Sorting a ctypes list without grabbing the value

Question

I'm trying to create a reference to a value in a list and then modify that value in a loop. However, I can't seem to figure out how to sort the data without grabbing its contents.value with list comprehension. What I have so far is:

from ctypes import c_long, pointer

class A:
    def __init__(self):
        self.arg1 = c_long(1)
        self.arg2 = c_long(2)
        self.arg3 = c_long(3)

objB = [A() for _ in range(5)]

objC = [pointer(_objB.arg3) for _objB in objB]

for i in range(5):
    objC[0].contents.value = i
    objC = sorted(objC)

which fails. I found a workaround where the loop becomes:

for i in range(5):
    objC[0].contents.value = i
    objC = sorted([_objC.contents.value for _objC in objC])

But this slows the program down and loses the pointer reference to objB. How can I correctly sort the data in objC reference list?

Answer 1

Use the key option to use the value when sorting.

objC = sorted(objC, key=lambda x: x.contents.value)

You may also want to use objC.sort() to sort the list in place, rather than creating a new list.