convert pytorch's tensor in Python API (#1172)

* convert pytorch's tensor

* separate tests for convert pytorch tensor

candle-pyo3/py_src/candle/__init__.pyi

@@ -396,6 +396,11 @@ class Tensor:
         Convert the tensor to a new dtype.
         """
         pass
+    def to_torch(self) -> torch.Tensor:
+        """
+        Converts candle's tensor to pytorch's tensor
+        """
+        pass
     def transpose(self, dim1: int, dim2: int) -> Tensor:
         """
         Returns a tensor that is a transposed version of the input, the given dimensions are swapped.

candle-pyo3/src/lib.rs

@@ -211,6 +211,16 @@ enum Indexer {
     IndexSelect(Tensor),
 }
 
+#[derive(Clone, Debug)]
+struct TorchTensor(PyObject);
+
+impl<'source> pyo3::FromPyObject<'source> for TorchTensor {
+    fn extract(ob: &'source PyAny) -> PyResult<Self> {
+        let numpy_value: PyObject = ob.getattr("numpy")?.call0()?.extract()?;
+        Ok(TorchTensor(numpy_value))
+    }
+}
+
 #[pymethods]
 impl PyTensor {
     #[new]
@@ -246,6 +256,8 @@ impl PyTensor {
             Tensor::new(vs, &Cpu).map_err(wrap_err)?
         } else if let Ok(vs) = data.extract::<Vec<Vec<Vec<f32>>>>(py) {
             Tensor::new(vs, &Cpu).map_err(wrap_err)?
+        } else if let Ok(TorchTensor(numpy)) = data.extract::<TorchTensor>(py) {
+            return PyTensor::new(py, numpy);
         } else {
             let ty = data.as_ref(py).get_type();
             Err(PyTypeError::new_err(format!(
@@ -299,6 +311,18 @@ impl PyTensor {
         M(py).map(self)
     }
 
+    /// Converts candle's tensor to pytorch's tensor
+    /// &RETURNS&: torch.Tensor
+    fn to_torch(&self, py: Python<'_>) -> PyResult<PyObject> {
+        let candle_values = self.values(py)?;
+        let torch_tensor: PyObject = py
+            .import("torch")?
+            .getattr("tensor")?
+            .call1((candle_values,))?
+            .extract()?;
+        Ok(torch_tensor)
+    }
+
     #[getter]
     /// Gets the tensor's shape.
     /// &RETURNS&: Tuple[int]

candle-pyo3/test_pytorch.py

@@ -0,0 +1,14 @@
+import candle
+import torch
+
+# convert from candle tensor to torch tensor
+t = candle.randn((3, 512, 512))
+torch_tensor = t.to_torch()
+print(torch_tensor)
+print(type(torch_tensor))
+
+# convert from torch tensor to candle tensor
+t = torch.randn((3, 512, 512))
+candle_tensor = candle.Tensor(t)
+print(candle_tensor)
+print(type(candle_tensor))