Allow using a custom Python interpreter to run the PEP517 hooks

pep517/wrappers.py

@@ -116,6 +116,7 @@ class Pep517HookCaller(object):
         pyproject.toml.
     backend_path : The backend path, as per PEP 517, from pyproject.toml.
     runner : A callable that invokes the wrapper subprocess.
+    python_executable : The Python executable used to invoke the backend
 
     The 'runner', if provided, must expect the following:
         cmd : a list of strings representing the command and arguments to
@@ -131,6 +132,7 @@ def __init__(
             build_backend,
             backend_path=None,
             runner=None,
+            python_executable=None,
     ):
         if runner is None:
             runner = default_subprocess_runner
@@ -143,6 +145,9 @@ def __init__(
             ]
         self.backend_path = backend_path
         self._subprocess_runner = runner
+        if not python_executable:
+            python_executable = sys.executable
+        self.python_executable = python_executable
 
     @contextmanager
     def subprocess_runner(self, runner):
@@ -262,7 +267,7 @@ def _call_hook(self, hook_name, kwargs):
             # Run the hook in a subprocess
             with _in_proc_script_path() as script:
                 self._subprocess_runner(
-                    [sys.executable, str(script), hook_name, td],
+                    [self.python_executable, str(script), hook_name, td],
                     cwd=self.source_dir,
                     extra_environ=extra_environ
                 )

tests/test_call_hooks.py

@@ -6,12 +6,18 @@
 import pytest
 import toml
 import zipfile
+import sys
 
 from mock import Mock
 
 from pep517.wrappers import Pep517HookCaller, default_subprocess_runner
 from pep517.wrappers import UnsupportedOperation, BackendUnavailable
 
+
+if sys.version_info[0] == 2:
+    FileNotFoundError = IOError
+
+
 SAMPLES_DIR = pjoin(dirname(abspath(__file__)), 'samples')
 BUILDSYS_PKGS = pjoin(SAMPLES_DIR, 'buildsys_pkgs')
 
@@ -131,3 +137,17 @@ def test_runner_replaced_on_exception(monkeypatch):
 
     hooks.get_requires_for_build_wheel()
     runner.assert_called_once()
+
+
+def test_custom_python_executable(monkeypatch, tmpdir):
+    monkeypatch.setenv('PYTHONPATH', BUILDSYS_PKGS)
+
+    runner = Mock(autospec=default_subprocess_runner)
+    hooks = get_hooks('pkg1', runner=runner, python_executable='some-python')
+
+    with hooks.subprocess_runner(runner):
+        with pytest.raises(FileNotFoundError):
+            # output.json is missing because we didn't actually run the hook
+            hooks.get_requires_for_build_wheel()
+        runner.assert_called_once()
+        assert runner.call_args[0][0][0] == 'some-python'