Make datatype a constant dict

src/qibotn/backends/cutensornet.py

@@ -2,6 +2,18 @@ import numpy as np
 from qibo.backends.numpy import NumpyBackend
 from qibo.config import raise_error
 from qibo.result import CircuitResult
+import cuquantum  # pylint: disable=import-error
+
+CUDA_TYPES = {
+    "complex64": (
+        cuquantum.cudaDataType.CUDA_C_32F,
+        cuquantum.ComputeType.COMPUTE_32F,
+    ),
+    "complex128": (
+        cuquantum.cudaDataType.CUDA_C_64F,
+        cuquantum.ComputeType.COMPUTE_64F,
+    ),
+}
 
 
 class CuTensorNet(NumpyBackend):  # pragma: no cover
@@ -9,7 +21,6 @@ class CuTensorNet(NumpyBackend):  # pragma: no cover
 
     def __init__(self, runcard):
         super().__init__()
-        import cuquantum  # pylint: disable=import-error
         from cuquantum import cutensornet as cutn  # pylint: disable=import-error
 
         if runcard is not None:
@@ -81,16 +92,8 @@ class CuTensorNet(NumpyBackend):  # pragma: no cover
             super().set_precision(precision)
 
     def cuda_type(self, dtype="complex64"):
-        if dtype == "complex128":
+        if dtype in CUDA_TYPES:
-            return (
+            return CUDA_TYPES[dtype]
-                self.cuquantum.cudaDataType.CUDA_C_64F,
-                self.cuquantum.ComputeType.COMPUTE_64F,
-            )
-        elif dtype == "complex64":
-            return (
-                self.cuquantum.cudaDataType.CUDA_C_32F,
-                self.cuquantum.ComputeType.COMPUTE_32F,
-            )
         else:
             raise TypeError("Type can be either complex64 or complex128")