Python：从lambda闭包列表中删除

Question

I have confused myself up to the point I need help:

Suppose I have a list of closures to be executed. Upon execution of such a closure, if a certain condition is met I want it to remove itself from the list. Consider the following:

my_lambdas = []

def some_condition_is_met(n): return n > 5

def my_function(n):
    if some_condition_is_met(n):
        # Remove me from my_lambdas, but how?
        return False
    print(n)
    return True

def make_me_a_lambda(n):
    # Alternatively do removal based on the return value:
    return lambda: my_function(n) or remove_me_but_how() 

my_lambdas.append(make_me_a_lambda(1))
my_lambdas.append(make_me_a_lambda(7))

for l in my_lambdas: l()

In reality I don't have control over the execution the lambdas myself, so I can't say something like:

my_lambdas = [l for l in my_lambdas if l()]

Although I guess it would be possible to wrap the execution of the lambdas in a function I do have control over and pass only that single wrapper function to the host application, if possible I'd like to avoid that additional indirection.

Any help is much appreciated, thanks!

Answer 1

Could you structure it like so:

delenda = []
for l in my_lambdas:
   if not l(): delenda.append(l)
for item in in delenda:
   my_lambdas.remove(item)

And just use the truthiness of the return value to remove the items at execution time?

Alternatively, could you pass callable class instances that knew how to delete themselves from a registry?

from functools import partial

class Deleteme (object):
    REGISTRY = []
    def __init__(self, func, *args):
        self.callable = partial(func, *args)

    def register(self):
        if not self in self.REGISTRY: self.REGISTRY.append(self)

    def __call__(self):
        retval = self.callable()
        if not retval and self in self.REGISTRY:
            self.REGISTRY.remove(self)
        return retval

    @classmethod
    def run_lambdas(cls):
        for lmb in [i for i in cls.REGISTRY] :
            yield lmb()


test1 = Deleteme (lambda q: q > 5, 3)
test2 = Deleteme (lambda q: q > 5, 6)
test3 = Deleteme (lambda q: q > 5, -1)
test1.register()
test2.register()
test3.register()

for item in Deleteme.run_lambdas():
    print item

print Deleteme.REGISTRY
>False
>True
>False
>[<__main__.Deleteme object at 0x00000000026A0048>]  #note only one left in the list

The your 'my_lambdas' will be Deletem.REGISTRY (if ypu want to be tidy you should probably wrap that in a function - asking outside classes to read and write to shared fields directly is Bad Practice, but I'm lazy :) 'run_lambdas' would do the loop-and-remove.

USER ADVISORY - code tested by running exactly once :)