Set PYTHONUNBUFFERED on shell startup.

Fixes: debbugs:18595

* lisp/progmodes/python.el (python-shell-unbuffered): New var.
(python-shell-calculate-process-environment): Use it.

* test/automated/python-tests.el
(python-shell-calculate-process-environment-4)
(python-shell-calculate-process-environment-5): New tests.
(python-shell-make-comint-3): Use file-equal-p.
(python-shell-get-or-create-process-1)
(python-shell-get-or-create-process-2)
(python-shell-get-or-create-process-3): Fix interpreter for
Windows.

4 files changed, 86 insertions, 43 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 0f16eabdc03..e59c3910fd7 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,10 @@
+2014-11-22  Fabián Ezequiel Gallina  <fgallina@gnu.org>
+
+        Set PYTHONUNBUFFERED on shell startup.
+
+        * progmodes/python.el (python-shell-unbuffered): New var.
+        (python-shell-calculate-process-environment): Use it.
+
 2014-11-22  Michael Albinus  <michael.albinus@gmx.de>
 
         * net/tramp.el (tramp-action-password): Clean password on subsequent
diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 5a5a039afc9..4c27136f3b5 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -94,13 +94,13 @@
 ;;       python-shell-interpreter-args
 ;;       "-i C:\\Python27\\Scripts\\ipython-script.py")
 
-;; If you are experiencing missing or delayed output in your shells,
-;; that's likely caused by your Operating System's pipe buffering
-;; (e.g. this is known to happen running CPython 3.3.4 in Windows 7.
+;; Missing or delayed output used to happen due to differences between
+;; Operating Systems' pipe buffering (e.g. CPython 3.3.4 in Windows 7.
 ;; See URL `http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17304').  To
-;; fix this, using CPython's "-u" commandline argument or setting the
-;; "PYTHONUNBUFFERED" environment variable should help: See URL
-;; `https://docs.python.org/3/using/cmdline.html#cmdoption-u'.
+;; avoid this, the `python-shell-unbuffered' defaults to non-nil and
+;; controls whether `python-shell-calculate-process-environment'
+;; should set the "PYTHONUNBUFFERED" environment variable on startup:
+;; See URL `https://docs.python.org/3/using/cmdline.html#cmdoption-u'.
 
 ;; The interaction relies upon having prompts for input (e.g. ">>> "
 ;; and "... " in standard Python shell) and output (e.g. "Out[1]: " in
@@ -1813,6 +1813,14 @@ Restart the Python shell after changing this variable for it to take effect."
   :group 'python
   :safe 'booleanp)
 
+(defcustom python-shell-unbuffered t
+  "Should shell output be unbuffered?.
+When non-nil, this may prevent delayed and missing output in the
+Python shell.  See commentary for details."
+  :type 'boolean
+  :group 'python
+  :safe 'booleanp)
+
 (defcustom python-shell-process-environment nil
   "List of environment variables for Python shell.
 This variable follows the same rules as `process-environment'
@@ -2087,6 +2095,8 @@ uniqueness for different types of configurations."
         (virtualenv (if python-shell-virtualenv-path
                         (directory-file-name python-shell-virtualenv-path)
                       nil)))
+    (when python-shell-unbuffered
+      (setenv "PYTHONUNBUFFERED" "1"))
     (when python-shell-extra-pythonpaths
       (setenv "PYTHONPATH"
               (format "%s%s%s"
diff --git a/test/ChangeLog b/test/ChangeLog
index 4f7f068e796..0da5f99b226 100644
--- a/test/ChangeLog
+++ b/test/ChangeLog
@@ -1,3 +1,14 @@
+2014-11-22  Fabián Ezequiel Gallina  <fgallina@gnu.org>
+
+        * automated/python-tests.el
+        (python-shell-calculate-process-environment-4)
+        (python-shell-calculate-process-environment-5): New tests.
+        (python-shell-make-comint-3): Use file-equal-p.
+        (python-shell-get-or-create-process-1)
+        (python-shell-get-or-create-process-2)
+        (python-shell-get-or-create-process-3): Fix interpreter for
+        Windows (Bug#18595).
+
 2014-11-15  Fabián Ezequiel Gallina  <fgallina@gnu.org>
 
         * automated/python-tests.el (python-indent-dedenters-8): New test
diff --git a/test/automated/python-tests.el b/test/automated/python-tests.el
index f368f995cae..f84ded8cad2 100644
--- a/test/automated/python-tests.el
+++ b/test/automated/python-tests.el
@@ -1872,6 +1872,23 @@ Using `python-shell-interpreter' and
                            python-shell-virtualenv-path
                            path-separator original-path)))))
 
+(ert-deftest python-shell-calculate-process-environment-4 ()
+  "Test `python-shell-unbuffered' modification."
+  (setenv "PYTHONUNBUFFERED")
+  (let* ((process-environment
+          (python-shell-calculate-process-environment)))
+    ;; Defaults to t
+    (should python-shell-unbuffered)
+    (should (string= (getenv "PYTHONUNBUFFERED") "1"))))
+
+(ert-deftest python-shell-calculate-process-environment-5 ()
+  (setenv "PYTHONUNBUFFERED")
+  "Test `python-shell-unbuffered' modification."
+  (let* ((python-shell-unbuffered nil)
+         (process-environment
+          (python-shell-calculate-process-environment)))
+    (should (not (getenv "PYTHONUNBUFFERED")))))
+
 (ert-deftest python-shell-calculate-exec-path-1 ()
   "Test `python-shell-exec-path' modification."
   (let* ((original-exec-path exec-path)
@@ -1961,8 +1978,9 @@ and `python-shell-interpreter-args' in the new shell buffer."
           (should (process-live-p process))
           (with-current-buffer shell-buffer
             (should (eq major-mode 'inferior-python-mode))
-            (should (string= python-shell-interpreter
-                             (executable-find python-tests-shell-interpreter)))
+            (should (file-equal-p
+                     python-shell-interpreter
+                     (executable-find python-tests-shell-interpreter)))
             (should (string= python-shell-interpreter-args "-i"))))
       (kill-buffer shell-buffer))))
 
@@ -2050,12 +2068,11 @@ and `python-shell-interpreter-args' in the new shell buffer."
   (skip-unless (executable-find python-tests-shell-interpreter))
   (python-tests-with-temp-file
    ""
-   (let* ((python-shell-interpreter
-           (executable-find python-tests-shell-interpreter))
+   (let* ((cmd
+           (concat (executable-find python-tests-shell-interpreter) " -i"))
           (use-dialog-box)
           (dedicated-process-name (python-shell-get-process-name t))
-          (dedicated-process
-           (python-shell-get-or-create-process python-shell-interpreter t))
+          (dedicated-process (python-shell-get-or-create-process cmd t))
           (dedicated-shell-buffer (process-buffer dedicated-process)))
      (unwind-protect
          (progn
@@ -2073,12 +2090,11 @@ and `python-shell-interpreter-args' in the new shell buffer."
   (skip-unless (executable-find python-tests-shell-interpreter))
   (python-tests-with-temp-file
    ""
-   (let* ((python-shell-interpreter
-           (executable-find python-tests-shell-interpreter))
+   (let* ((cmd
+           (concat (executable-find python-tests-shell-interpreter) " -i"))
           (use-dialog-box)
           (process-name (python-shell-get-process-name nil))
-          (process
-           (python-shell-get-or-create-process python-shell-interpreter))
+          (process (python-shell-get-or-create-process cmd))
           (shell-buffer (process-buffer process)))
      (unwind-protect
          (progn
@@ -2088,43 +2104,42 @@ and `python-shell-interpreter-args' in the new shell buffer."
            (kill-buffer shell-buffer)
            ;; Check there are no processes for current buffer.
            (should (not (python-shell-get-process))))
-       (ignore-errors (kill-buffer dedicated-shell-buffer))))))
+       (ignore-errors (kill-buffer shell-buffer))))))
 
 (ert-deftest python-shell-get-or-create-process-3 ()
   "Check shell dedicated/global process preference."
   (skip-unless (executable-find python-tests-shell-interpreter))
   (python-tests-with-temp-file
    ""
-   (let* ((python-shell-interpreter
-           (executable-find python-tests-shell-interpreter))
+   (let* ((cmd
+           (concat (executable-find python-tests-shell-interpreter) " -i"))
+          (python-shell-interpreter python-tests-shell-interpreter)
           (use-dialog-box)
           (dedicated-process-name (python-shell-get-process-name t))
           (global-process)
           (dedicated-process))
-     (unwind-protect
-         (progn
-           ;; Create global process
-           (run-python python-shell-interpreter nil)
-           (setq global-process (get-buffer-process "*Python*"))
-           (should global-process)
-           (set-process-query-on-exit-flag global-process nil)
-           ;; Create dedicated process
-           (run-python python-shell-interpreter t)
-           (setq dedicated-process (get-process dedicated-process-name))
-           (should dedicated-process)
-           (set-process-query-on-exit-flag dedicated-process nil)
-           ;; Prefer dedicated.
-           (should (equal (python-shell-get-or-create-process)
-                          dedicated-process))
-           ;; Kill the dedicated so the global takes over.
-           (kill-buffer (process-buffer dedicated-process))
-           ;; Detect global.
-           (should (equal (python-shell-get-or-create-process) global-process))
-           ;; Kill the global.
-           (kill-buffer (process-buffer global-process))
-           ;; Check there are no processes for current buffer.
-           (should (not (python-shell-get-process))))
-       (ignore-errors (kill-buffer dedicated-shell-buffer))))))
+     (progn
+       ;; Create global process
+       (run-python cmd nil)
+       (setq global-process (get-buffer-process "*Python*"))
+       (should global-process)
+       (set-process-query-on-exit-flag global-process nil)
+       ;; Create dedicated process
+       (run-python cmd t)
+       (setq dedicated-process (get-process dedicated-process-name))
+       (should dedicated-process)
+       (set-process-query-on-exit-flag dedicated-process nil)
+       ;; Prefer dedicated.
+       (should (equal (python-shell-get-or-create-process)
+                      dedicated-process))
+       ;; Kill the dedicated so the global takes over.
+       (kill-buffer (process-buffer dedicated-process))
+       ;; Detect global.
+       (should (equal (python-shell-get-or-create-process) global-process))
+       ;; Kill the global.
+       (kill-buffer (process-buffer global-process))
+       ;; Check there are no processes for current buffer.
+       (should (not (python-shell-get-process)))))))
 
 (ert-deftest python-shell-internal-get-or-create-process-1 ()
   "Check internal shell process creation fallback."