feat: add str, repr and getitem to BasisState (#808)

src/braket/circuits/basis_state.py

@@ -33,6 +33,18 @@ def __iter__(self):
     def __eq__(self, other):
         return self.state == other.state
 
+    def __bool__(self):
+        return any(self.state)
+
+    def __str__(self):
+        return self.as_string
+
+    def __repr__(self):
+        return f'BasisState("{self.as_string}")'
+
+    def __getitem__(self, item):
+        return BasisState(self.state[item])
+
 
 BasisStateInput = Union[int, list[int], str, BasisState]
 

test/unit_tests/braket/circuits/test_basis_state.py

@@ -51,6 +51,58 @@
     ),
 )
 def test_as_props(basis_state_input, size, as_tuple, as_int, as_string):
-    assert BasisState(basis_state_input, size).as_tuple == as_tuple
-    assert BasisState(basis_state_input, size).as_int == as_int
-    assert BasisState(basis_state_input, size).as_string == as_string
+    basis_state = BasisState(basis_state_input, size)
+    assert basis_state.as_tuple == as_tuple
+    assert basis_state.as_int == as_int
+    assert basis_state.as_string == as_string == str(basis_state)
+    assert repr(basis_state) == f'BasisState("{as_string}")'
+
+
+@pytest.mark.parametrize(
+    "basis_state_input, index, substate_input",
+    (
+        (
+            "1001",
+            slice(None),
+            "1001",
+        ),
+        (
+            "1001",
+            3,
+            "1",
+        ),
+        (
+            "1010",
+            slice(None, None, 2),
+            "11",
+        ),
+        (
+            "1010",
+            slice(1, None, 2),
+            "00",
+        ),
+        (
+            "1010",
+            slice(None, -2),
+            "10",
+        ),
+        (
+            "1010",
+            -1,
+            "0",
+        ),
+    ),
+)
+def test_indexing(basis_state_input, index, substate_input):
+    assert BasisState(basis_state_input)[index] == BasisState(substate_input)
+
+
+def test_bool():
+    assert all(
+        [
+            BasisState("100"),
+            BasisState("111"),
+            BasisState("1"),
+        ]
+    )
+    assert not BasisState("0")