generator vs. list comprehension

Question

I have something, when run as a list comprehension, runs fine.

It looks like,

[myClass().Function(things) for things in biggerThing]

Function is a method, and it builds a list. The method itself doesn't return anything, but lists get manipulated within.

Now when I change it to a generator ,

(myClass().Function(things) for things in biggerThing)

It doesn't manipulate the data like I would expect it to. In fact, it doesn't seem to manipulate it at all.

What is the functional difference between a list comprehension and a generator?

Answer 1

Generators are evaluated on the fly, as they are consumed. So if you never iterate over a generator, its elements are never evaluated.

So, if you did:

for _ in (myClass().Function(things) for things in biggerThing):
    pass

Function would run.

---

Now, your intent really isn't clear here.

Instead, consider using map:

map(myClass().Function, biggerThing)  

Note that this will always use the same instance of MyClass

If that's a problem, then do:

for things in BiggerThing:
    myClass().Function(things)