able to "inject" expressions
into functions. This opens up lots of doors to make dynamic
programming more intuitive in Python.
--
Marc-Andre Lemburg
eGenix.com
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