[Python-ideas] 'Injecting' objects as function-local constants

[Alex Light]

On Fri, Jun 17, 2011 at 9:26 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

>

atdef VAR=EXPR [, VAR=EXPR]*



Such a statement would readily cover the speed enhancement,
>
early-binding and shared state use cases for the default argument hack
>

Doing things this way however removes one of the chief benefits of the
inject statement,
the ability to create multiple versions of the same function with different
sets of shared data.

You earlier gave an example similar to this as an example of what the syntax
 under your proposal would look like.

 def example(arg):
   """Record and return arguments seen"""
   atdef cache=set()

   #do something

   cache.add(arg)
   return arg

under proposal 4 (inject as full blown function, usable like any decorator)
it would look like this instead

@inject(cache = set())
def example(arg):
    """Record and return arguments seen"""

    #do something

    cache.add(arg)
    return arg

but what if, later, you decided you needed 10 different 'example' functions
each with its own cache as well
as the ability to make more.

under your proposal we would have to make extensive changes.
turning the code into

def make_example():
    def example(arg):
        """Record and return arguments seen"""

        #do something

        cache.add(arg)
        return arg
    return example

example_list = [make_example() for i in range(10)]

this code is rather difficult to read and it is difficult at first glance to
figure out what is actually happening

under proposal 4 the result would be much simpler. we could just remove the
@inject and put that on in the
list comprehension, like so.

def _example_func(arg):
    """Record and return arguments seen"""

    #do something

    cache.add(arg)
    return arg

example_list = [inject(cache=set())( _example_func) for i in range(10)]
make_example = lambda: inject(cache=set())( _example_func)

this is IMO far easier to read and understand.
Furthermore it gives the added benefit in that you can chose to run
'example' so that it uses
a true global variable, instead of an injected one.

--Alex
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