Merge pull request pypa#667 from perillo/improve-venv-support

flit: improve the --python option

flit/__init__.py

@@ -26,6 +26,15 @@ def find_python_executable(python: Optional[str] = None) -> str:
         python = os.environ.get("FLIT_INSTALL_PYTHON")
     if not python:
         return sys.executable
+    if os.path.isdir(python):
+        # Assume it's a virtual environment and look for the environment's
+        # Python executable.  This is the same behavior used by pip.
+        #
+        # Try both Unix and Windows paths in case of odd cases like cygwin.
+        for exe in ("bin/python", "Scripts/python.exe"):
+            py = os.path.join(python, exe)
+            if os.path.exists(py):
+                return os.path.abspath(py)
     if os.path.isabs(python):  # sys.executable is absolute too
         return python
     # get absolute filepath of {python}

tests/test_find_python_executable.py

@@ -1,6 +1,7 @@
-import os
+from os.path import isabs, basename, dirname
 import re
 import sys
+import venv
 
 import pytest
 
@@ -20,7 +21,23 @@ def test_abs():
 
 
 def test_find_in_path():
-    assert os.path.isabs(find_python_executable("python"))
+    assert isabs(find_python_executable("python"))
+
+
+def test_env(tmp_path):
+    path = tmp_path / "venv"
+    venv.create(path)
+
+    executable = find_python_executable(path)
+    assert basename(dirname(dirname(executable))) == "venv"
+
+
+def test_env_abs(tmp_path, monkeypatch):
+    path = tmp_path / "venv"
+    venv.create(path)
+
+    monkeypatch.chdir(tmp_path)
+    assert isabs(find_python_executable("venv"))
 
 
 @pytest.mark.parametrize("bad_python_name", ["pyhton", "ls", "."])