Fix #10554. Added context manager support to Popen objects.

Added a few common Popen uses to the tests like we've done for a few other
instances of adding context managers. Eventually the entire test suite
could be converted to use the context manager format.

Doc/library/subprocess.rst

@@ -208,6 +208,16 @@ This module defines one class called :class:`Popen`:
    underlying CreateProcess() function.  They can specify things such as appearance
    of the main window and priority for the new process.  (Windows only)
 
+   Popen objects are supported as context managers via the :keyword:`with` statement,
+   closing any open file descriptors on exit.
+   ::
+
+      with Popen(["ifconfig"], stdout=PIPE) as proc:
+          log.write(proc.stdout.read())
+
+   .. versionchanged:: 3.2
+      Added context manager support.
+
 
 .. data:: PIPE
 

Lib/subprocess.py

@@ -697,6 +697,16 @@ class Popen(object):
         data = data.replace(b"\r\n", b"\n").replace(b"\r", b"\n")
         return data.decode(encoding)
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        if self.stdout:
+            self.stdout.close()
+        if self.stderr:
+            self.stderr.close()
+        if self.stdin:
+            self.stdin.close()
 
     def __del__(self, _maxsize=sys.maxsize, _active=_active):
         if not self._child_created:

Lib/test/test_subprocess.py

@@ -1183,6 +1183,47 @@ class CommandsWithSpaces (BaseTestCase):
         # call() function with sequence argument with spaces on Windows
         self.with_spaces([sys.executable, self.fname, "ab cd"])
 
+
+class ContextManagerTests(ProcessTestCase):
+
+    def test_pipe(self):
+        with subprocess.Popen([sys.executable, "-c",
+                               "import sys;"
+                               "sys.stdout.write('stdout');"
+                               "sys.stderr.write('stderr');"],
+                              stdout=subprocess.PIPE,
+                              stderr=subprocess.PIPE) as proc:
+            self.assertEqual(proc.stdout.read(), b"stdout")
+            self.assertStderrEqual(proc.stderr.read(), b"stderr")
+
+        self.assertTrue(proc.stdout.closed)
+        self.assertTrue(proc.stderr.closed)
+
+    def test_returncode(self):
+        with subprocess.Popen([sys.executable, "-c",
+                               "import sys; sys.exit(100)"]) as proc:
+            proc.wait()
+        self.assertEqual(proc.returncode, 100)
+
+    def test_communicate_stdin(self):
+        with subprocess.Popen([sys.executable, "-c",
+                              "import sys;"
+                              "sys.exit(sys.stdin.read() == 'context')"],
+                             stdin=subprocess.PIPE) as proc:
+            proc.communicate(b"context")
+            self.assertEqual(proc.returncode, 1)
+
+    def test_invalid_args(self):
+        with self.assertRaises(EnvironmentError) as c:
+            with subprocess.Popen(['nonexisting_i_hope'],
+                                  stdout=subprocess.PIPE,
+                                  stderr=subprocess.PIPE) as proc:
+                pass
+
+            if c.exception.errno != errno.ENOENT:  # ignore "no such file"
+                raise c.exception
+
+
 def test_main():
     unit_tests = (ProcessTestCase,
                   POSIXProcessTestCase,
@@ -1191,7 +1232,8 @@ def test_main():
                   CommandTests,
                   ProcessTestCaseNoPoll,
                   HelperFunctionTests,
-                  CommandsWithSpaces)
+                  CommandsWithSpaces,
+                  ContextManagerTests)
 
     support.run_unittest(*unit_tests)
     support.reap_children()

Misc/NEWS

@@ -58,6 +58,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #10554: Add context manager support to subprocess.Popen objects.
+
 - Issue #8989: email.utils.make_msgid now has a domain parameter that can
   override the domain name used in the generated msgid.