# Understanding Type Hinting with Python Arrays (Lists)
**URL:** https://forum.makecode.com/t/understanding-type-hinting-with-python-arrays-lists/43109
**Category:** Arcade
**Created:** [April 3, 2026, 6:03pm UTC](https://forum.makecode.com/t/understanding-type-hinting-with-python-arrays-lists/43109 "2026-04-03T18:03:06Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@michaelcaplan](https://forum.makecode.com/u/michaelcaplan)
#### Post date: [April 3, 2026, 6:03pm UTC](https://forum.makecode.com/t/understanding-type-hinting-with-python-arrays-lists/43109/1 "2026-04-03T18:03:06Z")
I believe I understand that when defining an empty array (list), you need to type hint it.
This does not work:
```auto
class test:
def __init__ (self):
self.a = randint(0, 10)
l = []
for i in range(4):
l.append(test())
pass
for value in l:
print(value.a) #Line 12: unknown object type; cannot lookup attribute 'a'
```
This works:
```auto
class test:
def __init__ (self):
self.a = randint(0, 10)
l: List[test] = []
for i in range(4):
l.append(test())
pass
for value in l:
print(value.a)
```
When introducing a typed list in a class, it throws a strange error:
```auto
class pest:
def __init__ (self):
self.l: List[test] = [] #Line 3: ';' expected.
for i in range(4):
self.l.append(test())
pass
class test:
def __init__ (self):
self.a = randint(0, 10)
pest_obj = pest()
for value in pest_obj.l:
print(value.a)
```
Why is that?
If I "seed’ the list with a value on definition, the compiler does not complain:
```auto
class pest:
def __init__ (self):
self.l = [test()]
for i in range(4):
self.l.append(test())
pass
class test:
def __init__ (self):
self.a = randint(0, 10)
pest_obj = pest()
for value in pest_obj.l:
print(value.a)
```
Thanks for the feedback,
Mike
---
### Author:  [@richard](https://forum.makecode.com/u/richard)
#### Post date: [April 3, 2026, 6:15pm UTC](https://forum.makecode.com/t/understanding-type-hinting-with-python-arrays-lists/43109/2 "2026-04-03T18:15:36Z")
ah, this is definitely a makecode bug (or i guess a python feature we never implemented). we don’t currently have support for annotated assignments on class properties
i’ll file an issue for this. unfortunately, i don’t have a workaround for you right now other than the seeding option you demonstrated
---
### Author:  [@michaelcaplan](https://forum.makecode.com/u/michaelcaplan)
#### Post date: [April 4, 2026, 1:14am UTC](https://forum.makecode.com/t/understanding-type-hinting-with-python-arrays-lists/43109/3 "2026-04-04T01:14:05Z")
Thanks Richard!