Boxing and unboxing class variable

I’m having an issue with boxing and unboxing a custom class that I’ve extended for numba. The trouble lies with having a class variable that is not passed as a constructor parameter, but is instead inferred from the other constructor parameters. In this case: self._id = self._source + ':' + self._target. Here is the code:

class Edge:
    available_labels = []
    def __init__(self, source, target):
        self._source = source
        self._target = target
        self._id = source + ':' + target
    def get_labels(self):
        return Edge.available_labels

    def __str__(self):
        return self._id

    def __hash__(self):
        return hash(str(self))

    def get_source(self):
        return self._source

    def get_target(self):
        return self._target

    def get_id(self):
        return self._id

    def get_type(self):
        return 'edge'
    def __eq__(self, edge):
        result = False
        if isinstance(self, type(edge)):
            result = self is edge

            result = result or (self._source == edge.get_source() and self._target == edge.get_target())

        return result

import operator
from numba import types
from numba.extending import typeof_impl
from numba.extending import type_callable
from numba.extending import models, register_model
from numba.extending import make_attribute_wrapper
from numba.extending import overload_method, overload
from numba.extending import lower_builtin
from numba.core import cgutils
from numba.extending import unbox, NativeValue, box

# Create new numba type
class EdgeType(types.Type):
    def __init__(self):
        super(EdgeType, self).__init__(name='Edge')

edge_type = EdgeType()

# Type inference
def typeof_edge(val, c):
    return edge_type

# Construct object from Numba functions
def type_edge(context):
    def typer(source, target):
        if isinstance(source, types.UnicodeType) and isinstance(target, types.UnicodeType):
            return edge_type
    return typer

# Define native representation: datamodel
class EdgeModel(models.StructModel):
    def __init__(self, dmm, fe_type):
        members = [
            ('source', types.string),
            ('target', types.string),
            ('id', types.string)
        models.StructModel.__init__(self, dmm, fe_type, members)

# Expose datamodel attributes
make_attribute_wrapper(EdgeType, 'source', 'source')
make_attribute_wrapper(EdgeType, 'target', 'target')
make_attribute_wrapper(EdgeType, 'id', 'id')

# Implement constructor
@lower_builtin(Edge, types.string, types.string)
def impl_edge(context, builder, sig, args):
    typ = sig.return_type
    source, target = args
    edge = cgutils.create_struct_proxy(typ)(context, builder)
    edge.source = source = target
    # = source + ':' + target
    return edge._getvalue()

# Expose properties
@overload_method(EdgeType, "get_id")
def get_id(edge):
    def getter(edge):
    return getter

def edge_eq(edge_1, edge_2):
    if isinstance(edge_1, EdgeType) and isinstance(edge_2, EdgeType):
        def impl(edge_1, edge_2):
            if edge_1.source == edge_2.source and ==
                return True
                return False 
        return impl

def edge_hash(edge):
    def impl(edge):
        return hash(
    return impl

# Tell numba how to make native
def unbox_edge(typ, obj, c):
    source_obj = c.pyapi.object_getattr_string(obj, "_source")
    target_obj = c.pyapi.object_getattr_string(obj, "_target")
    id_obj = c.pyapi.object_getattr_string(obj, "_id")
    edge = cgutils.create_struct_proxy(typ)(c.context, c.builder)
    edge.source = c.unbox(types.string, source_obj).value = c.unbox(types.string, target_obj).value = c.unbox(types.string, id_obj).value
    is_error = cgutils.is_not_null(c.builder, c.pyapi.err_occurred())
    return NativeValue(edge._getvalue(), is_error=is_error)

def box_edge(typ, val, c):
    edge = cgutils.create_struct_proxy(typ)(c.context, c.builder, value=val)
    class_obj = c.pyapi.unserialize(c.pyapi.serialize_object(Edge))
    source_obj =, edge.source)
    target_obj =,
    id_obj =,
    res = c.pyapi.call_function_objargs(class_obj, (source_obj, target_obj, id_obj))
    return res

import numba
def f(n):
    a = Edge('abc', 'a')
    return n

print(f(Edge('abc', 'a')))

The error I’m getting is:

Traceback (most recent call last):
  File "", line 168, in <module>
    print(f(Edge('abc', 'a')))
TypeError: __init__() takes 3 positional arguments but 4 were given

I don’t know the answer, but am curious what you need that’s not in structref.

I assume this is for learning or a simplified example but just throwing it out there. :slight_smile:

The error is coming from:

   res = c.pyapi.call_function_objargs(class_obj, (source_obj, target_obj, id_obj))

in the boxer. It is equivalent to calling Edge(source_obj, target_obj, id_obj) but Edge.__init__ does not take the id. There are to ways to deal with this:

  1. Change __init__ or make a new classmethod for Edge that construct an Edge instance with all 3 attributes.

  2. If you can’t change the definition Edge, you can make the boxer do the equivalent of:

    def make(source, target, id):
        bare_obj = object.__new__(Edge)
        bare_obj._source = source
        bare_obj._target = target
        bare_obj._id = id
        return bare_obj
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