Fix issue #4972: adds ftplib.FTP context manager protocol

Doc/library/ftplib.rst

@@ -46,6 +46,25 @@ The module defines the following items:
    connection attempt (if is not specified, the global default timeout setting
    will be used).
 
+   :class:`FTP` class supports the :keyword:`with` statement. Here is a sample
+   on how using it:
+
+    >>> from ftplib import FTP
+    >>> with FTP("ftp1.at.proftpd.org") as ftp:
+    ...     ftp.login()
+    ...     ftp.dir()
+    ...
+    '230 Anonymous login ok, restrictions apply.'
+    dr-xr-xr-x   9 ftp      ftp           154 May  6 10:43 .
+    dr-xr-xr-x   9 ftp      ftp           154 May  6 10:43 ..
+    dr-xr-xr-x   5 ftp      ftp          4096 May  6 10:43 CentOS
+    dr-xr-xr-x   3 ftp      ftp            18 Jul 10  2008 Fedora
+    >>>
+
+   .. versionchanged:: 3.2
+      Support for the :keyword:`with` statement was added.
+
+
 .. class:: FTP_TLS(host='', user='', passwd='', acct='', [keyfile[, certfile[, timeout]]])
 
    A :class:`FTP` subclass which adds TLS support to FTP as described in

Doc/whatsnew/3.2.rst

@@ -66,6 +66,9 @@ Some smaller changes made to the core Python language are:
 New, Improved, and Deprecated Modules
 =====================================
 
+* The :class:`ftplib.FTP` class now supports the context manager protocol
+  (Contributed by Tarek Ziadé and Giampaolo Rodolà; :issue:`4972`.)
+
 * The previously deprecated :func:`string.maketrans` function has been
   removed in favor of the static methods, :meth:`bytes.maketrans` and
   :meth:`bytearray.maketrans`.  This change solves the confusion around which

Lib/ftplib.py

@@ -120,6 +120,20 @@ class FTP:
             if user:
                 self.login(user, passwd, acct)
 
+    def __enter__(self):
+        return self
+
+    # Context management protocol: try to quit() if active
+    def __exit__(self, *args):
+        if self.sock is not None:
+            try:
+                self.quit()
+            except (socket.error, EOFError):
+                pass
+            finally:
+                if self.sock is not None:
+                    self.close()
+
     def connect(self, host='', port=0, timeout=-999):
         '''Connect to host.  Arguments are:
          - host: hostname to connect to (string, default previous host)

Lib/test/test_ftplib.py

@@ -10,6 +10,7 @@ import socket
 import io
 import errno
 import os
+import time
 try:
     import ssl
 except ImportError:
@@ -137,6 +138,9 @@ class DummyFTPHandler(asynchat.async_chat):
         # sends back the received string (used by the test suite)
         self.push(arg)
 
+    def cmd_noop(self, arg):
+        self.push('200 noop ok')
+
     def cmd_user(self, arg):
         self.push('331 username ok')
 
@@ -218,6 +222,7 @@ class DummyFTPServer(asyncore.dispatcher, threading.Thread):
         self.active = False
         self.active_lock = threading.Lock()
         self.host, self.port = self.socket.getsockname()[:2]
+        self.handler_instance = None
 
     def start(self):
         assert not self.active
@@ -241,8 +246,7 @@ class DummyFTPServer(asyncore.dispatcher, threading.Thread):
 
     def handle_accept(self):
         conn, addr = self.accept()
-        self.handler = self.handler(conn)
-        self.close()
+        self.handler_instance = self.handler(conn)
 
     def handle_connect(self):
         self.close()
@@ -459,12 +463,12 @@ class TestFTPClass(TestCase):
 
     def test_rename(self):
         self.client.rename('a', 'b')
-        self.server.handler.next_response = '200'
+        self.server.handler_instance.next_response = '200'
         self.assertRaises(ftplib.error_reply, self.client.rename, 'a', 'b')
 
     def test_delete(self):
         self.client.delete('foo')
-        self.server.handler.next_response = '199'
+        self.server.handler_instance.next_response = '199'
         self.assertRaises(ftplib.error_reply, self.client.delete, 'foo')
 
     def test_size(self):
@@ -512,7 +516,7 @@ class TestFTPClass(TestCase):
     def test_storbinary(self):
         f = io.BytesIO(RETR_DATA.encode('ascii'))
         self.client.storbinary('stor', f)
-        self.assertEqual(self.server.handler.last_received_data, RETR_DATA)
+        self.assertEqual(self.server.handler_instance.last_received_data, RETR_DATA)
         # test new callback arg
         flag = []
         f.seek(0)
@@ -524,12 +528,12 @@ class TestFTPClass(TestCase):
         for r in (30, '30'):
             f.seek(0)
             self.client.storbinary('stor', f, rest=r)
-            self.assertEqual(self.server.handler.rest, str(r))
+            self.assertEqual(self.server.handler_instance.rest, str(r))
 
     def test_storlines(self):
         f = io.BytesIO(RETR_DATA.replace('\r\n', '\n').encode('ascii'))
         self.client.storlines('stor', f)
-        self.assertEqual(self.server.handler.last_received_data, RETR_DATA)
+        self.assertEqual(self.server.handler_instance.last_received_data, RETR_DATA)
         # test new callback arg
         flag = []
         f.seek(0)
@@ -548,14 +552,59 @@ class TestFTPClass(TestCase):
     def test_makeport(self):
         self.client.makeport()
         # IPv4 is in use, just make sure send_eprt has not been used
-        self.assertEqual(self.server.handler.last_received_cmd, 'port')
+        self.assertEqual(self.server.handler_instance.last_received_cmd, 'port')
 
     def test_makepasv(self):
         host, port = self.client.makepasv()
         conn = socket.create_connection((host, port), 2)
         conn.close()
         # IPv4 is in use, just make sure send_epsv has not been used
-        self.assertEqual(self.server.handler.last_received_cmd, 'pasv')
+        self.assertEqual(self.server.handler_instance.last_received_cmd, 'pasv')
+
+    def test_with_statement(self):
+        self.client.quit()
+
+        def is_client_connected():
+            if self.client.sock is None:
+                return False
+            try:
+                self.client.sendcmd('noop')
+            except (socket.error, EOFError):
+                return False
+            return True
+
+        # base test
+        with ftplib.FTP(timeout=2) as self.client:
+            self.client.connect(self.server.host, self.server.port)
+            self.client.sendcmd('noop')
+            self.assertTrue(is_client_connected())
+        self.assertEqual(self.server.handler_instance.last_received_cmd, 'quit')
+        self.assertFalse(is_client_connected())
+
+        # QUIT sent inside the with block
+        with ftplib.FTP(timeout=2) as self.client:
+            self.client.connect(self.server.host, self.server.port)
+            self.client.sendcmd('noop')
+            self.client.quit()
+        self.assertEqual(self.server.handler_instance.last_received_cmd, 'quit')
+        self.assertFalse(is_client_connected())
+
+        # force a wrong response code to be sent on QUIT: error_perm
+        # is expected and the connection is supposed to be closed
+        try:
+            with ftplib.FTP(timeout=2) as self.client:
+                self.client.connect(self.server.host, self.server.port)
+                self.client.sendcmd('noop')
+                self.server.handler_instance.next_response = '550 error on quit'
+        except ftplib.error_perm as err:
+            self.assertEqual(str(err), '550 error on quit')
+        else:
+            self.fail('Exception not raised')
+        # needed to give the threaded server some time to set the attribute
+        # which otherwise would still be == 'noop'
+        time.sleep(0.1)
+        self.assertEqual(self.server.handler_instance.last_received_cmd, 'quit')
+        self.assertFalse(is_client_connected())
 
 
 class TestIPv6Environment(TestCase):
@@ -575,13 +624,13 @@ class TestIPv6Environment(TestCase):
 
     def test_makeport(self):
         self.client.makeport()
-        self.assertEqual(self.server.handler.last_received_cmd, 'eprt')
+        self.assertEqual(self.server.handler_instance.last_received_cmd, 'eprt')
 
     def test_makepasv(self):
         host, port = self.client.makepasv()
         conn = socket.create_connection((host, port), 2)
         conn.close()
-        self.assertEqual(self.server.handler.last_received_cmd, 'epsv')
+        self.assertEqual(self.server.handler_instance.last_received_cmd, 'epsv')
 
     def test_transfer(self):
         def retr():

Misc/NEWS

@@ -351,6 +351,9 @@ C-API
 Library
 -------
 
+- Issue #4972: Add support for the context manager protocol to the ftplib.FTP
+  class.
+
 - Issue #8664: In py_compile, create __pycache__ when the compiled path is
   given.