From 4c3e4e2ef9e237ae74cdd68d6a93b3b7f86f3d57 Mon Sep 17 00:00:00 2001
From: Patrice Neff <mail@patrice.ch>
Date: Wed, 28 Oct 2020 12:23:18 +0000
Subject: [PATCH] Fix `VIRTUALENV_PYTHON` environment lookup

The previous change which introduced the fallback discovery (#1995)
broke this behaviour.
---
 src/virtualenv/discovery/builtin.py | 1 +
 tests/unit/config/test_env_var.py   | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/src/virtualenv/discovery/builtin.py b/src/virtualenv/discovery/builtin.py
index 93e2c7bd5..b66ecb193 100644
--- a/src/virtualenv/discovery/builtin.py
+++ b/src/virtualenv/discovery/builtin.py
@@ -25,6 +25,7 @@ def add_parser_arguments(cls, parser):
             "--python",
             dest="python",
             metavar="py",
+            type=str,
             action="append",
             default=[],
             help="interpreter based on what to create environment (path/identifier) "
diff --git a/tests/unit/config/test_env_var.py b/tests/unit/config/test_env_var.py
index 8eb858d7c..8adf955d1 100644
--- a/tests/unit/config/test_env_var.py
+++ b/tests/unit/config/test_env_var.py
@@ -4,6 +4,7 @@
 
 import pytest
 
+from virtualenv.config.cli.parser import VirtualEnvOptions
 from virtualenv.config.ini import IniConfig
 from virtualenv.run import session_via_cli
 from virtualenv.util.path import Path
@@ -31,6 +32,13 @@ def test_value_bad(monkeypatch, caplog, empty_conf):
     assert "invalid literal" in caplog.messages[0]
 
 
+def test_python_via_env_var(monkeypatch):
+    options = VirtualEnvOptions()
+    monkeypatch.setenv(str("VIRTUALENV_PYTHON"), str("python3"))
+    session_via_cli(["venv"], options=options)
+    assert options.python == ["python3"]
+
+
 def test_extra_search_dir_via_env_var(tmp_path, monkeypatch):
     monkeypatch.chdir(tmp_path)
     value = "a{}0{}b{}c".format(os.linesep, os.linesep, os.pathsep)