PyCallChainRules

While Julia is great, there are still a lot of existing useful differentiable python code in PyTorch, Jax, etc. Given PyCall.jl is already so great and seamless, one might wonder what it takes to differentiate through those pycalls. This library aims for that ideal.

Thanks to @pabloferz, this works on both CPU and GPU without any array copies via DLPack.jl.

Basic Usage

PyTorch

CPU only

Install Python dependencies

using PyCall
run(`$(PyCall.pyprogramname) -m pip install torch==1.11.0+cpu -f https://download.pytorch.org/whl/cpu/torch_stable.html functorch`)

Example

using PyCallChainRules.Torch: TorchModuleWrapper, torch
using Zygote

indim = 32
outdim = 16
torch_module = torch.nn.Linear(indim, outdim) # Can be anything subclassing torch.nn.Module
jlwrap = TorchModuleWrapper(torch_module)

batchsize = 64
input = randn(Float32, indim, batchsize)
output = jlwrap(input)

target = randn(Float32, outdim, batchsize)
loss(m, x, y) = sum(m(x) .- target)
grad, = Zygote.gradient(m->loss(m, input, target), jlwrap)

GPU

Install Python dependencies

using PyCall
# For CUDA 11 and PyTorch 1.11
run(`$(PyCall.pyprogramname) -m pip install torch==1.11.0+cu113 -f https://download.pytorch.org/whl/cu113/torch_stable.html functorch`)

Example

using CUDA
using PyCallChainRules.Torch: TorchModuleWrapper, torch
using Zygote

@assert CUDA.functional()

indim = 32
outdim = 16
torch_module = torch.nn.Linear(indim, outdim).to(device=torch.device("cuda:0")) # Can be anything subclassing torch.nn.Module
jlwrap = TorchModuleWrapper(torch_module)

batchsize = 64
input = CUDA.cu(randn(Float32, indim, batchsize))
output = jlwrap(input)

target = CUDA.cu(randn(Float32, outdim, batchsize))
loss(m, x, y) = sum(m(x) .- y)
grad, = Zygote.gradient(m->loss(m, input, target), jlwrap)

Jax

CPU only

Install Python dependencies

using PyCall
run(`$(PyCall.pyprogramname) -m pip install jax\["cpu"\]`) # for cpu version

Example

using PyCallChainRules.Jax: JaxFunctionWrapper, jax, stax, pyto_dlpack

batchsize = 64
indim = 32
outdim = 16

init_lin, apply_lin = stax.Dense(outdim)
_, params = init_lin(jax.random.PRNGKey(0), (-1, indim))
params_jl = map(x->DLPack.wrap(x, pyto_dlpack), params)
jlwrap = JaxFunctionWrapper(jax.jit(apply_lin))
input = randn(Float32, indim, batchsize)
output = jlwrap(params_jl, input)

target = randn(Float32, outdim, batchsize)
loss(p, x, y) = sum(jlwrap(p, x) .- y)
grad, = Zygote.gradient(p->loss(p, input, target), params_jl)

GPU

Install Python dependencies

using PyCall
run(`$(PyCall.pyprogramname) -m pip install jax\["cuda"\] -f https://storage.googleapis.com/jax-releases/jax_releases.html`)

Example

using PyCallChainRules.Jax: JaxFunctionWrapper, jax, stax
using CUDA

using PyCallChainRules.Jax: JaxFunctionWrapper, jax, stax, pyto_dlpack

batchsize = 64
indim = 32
outdim = 16

init_lin, apply_lin = stax.Dense(outdim)
_, params = init_lin(jax.random.PRNGKey(0), (-1, indim))
params_jl = map(x->DLPack.wrap(x, pyto_dlpack), params)
jlwrap = JaxFunctionWrapper(jax.jit(apply_lin))
input = CUDA.cu(randn(Float32, indim, batchsize))
output = jlwrap(params_jl, input)

target = CUDA.cu(randn(Float32, outdim, batchsize))
loss(p, x, y) = sum(jlwrap(p, x) .- y)
grad, = Zygote.gradient(p->loss(p, input, target), params_jl)

When mixing jax and julia it's recommended to disable jax's preallocation with setting the environment variable XLA_PYTHON_CLIENT_PREALLOCATE=false.

Current Limitations

• Input and output types of wrapped python functions can only be python tensors or [nested] tuples of python tensors.
• Keyword arguments should not be arrays and do not support differentiation.