Detect if Python3 is installed before launching PythonPort Genserver

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/service/python_port.ex

@@ -5,15 +5,23 @@ defmodule Mobilizon.PythonPort do
 
   use Export.Python
 
+  @python_path "/usr/bin/python3"
+
+  @doc """
+  Whether Python3 is installed
+  """
+  @spec python_exists? :: boolean
+  def python_exists? do
+    File.exists?(python_path())
+  end
+
   @doc """
   ## Parameters
     - path: directory to include in python path
   """
   @spec python_instance(String.t()) :: pid
   def python_instance(path) do
-    python = "/usr/bin/python3"
-
-    {:ok, pid} = Python.start(python: python, python_path: path)
+    {:ok, pid} = Python.start(python: python_path(), python_path: path)
 
     pid
   end
@@ -25,4 +33,12 @@ defmodule Mobilizon.PythonPort do
   def call_python(pid, module, function, arguments \\ []) do
     Python.call(pid, module, function, arguments)
   end
+
+  @spec python_path :: String.t()
+  defp python_path do
+    case get_in(Application.get_env(:mobilizon, __MODULE__), [:path]) do
+      path when is_binary(path) -> path
+      nil -> @python_path
+    end
+  end
 end