gh-73965: New environment variable PYTHON_HISTORY

Doc/using/cmdline.rst

@@ -918,6 +918,14 @@ conflict.
    .. versionadded:: 3.7
       See :pep:`540` for more details.
 
+.. envvar:: PYTHONHISTORY
+
+   This environment variable can be used to set the location of a
+   ``.python_history`` file (by default, it is ``.python_history`` in the
+   user's home directory).
+
+   .. versionadded:: 3.8
+
 
 Debug-mode variables
 ~~~~~~~~~~~~~~~~~~~~

Doc/whatsnew/3.8.rst

@@ -298,6 +298,9 @@ Other Language Changes
 * Added new ``replace()`` method to the code type (:class:`types.CodeType`).
   (Contributed by Victor Stinner in :issue:`37032`.)
 
+* The new :envvar:`PYTHONHISTORY` environment variable can be used to change
+  the location of a ``.python_history`` file.
+  (Contributed by Levi Sabah and Zackery Spytz in :issue:`29779`.)
 
 New Modules
 ===========

Lib/site.py

@@ -393,6 +393,18 @@ def setcopyright():
 def sethelper():
     builtins.help = _sitebuiltins._Helper()
 
+def gethistoryfile():
+    """Check if the PYTHONHISTORY environment variable is set and define
+    it as the .python_history file.  If PYTHONHISTORY is not set, use the
+    default .python_history file.
+    """
+    if not sys.flags.ignore_environment:
+        history = os.environ.get("PYTHONHISTORY")
+        if history:
+            return history
+    return os.path.join(os.path.expanduser('~'),
+        '.python_history')
+
 def enablerlcompleter():
     """Enable default readline configuration on interactive prompts, by
     registering a sys.__interactivehook__.
@@ -428,13 +440,13 @@ def register_readline():
             pass
 
         if readline.get_current_history_length() == 0:
-            # If no history was loaded, default to .python_history.
+            # If no history was loaded, default to .python_history,
+            # or PYTHONHISTORY.
             # The guard is necessary to avoid doubling history size at
             # each interpreter exit when readline was already configured
             # through a PYTHONSTARTUP hook, see:
             # http://bugs.python.org/issue5845#msg198636
-            history = os.path.join(os.path.expanduser('~'),
-                                   '.python_history')
+            history = gethistoryfile()
             try:
                 readline.read_history_file(history)
             except OSError:

Lib/test/test_site.py

@@ -9,6 +9,7 @@
 from test import support
 from test.support import (captured_stderr, TESTFN, EnvironmentVarGuard,
                           change_cwd)
+from test.support.script_helper import assert_python_ok
 import builtins
 import os
 import sys
@@ -311,6 +312,19 @@ def test_no_home_directory(self):
             mock_addsitedir.assert_not_called()
             self.assertFalse(known_paths)
 
+    def test_gethistoryfile(self):
+        filename = 'file'
+        rc, out, err = assert_python_ok('-c',
+            f'import site; assert site.gethistoryfile() == "{filename}"',
+            PYTHONHISTORY=filename)
+        self.assertEqual(rc, 0)
+
+        # Check that PYTHONHISTORY is ignored in isolated mode.
+        rc, out, err = assert_python_ok('-I', '-c',
+            f'import site; assert site.gethistoryfile() != "{filename}"',
+            PYTHONHISTORY=filename)
+        self.assertEqual(rc, 0)
+
 
 class PthFile(object):
     """Helper class for handling testing of .pth files"""

Misc/NEWS.d/next/Library/2019-05-08-13-14-11.bpo-29779.jg33dp.rst

@@ -0,0 +1,2 @@
+Add a new :envvar:`PYTHONHISTORY` environment variable to set the location
+of a ``.python_history`` file.

Misc/python.man

@@ -502,6 +502,9 @@ show how long each import takes. This is exactly equivalent to setting
 .IP PYTHONBREAKPOINT
 If this environment variable is set to 0, it disables the default debugger. It
 can be set to the callable of your debugger of choice.
+.IP PYTHONHISTORY
+This environment variable can be used to set the location of a history file
+(on UNIX, it is \fI~/.python_history\fP by default).
 .SS Debug-mode variables
 Setting these variables only has an effect in a debug build of Python, that is,
 if Python was configured with the

Python/initconfig.c

@@ -95,7 +95,8 @@ static const char usage_6[] =
 "PYTHONBREAKPOINT: if this variable is set to 0, it disables the default\n"
 "   debugger. It can be set to the callable of your debugger of choice.\n"
 "PYTHONDEVMODE: enable the development mode.\n"
-"PYTHONPYCACHEPREFIX: root directory for bytecode cache (pyc) files.\n";
+"PYTHONPYCACHEPREFIX: root directory for bytecode cache (pyc) files.\n"
+"PYTHONHISTORY: the location of a .python_history file.\n";
 
 #if defined(MS_WINDOWS)
 #  define PYTHONHOMEHELP "<prefix>\\python{major}{minor}"