use env variable

Author: PhilipVinc

PyPreferences.jl/src/core.jl

@@ -84,6 +84,12 @@ function PyPreferences.recompile()
     return
 end
 
+"""
+Returns the default python executable used by PyCall. This defaults to
+`python3`, and can be overridden by `ENV["PYTHON"]` if it is desired.
+"""
+get_default_python() = get(ENV,"PYTHON", "python3")
+
 function get_python_fullpath(python)
     python_fullpath = nothing
     if python !== nothing
@@ -112,12 +118,11 @@ function setup_non_failing()
     inprocess = prefs.inprocess
     conda = prefs.conda
 
-    if !inprocess   
+    if !inprocess 
         if conda
             python = python_fullpath = conda_python_fullpath()
         elseif python === nothing
-            # TODO: mimic PyCall's deps/build.jl
-            python = "python3"
+            python = get_default_python()
         end
 
         @debug "Python binary selected. Attempting to find the path" python