Change eval to return nil when code does not end with an expression

Author: jonatanklosko

c_src/pythonx/pythonx.cpp

@@ -1105,7 +1105,7 @@ std::tuple<PyObjectPtr, PyObjectPtr> compile(ErlNifEnv *env,
   return std::make_tuple(py_body_code, py_last_expr_code);
 }
 
-std::tuple<ExObject, fine::Term>
+std::tuple<std::optional<ExObject>, fine::Term>
 eval(ErlNifEnv *env, ErlNifBinary code, std::string code_md5,
      std::vector<std::tuple<ErlNifBinary, ExObject>> globals,
      ErlNifPid stdout_device, ErlNifPid stderr_device) {
@@ -1276,14 +1276,12 @@ eval(ErlNifEnv *env, ErlNifBinary code, std::string code_md5,
     Py_DecRef(py_body_result);
   }
 
-  PyObjectPtr py_result;
+  auto result = std::optional<ExObject>();
 
-  if (py_last_expr_code == nullptr) {
-    py_result = Py_BuildValue("");
-    raise_if_failed(env, py_result);
-  } else {
-    py_result = PyEval_EvalCode(py_last_expr_code, py_globals, py_globals);
+  if (py_last_expr_code != nullptr) {
+    auto py_result = PyEval_EvalCode(py_last_expr_code, py_globals, py_globals);
     raise_if_failed(env, py_result);
+    result = ExObject(fine::make_resource<ExObjectResource>(py_result));
   }
 
   // Step 4: flat-decode globals
@@ -1326,8 +1324,7 @@ eval(ErlNifEnv *env, ErlNifBinary code, std::string code_md5,
     throw std::runtime_error("failed to make a map");
   }
 
-  return std::make_tuple(
-      ExObject(fine::make_resource<ExObjectResource>(py_result)), map);
+  return std::make_tuple(result, map);
 }
 
 FINE_NIF(eval, ERL_NIF_DIRTY_JOB_CPU_BOUND);

lib/pythonx.ex

@@ -108,8 +108,8 @@ defmodule Pythonx do
   by calling `encode!/1`.
 
   The function returns the evaluation result and a map with the updated
-  global variables. Note that, unless `code` ends with an expression,
-  the result will be a `None` object.
+  global variables. Note that the result is an object only if `code`
+  ends with an expression, otherwise it is `nil`.
 
   If the Python code raises an exception, `Pythonx.Error` is raised and
   the message includes the usual Python error message with traceback.
@@ -196,7 +196,7 @@ defmodule Pythonx do
 
   '''
   @spec eval(String.t(), %{optional(String.t()) => term()}) ::
-          {Object.t(), %{optional(String.t()) => Object.t()}}
+          {Object.t() | nil, %{optional(String.t()) => Object.t()}}
   def eval(code, globals) do
     globals =
       for {key, value} <- globals do

test/pythonx_test.exs

@@ -155,7 +155,7 @@ defmodule PythonxTest do
                  %{}
                )
 
-      assert repr(result) == "None"
+      assert result == nil
       assert repr(nums) == "[1, 2, 3]"
       assert repr(sum) == "6"
     end
@@ -174,12 +174,12 @@ defmodule PythonxTest do
       assert repr(result) == "2"
     end
 
-    test "returns none for empty code" do
+    test "returns nil for empty code" do
       assert {result, %{}} = Pythonx.eval("", %{})
-      assert repr(result) == "None"
+      assert result == nil
 
       assert {result, %{}} = Pythonx.eval("# Comment", %{})
-      assert repr(result) == "None"
+      assert result == nil
     end
 
     test "encodes terms given as globals" do