[Lang] User-friendly exception when copying between ti.field (#3442)

Co-authored-by: Taichi Gardener <[email protected]>

python/taichi/lang/field.py

@@ -156,8 +156,11 @@ def copy_from(self, other):
         Args:
             other (Field): The source field.
         """
-        assert isinstance(other, Field)
-        assert len(self.shape) == len(other.shape)
+        if not isinstance(other, Field):
+            raise TypeError('Cannot copy from a non-field object')
+        if self.shape != other.shape:
+            raise ValueError(f"ti.field shape {self.shape} does not match"
+                             f" the source field shape {other.shape}")
         taichi.lang.meta.tensor_to_tensor(self, other)
 
     @python_scope

tests/python/test_field.py

@@ -146,3 +146,35 @@ def test_field_name():
     for i in range(10):
         d.append(ti.field(dtype=ti.f32, shape=(2, 3), name=f'd{i}'))
         assert d[i].name == f'd{i}'
+
+
+@ti.test()
+@pytest.mark.parametrize('shape', field_shapes)
+@pytest.mark.parametrize('dtype', [ti.i32, ti.f32])
+def test_field_copy_from(shape, dtype):
+    x = ti.field(dtype=ti.f32, shape=shape)
+    other = ti.field(dtype=dtype, shape=shape)
+    other.fill(1)
+    x.copy_from(other)
+    convert = lambda arr: arr[0] if len(arr) == 1 else arr
+    assert (convert(x.shape) == shape)
+    assert (x.dtype == ti.f32)
+    assert ((x.to_numpy() == 1).all())
+
+
+@ti.test()
+def test_field_copy_from_with_mismatch_shape():
+    x = ti.field(dtype=ti.f32, shape=(2, 3))
+    for other_shape in [(2, ), (2, 2), (2, 3, 4)]:
+        other = ti.field(dtype=ti.f16, shape=other_shape)
+        with pytest.raises(ValueError):
+            x.copy_from(other)
+
+
+@ti.test()
+def test_field_copy_from_with_non_filed_object():
+    import numpy as np
+    x = ti.field(dtype=ti.f32, shape=(2, 3))
+    other = np.zeros((2, 3))
+    with pytest.raises(TypeError):
+        x.copy_from(other)