Access the current list being built

Question

I was working in Python and wondered if there was a to access the current list being built. Here is what I mean:

def foo():
    return 10
def bar(baz):
    return baz * 2
list = [foo(), bar(this_list[0])]

Notice this_list. The output should be 20 because foo returns 10, then is passed to bar which doubles it, getting 20. How could I do this?

https://stackoverflow.com/questions/2638478/recursive-list-comprehension-in-python is similar to what I am asking, except it is list comp. — xilpex, Apr 28 '20 at 22:57
@FishingCode -- `this_list` is the list being made-- something like `self`. — xilpex, Apr 28 '20 at 23:00
I think it has to be two lines `list = [foo()]` then `list.append(bar(list[0]))` — tdelaney, Apr 28 '20 at 23:04
No, it's not possible to access the list being built. What are you trying to achieve? Just avoiding a temporary variable? — Peter Wood, Apr 28 '20 at 23:10
`list` is a bad name for a list. It hides the builtin name `list` which is used for creating lists. — Peter Wood, Apr 28 '20 at 23:27

score 0 · Answer 1 · answered Apr 28 '20 at 23:24

In your example code, you are trying to assign something to the variable list in a way that tries to use the contents of list itself. Yet, you haven't assigned any contents to list before trying to do this assignment, so the computer has no idea what "the contents of list itself" are supposed to be.

One can't reference the value of a variable before one puts a value inside the variable!

To achieve the desired effect, it's cleaner to simply do things step-by-step, in a "boring" way.

def foo():
    return 10
def bar(baz):
    return baz * 2

list = [foo()]
list.append(baz(list[0]))

Or `a = foo(); values = [a, baz(a)]` – Peter Wood Apr 28 '20 at 23:26 — Peter Wood, Apr 28 '20 at 23:26

Access the current list being built

1 Answers1