Close #19734: ignore pip env vars in ensurepip

Doc/library/ensurepip.rst

@@ -117,6 +117,12 @@ Module API
    *verbosity* controls the level of output to :data:`sys.stdout` from the
    bootstrapping operation.
 
+   .. note::
+
+      The bootstrapping process has side effects on both ``sys.path`` and
+      ``os.environ``. Invoking the command line interface in a subprocess
+      instead allows these side effects to be avoided.
+
    .. note::
 
       The bootstrapping process may install additional modules required by

Lib/ensurepip/__init__.py

@@ -43,10 +43,18 @@ def bootstrap(*, root=None, upgrade=False, user=False,
     """
     Bootstrap pip into the current Python installation (or the given root
     directory).
+
+    Note that calling this function will alter both sys.path and os.environ.
     """
     if altinstall and default_pip:
         raise ValueError("Cannot use altinstall and default_pip together")
 
+    # We deliberately ignore all pip environment variables
+    # See http://bugs.python.org/issue19734 for details
+    keys_to_remove = [k for k in os.environ if k.startswith("PIP_")]
+    for k in keys_to_remove:
+        del os.environ[k]
+
     # By default, installing pip and setuptools installs all of the
     # following scripts (X.Y == running Python version):
     #

Lib/test/test_ensurepip.py

@@ -126,6 +126,14 @@ class TestBootstrap(unittest.TestCase):
             ensurepip.bootstrap(altinstall=True, default_pip=True)
         self.run_pip.assert_not_called()
 
+    def test_pip_environment_variables_removed(self):
+        # ensurepip deliberately ignores all pip environment variables
+        # See http://bugs.python.org/issue19734 for details
+        self.os_environ["PIP_THIS_SHOULD_GO_AWAY"] = "test fodder"
+        ensurepip.bootstrap()
+        self.assertNotIn("PIP_THIS_SHOULD_GO_AWAY", self.os_environ)
+
+
 @contextlib.contextmanager
 def fake_pip(version=ensurepip._PIP_VERSION):
     if version is None:

Lib/test/test_venv.py

@@ -294,11 +294,12 @@ class EnsurePipTest(BaseTest):
             # warnings in current versions of Python. Ensure related
             # environment settings don't cause venv to fail.
             envvars["PYTHONWARNINGS"] = "e"
-            # pip doesn't ignore environment variables when running in
-            # isolated mode, and we don't have an active virtualenv here,
-            # we're relying on the native venv support in 3.3+
+            # ensurepip is different enough from a normal pip invocation
+            # that we want to ensure it ignores the normal pip environment
+            # variable settings. We set PIP_NO_INSTALL here specifically
+            # to check that ensurepip (and hence venv) ignores it.
             # See http://bugs.python.org/issue19734 for details
-            del envvars["PIP_REQUIRE_VIRTUALENV"]
+            envvars["PIP_NO_INSTALL"] = "1"
             try:
                 self.run_with_capture(venv.create, self.env_dir, with_pip=True)
             except subprocess.CalledProcessError as exc:
@@ -328,11 +329,6 @@ class EnsurePipTest(BaseTest):
         # installers works (at least in a virtual environment)
         cmd = [envpy, '-Im', 'ensurepip._uninstall']
         with EnvironmentVarGuard() as envvars:
-            # pip doesn't ignore environment variables when running in
-            # isolated mode, and we don't have an active virtualenv here,
-            # we're relying on the native venv support in 3.3+
-            # See http://bugs.python.org/issue19734 for details
-            del envvars["PIP_REQUIRE_VIRTUALENV"]
             p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                                       stderr=subprocess.PIPE)
             out, err = p.communicate()