use TF's built-in method to get numpy dtype (deepmodeling#1035)

* use TF's built-in method to get numpy dtype

I got a way to get the numpy type from a int. Take an example
```py
>>> tf.dtypes.as_dtype(19).as_numpy_dtype
<class 'numpy.float16'>
```

`PRECISION_MAPPING` is not used any more, as it's actually not a public API.

By the way, it also supports `str`
```py
>>> tf.dtypes.as_dtype("float16")
tf.float16
```

* sadly only `tf.as_dtype` is supported in TF 1.8

deepmd/common.py

@@ -42,12 +42,6 @@
     "float64": tf.float64,
 }
 
-PRECISION_MAPPING: Dict[int, type] = {
-    1: np.float32,
-    2: np.float64,
-    19: np.float16,
-}
-
 
 def gelu(x: tf.Tensor) -> tf.Tensor:
     """Gaussian Error Linear Unit.

deepmd/entrypoints/transfer.py

@@ -2,7 +2,6 @@
 
 from typing import Dict, Optional, Sequence, Tuple
 from deepmd.env import tf
-from deepmd.common import PRECISION_MAPPING
 import re
 import numpy as np
 import logging
@@ -121,8 +120,8 @@ def transform_graph(raw_graph: tf.Graph, old_graph: tf.Graph) -> tf.Graph:
 
         check_dim(raw_graph_node, old_graph_node, node.name)
         tensor_shape = [dim.size for dim in raw_node.tensor_shape.dim]
-        old_graph_dtype = PRECISION_MAPPING[old_node.dtype]
-        raw_graph_dtype = PRECISION_MAPPING[raw_node.dtype]
+        old_graph_dtype = tf.as_dtype(old_node.dtype).as_numpy_dtype
+        raw_graph_dtype = tf.as_dtype(raw_node.dtype).as_numpy_dtype
         log.info(
             f"{node.name} is passed from old graph({old_graph_dtype}) "
             f"to raw graph({raw_graph_dtype})"

deepmd/utils/graph.py

@@ -2,7 +2,6 @@
 import numpy as np
 from typing import Tuple, Dict
 from deepmd.env import tf
-from deepmd.common import PRECISION_MAPPING
 from deepmd.utils.sess import run_sess
 from deepmd.utils.errors import GraphWithoutTensorError
 
@@ -174,7 +173,7 @@ def get_embedding_net_variables_from_graph_def(graph_def : tf.GraphDef) -> Dict:
     embedding_net_nodes = get_embedding_net_nodes_from_graph_def(graph_def)
     for item in embedding_net_nodes:
         node = embedding_net_nodes[item]
-        dtype = PRECISION_MAPPING[node.dtype]
+        dtype = tf.as_dtype(node.dtype).as_numpy_dtype
         tensor_shape = tf.TensorShape(node.tensor_shape).as_list()
         if (len(tensor_shape) != 1) or (tensor_shape[0] != 1):
             tensor_value = np.frombuffer(node.tensor_content)
@@ -262,7 +261,7 @@ def get_fitting_net_variables_from_graph_def(graph_def : tf.GraphDef) -> Dict:
     fitting_net_nodes = get_fitting_net_nodes_from_graph_def(graph_def)
     for item in fitting_net_nodes:
         node = fitting_net_nodes[item]
-        dtype= PRECISION_MAPPING[node.dtype]
+        dtype= tf.as_dtype(node.dtype).as_numpy_dtype
         tensor_shape = tf.TensorShape(node.tensor_shape).as_list()
         if (len(tensor_shape) != 1) or (tensor_shape[0] != 1):
             tensor_value = np.frombuffer(node.tensor_content)