# How do I create a jitclass that takes a list of jitclass objects?

**URL:** <https://numba.discourse.group/t/how-do-i-create-a-jitclass-that-takes-a-list-of-jitclass-objects/366>\
**Category:** Support: How do I do ...?\
**Created:** [November 27, 2020, 6:02pm UTC](https://numba.discourse.group/t/how-do-i-create-a-jitclass-that-takes-a-list-of-jitclass-objects/366 "2020-11-27T18:02:58Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![alanlujan91](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/alanlujan91/32/83_2.png) [@alanlujan91](https://numba.discourse.group/u/alanlujan91)\
**Post date:** [November 27, 2020, 6:02pm UTC](https://numba.discourse.group/t/how-do-i-create-a-jitclass-that-takes-a-list-of-jitclass-objects/366/1 "2020-11-27T18:02:58Z")

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I need a jitclass that takes in a list of jitclass instances

```
import numpy as np
from numba import int64, types
from numba.experimental import jitclass

spec_foo = {"data": int64[:]}

@jitclass(spec_foo)
class Foo(object):
    def __init__ (self, init_data):
        self.data = init_data

# Want to have a list of Foo instances in the Bar class
spec_bar = {"foo_list": types.List(Foo.class_type.instance_type, reflected=True)}

@jitclass(spec_bar)
class Bar(object):
    def __init__ (self, foo_list):
        # This assigns a reference to a list of Foo instances
        self.foo_list = foo_list

x = np.arange(5).astype(np.int64)
# Build a Foo instance
foo = Foo(x)

# Create a Bar instance that holds a list of Foo instance.
bar = Bar([foo])

```

This results in the following error:

```
<string>:3: NumbaPendingDeprecationWarning: 
Encountered the use of a type that is scheduled for deprecation: type 'reflected list' found for argument 'foo_list' of function 'Bar. __init__'.
For more information visit https://numba.pydata.org/numba-doc/latest/reference/deprecation.html#deprecation-of-reflection-for-list-and-set-types
File "test.py", line 20:
class Bar(object):
    def __init__ (self, foo_list):
    ^
C:\Users\alujan\anaconda3\envs\quantmacro\lib\site-packages\numba\core\ir_utils.py:2031: NumbaPendingDeprecationWarning: 
Encountered the use of a type that is scheduled for deprecation: type 'reflected list' found for argument 'foo_list' of function 'ctor'.
For more information visit https://numba.pydata.org/numba-doc/latest/reference/deprecation.html#deprecation-of-reflection-for-list-and-set-types
File "<string>", line 2:
<source missing, REPL/exec in use?>
  warnings.warn(NumbaPendingDeprecationWarning(msg, loc=loc))

```

Any suggestions on how to better do this?

---

<div class="post-metadata">

**Author:** ![EPronovost](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/epronovost/32/63_2.png) [@EPronovost](https://numba.discourse.group/u/EPronovost)\
**Post date:** [November 29, 2020, 6:03pm UTC](https://numba.discourse.group/t/how-do-i-create-a-jitclass-that-takes-a-list-of-jitclass-objects/366/2 "2020-11-29T18:03:04Z")

</div>

The issue comes from the multiple types of lists in numba: [https://numba.pydata.org/numba-doc/dev/reference/pysupported.html#list](https://numba.pydata.org/numba-doc/dev/reference/pysupported.html#list)  
To make things more confusing, there’s also several list types: [https://github.com/numba/numba/blob/master/numba/core/types/containers.py](https://github.com/numba/numba/blob/master/numba/core/types/containers.py)

Note that the code example above works, and raises the warning. The following code example works and doesn’t raise any warnings. Basically, to use `typed.List`, you need `types.ListType` instead of `types.List`.  
This is not unique to `jitclass`… it’s just that normally if you pass a list to a `jit` function it will infer the correct `types.*` given the arguments passed. Jitclass requires you to define your types ahead of time.

```auto
import numpy as np
from numba import int64, types, typed
from numba.experimental import jitclass

spec_foo = {"data": int64[:]}

@jitclass(spec_foo)
class Foo(object):
    def __init__ (self, init_data):
        self.data = init_data

# Want to have a list of Foo instances in the Bar class
# >>> Use ListType instead of List here.
spec_bar = {"foo_list": types.ListType(Foo.class_type.instance_type)}

@jitclass(spec_bar)
class Bar(object):
    def __init__ (self, foo_list):
        # This assigns a reference to a list of Foo instances
        self.foo_list = foo_list

x = np.arange(5).astype(np.int64)
# Build a Foo instance
foo = Foo(x)

# Create a Bar instance that holds a list of Foo instance.
# >>> Pass a typed.List here.
bar = Bar(typed.List([foo]))

```

With Numba 0.52 you can also simplify the definition of `Bar` to

```auto
import numpy as np
from numba import int64, types, typed
from numba.experimental import jitclass
import typing as pt

spec_foo = {"data": int64[:]}

@jitclass(spec_foo)
class Foo(object):
    def __init__ (self, init_data):
        self.data = init_data

@jitclass
class Bar(object):
    # >>> Use new spec syntax. typing.List will be translated to numba.types.ListType.
    foo_list: pt.List[Foo]
        
    def __init__ (self, foo_list):
        # This assigns a reference to a list of Foo instances
        self.foo_list = foo_list

x = np.arange(5).astype(np.int64)
# Build a Foo instance
foo = Foo(x)

# Create a Bar instance that holds a list of Foo instance.
bar = Bar(typed.List([foo]))

```