Print a note after julia.install with non-default julia (#419)

Author: tkf

src/julia/tests/test_tools.py

@@ -5,7 +5,7 @@
 
 import pytest
 
-from julia.tools import julia_py_executable
+from julia.tools import _non_default_julia_warning_message, julia_py_executable
 
 fake_user = "fa9a5150-8e17-11ea-3f8d-ff1e5ae4a251"
 posix_user_sample_path = os.path.join(os.sep, "home", fake_user, ".local", "bin")
@@ -81,3 +81,8 @@ def test_find_julia_py_executable_not_found(monkeypatch):
         julia_py_executable()
 
     assert "``julia-py`` executable is not found" in str(excinfo.value)
+
+
+def test_non_default_julia_warning_message():
+    msg = _non_default_julia_warning_message("julia1.5")
+    assert "Julia(runtime='julia1.5')" in msg

src/julia/tools.py

@@ -41,6 +41,17 @@ def _julia_version(julia):
         return (0, 0, 0)
 
 
+def _non_default_julia_warning_message(julia):
+    # Avoid confusion like
+    # https://github.com/JuliaPy/pyjulia/issues/416
+    return (
+        "PyCall is setup for non-default Julia runtime (executable) `{julia}`.\n"
+        "To use this Julia runtime, PyJulia has to be initialized first by\n"
+        "    from julia import Julia\n"
+        "    Julia(runtime={julia!r})"
+    ).format(julia=julia)
+
+
 def build_pycall(julia="julia", python=sys.executable, **kwargs):
     # Passing `python` to force build (OP="build")
     install(julia=julia, python=python, **kwargs)
@@ -117,6 +128,9 @@ def install(julia="julia", color="auto", python=None, quiet=False):
     if not quiet:
         print("Precompiling PyCall... DONE", file=sys.stderr)
         print("PyCall is installed and built successfully.", file=sys.stderr)
+        if julia != "julia":
+            print(file=sys.stderr)
+            print(_non_default_julia_warning_message(julia), file=sys.stderr)
         sys.stderr.flush()