# JuliaCall and SimpleChains not working together

**URL:** <https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978>\
**Category:** General Usage\
**Tags:** python, juliacall\
**Created:** [September 9, 2022, 9:53am UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978 "2022-09-09T09:53:09Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![marcobonici](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marcobonici/32/20549_2.png) [@marcobonici](https://discourse.julialang.org/u/marcobonici)\
**Post date:** [September 9, 2022, 9:53am UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/1 "2022-09-09T09:53:10Z")

</div>

Hi,  
I have been working on a surrogate model, based on SimpleChains NNs, and I am quite satisfied with the performance.

> from juliacall import Main as jl

jl.seval(“using Capse”)  
jl.seval(“using SimpleChains”)

Since I need to deliver the trained surrogate models to python people, I have been trying to build a small python wrapper and I decided to use JuliaCall. It looks very nice, but I am not being able to run SImpleChains from the python interface.

Here I’ll write a small (quick and dirty) MWE just to show my problem

```julia
import numpy as np
from juliacall import Main as jl

jl.seval("using SimpleChains")
mlpd = jl.seval('SimpleChain(static(8), TurboDense(tanh, 64), TurboDense(tanh, 64), TurboDense(tanh, 64), TurboDense(identity, 4))')
p = jl.seval('SimpleChains.init_params(SimpleChain(static(8), TurboDense(tanh, 64), TurboDense(tanh, 64), TurboDense(tanh, 64),TurboDense(identity, 4)))')

```

Now, if I run

```julia
input_test = np.random.rand(8)
mlpd(input_test,p)

```

I get the following error

```julia
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/mbonici/.julia/packages/PythonCall/2Y5CR/src/jlwrap/any.jl", line 201, in __call__
    return self._jl_callmethod($(pyjl_methodnum(pyjlany_call)), args, kwargs)
juliacall.JuliaError: "Memory access for PythonCall.PyArray{Float64, 1, true, true, Float64} not implemented yet."
Stacktrace:
  [1] memory_reference
    @ ~/.julia/packages/LayoutPointers/ssuuk/src/stridedpointers.jl:59 [inlined]
  [2] memory_reference
    @ ~/.julia/packages/LayoutPointers/ssuuk/src/stridedpointers.jl:16 [inlined]
  [3] stridedpointer
    @ ~/.julia/packages/LayoutPointers/ssuuk/src/stridedpointers.jl:93 [inlined]
  [4] PtrArray
    @ ~/.julia/packages/StrideArraysCore/VQxXL/src/ptr_array.jl:33 [inlined]
  [5] TurboDense
    @ ~/.julia/packages/SimpleChains/HhLUa/src/dense.jl:150 [inlined]
  [6] __chain
    @ ~/.julia/packages/SimpleChains/HhLUa/src/simple_chain.jl:286 [inlined]
  [7] _chain
    @ ~/.julia/packages/SimpleChains/HhLUa/src/simple_chain.jl:336 [inlined]
  [8] with_heap_memory(::typeof(SimpleChains._chain), ::SimpleChain{Tuple{StaticInt{8}}, Tuple{TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{2499}, typeof(identity)}}}, ::StaticInt{22623}, ::PythonCall.PyArray{Float64, 1, true, true, Float64}, ::Ptr{Float32})
    @ SimpleChains ~/.julia/packages/SimpleChains/HhLUa/src/memory.jl:36
  [9] (::SimpleChain{Tuple{StaticInt{8}}, Tuple{TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{2499}, typeof(identity)}}})(arg::PythonCall.PyArray{Float64, 1, true, true, Float64}, params::StrideArraysCore.StaticStrideArray{Tuple{StaticInt{179651}}, (true,), Float32, 1, 1, 0, (1,), Tuple{StaticInt{4}}, Tuple{StaticInt{1}}, 179651})
    @ SimpleChains ~/.julia/packages/SimpleChains/HhLUa/src/simple_chain.jl:170
 [10] pyjlany_call(self::SimpleChain{Tuple{StaticInt{8}}, Tuple{TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{64}, typeof(tanh)}, TurboDense{true, StaticInt{2499}, typeof(identity)}}}, args_::PythonCall.Py, kwargs_::PythonCall.Py)
    @ PythonCall ~/.julia/packages/PythonCall/2Y5CR/src/jlwrap/any.jl:31
 [11] _pyjl_callmethod(f::Any, self_::Ptr{PythonCall.C.PyObject}, args_::Ptr{PythonCall.C.PyObject}, nargs::Int64)
    @ PythonCall ~/.julia/packages/PythonCall/2Y5CR/src/jlwrap/base.jl:69
 [12] _pyjl_callmethod(o::Ptr{PythonCall.C.PyObject}, args::Ptr{PythonCall.C.PyObject})
    @ PythonCall.C ~/.julia/packages/PythonCall/2Y5CR/src/cpython/jlwrap.jl:47

```

I have already built a small wrapper using JuliaCall and never found such an error.  
Thank you for your help with this issue.  
(Tagging @ChrisRackauckas @Elrod and @cjdoris )  
Cheers,  
Marco  
Edit: Ialready looked into pywrap/PyArray.jl, after reading the error, but I don’t think I would be able to modify it and/or make a PR.

---

<div class="post-metadata">

**Author:** ![jbrea](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jbrea/32/3879_2.png) [@jbrea](https://discourse.julialang.org/u/jbrea)\
**Post date:** [September 9, 2022, 11:14am UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/2 "2022-09-09T11:14:38Z")

</div>

Would copying be a solution? I ran into a similar issue at some point and solved the problem on the julia side with

```julia
function_to_call_from_python(input, p) = mlpd(copy(input), p)

```

---

<div class="post-metadata">

**Author:** ![marcobonici](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marcobonici/32/20549_2.png) [@marcobonici](https://discourse.julialang.org/u/marcobonici)\
**Post date:** [September 9, 2022, 11:16am UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/3 "2022-09-09T11:16:10Z")

</div>

Now I am having lunch.  
But sure, I’ll try it as soon as I get access to my computer again.  
Thanks for the suggestion!

---

<div class="post-metadata">

**Author:** ![marcobonici](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marcobonici/32/20549_2.png) [@marcobonici](https://discourse.julialang.org/u/marcobonici)\
**Post date:** [September 9, 2022, 12:31pm UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/4 "2022-09-09T12:31:34Z")

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I just tried and it didn’t work 😓 .  
The error message I obtain is

```julia
juliacall.JuliaError: MethodError: no method matching copy(::PythonCall.Py)

```

---

<div class="post-metadata">

**Author:** ![cjdoris](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cjdoris/32/213133_2.png) [@cjdoris](https://discourse.julialang.org/u/cjdoris)\
**Post date:** [September 9, 2022, 12:58pm UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/5 "2022-09-09T12:58:46Z")

</div>

Something like this should work:

```python
import numpy as np
from juliacall import Main as jl

jl.seval("using SimpleChains")
mlpd = jl.seval('SimpleChain(static(8), TurboDense(tanh, 64), TurboDense(tanh, 64), TurboDense(tanh, 64), TurboDense(identity, 4))')
p = jl.SimpleChains.init_params(mlpd)

input_test = np.random.rand(8)
mlpd(jl.collect(input_test), p)

```

What’s going on is that when the numpy array is passed to a Julia function, it is automatically converted to a `PyArray` (which wraps the underlying data as an `AbstractArray`). From the error you posted, it appears that your model requires a strided array as input. Now `PyArray` **is** a strided array, but `ArrayInterface.jl` does not know this, hence the error.

The above code calls `collect` on the `PyArray`, which will convert it to a normal `Array`, which should work in your model.

Alternatively you can convert straight to `Array` (skipping the intermediate `PyArray`) like so:

```python
from juliacall import convert as jlconvert
mlpd(jlconvert(jl.Array, input_test), p)

```

This way is more verbose, but also more explicit about what conversion is happening.

The real solution is for PythonCall to define the right overloads for ArrayInterface so that it knows `PyArray` is strided. There’s an issue for it here: [Use ArrayInterface.jl? · Issue #61 · cjdoris/PythonCall.jl · GitHub](https://github.com/cjdoris/PythonCall.jl/issues/61).

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<div class="post-metadata">

**Author:** ![marcobonici](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marcobonici/32/20549_2.png) [@marcobonici](https://discourse.julialang.org/u/marcobonici)\
**Post date:** [September 9, 2022, 2:11pm UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/6 "2022-09-09T14:11:38Z")

</div>

Thank you!  
I tried what you suggested and it worked…thank you!

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<div class="post-metadata">

**Author:** ![Elrod](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/elrod/32/22461_2.png) [@Elrod](https://discourse.julialang.org/u/Elrod)\
**Post date:** [September 10, 2022, 8:24pm UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/7 "2022-09-10T20:24:03Z")

</div>

Alternatively, it should be possible to support the `ArrayInterface` with a `PyArray`.

---

<div class="post-metadata">

**Author:** ![cjdoris](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cjdoris/32/213133_2.png) [@cjdoris](https://discourse.julialang.org/u/cjdoris)\
**Post date:** [September 10, 2022, 8:47pm UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/8 "2022-09-10T20:47:41Z")

</div>

Yep thanks I noted that at the end of my reply.

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<div class="post-metadata">

**Author:** ![Elrod](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/elrod/32/22461_2.png) [@Elrod](https://discourse.julialang.org/u/Elrod)\
**Post date:** [September 10, 2022, 9:12pm UTC](https://discourse.julialang.org/t/juliacall-and-simplechains-not-working-together/86978/9 "2022-09-10T21:12:28Z")

</div>

Ah, yes, and an issue you made from October 2021. You’re way ahead of me. 😉