docs and made retain_graph optional bool

mlx/io/safetensor.cpp

@@ -127,7 +127,7 @@ std::unordered_map<std::string, array> load_safetensor(
 void save_safetensor(
     std::shared_ptr<io::Writer> out_stream,
     std::unordered_map<std::string, array> a,
-    bool retain_graph) {
+    std::optional<bool> retain_graph_) {
   ////////////////////////////////////////////////////////
   // Check file
   if (!out_stream->good() || !out_stream->is_open()) {
@@ -143,7 +143,7 @@ void save_safetensor(
   });
   size_t offset = 0;
   for (auto& [key, arr] : a) {
-    arr.eval(retain_graph);
+    arr.eval(retain_graph_.value_or(arr.is_tracer()));
     if (arr.nbytes() == 0) {
       throw std::invalid_argument(
           "[save_safetensor] cannot serialize an empty array key: " + key);
@@ -174,7 +174,7 @@ void save_safetensor(
 void save_safetensor(
     const std::string& file_,
     std::unordered_map<std::string, array> a,
-    bool retain_graph) {
+    std::optional<bool> retain_graph) {
   // Open and check file
   std::string file = file_;
 

mlx/ops.h

@@ -1068,9 +1068,9 @@ std::unordered_map<std::string, array> load_safetensor(
 void save_safetensor(
     std::shared_ptr<io::Writer> in_stream,
     std::unordered_map<std::string, array>,
-    bool retain_graph = true);
+    std::optional<bool> retain_graph = std::nullopt);
 void save_safetensor(
     const std::string& file,
     std::unordered_map<std::string, array>,
-    bool retain_graph = true);
+    std::optional<bool> retain_graph = std::nullopt);
 } // namespace mlx::core

python/src/load.cpp

@@ -424,7 +424,7 @@ void mlx_savez_helper(
 void mlx_save_safetensor_helper(
     py::object file,
     py::dict d,
-    bool retain_graph) {
+    std::optional<bool> retain_graph) {
   auto arrays_map = d.cast<std::unordered_map<std::string, array>>();
   if (py::isinstance<py::str>(file)) {
     save_safetensor(py::cast<std::string>(file), arrays_map, retain_graph);

python/src/ops.cpp

@@ -2938,14 +2938,14 @@ void init_ops(py::module_& m) {
       R"pbdoc(
         load(file: str, format: Optional[str] = None, /, *, stream: Union[None, Stream, Device] = None) -> Union[array, Dict[str, array]]
 
-        Load array(s) from a binary file in ``.npy`` or ``.npz`` format.
+        Load array(s) from a binary file in ``.npy``, ``.npz``, or ``.safetensors`` format.
 
         Args:
             file (file, str): File in which the array is saved
             format (str, optional): Format of the file. If ``None``, the format
-              is inferred from the file extension. Supported formats: npy, npz, and safetensors. (default: ``None``)
+              is inferred from the file extension. Supported formats: ``npy``, ``npz``, and ``safetensors``. (default: ``None``)
         Returns:
-            result (array, dict): The loaded array if ``.npy`` file or a dict mapping name to array if ``.npz`` file
+            result (array, dict): The loaded array if ``.npy`` file or a dict mapping name to array if ``.npz`` or ``.safetensors`` file
       )pbdoc");
   m.def(
       "save_safetensor",
@@ -2953,18 +2953,20 @@ void init_ops(py::module_& m) {
       "file"_a,
       "d"_a,
       py::pos_only(),
-      "retain_graph"_a = true,
+      "retain_graph"_a = std::nullopt,
       py::kw_only(),
       R"pbdoc(
-        save_safetensor(file: str, d: Dict[str, array], /, retain_graph: bool = True, *)
+        save_safetensor(file: str, d: Dict[str, array], /, retain_graph: Optional[bool] = None, *)
 
         Save array(s) to a binary file in ``.safetensors`` format. 
+        For more information on the format see https://huggingface.co/docs/safetensors/index.
 
         Args:
             file (file, str): File in which the array is saved
             d (Dict[str, array]): The dict mapping name to array to be saved
-            retain_graph(bool): Optional argument to retain graph
+            retain_graph(Optional[bool]): Optional argument to retain graph
-              during array evaluation before saving. Default: True
+              during array evaluation before saving. If not provided the graph
+              is retained if we are during a function transformation. Default: None
       )pbdoc");
   m.def(
       "where",