Merge pull request #4606 from takluyver/optional-pythonstartup

Make running PYTHONSTARTUP optional

IPython/core/shellapp.py

@@ -172,6 +172,10 b' class InteractiveShellApp(Configurable):'
     exec_files = List(Unicode, config=True,
         help="""List of files to run at IPython startup."""
     )
+    exec_PYTHONSTARTUP = Bool(True, config=True,
+        help="""Run the file referenced by the PYTHONSTARTUP environment
+        variable at IPython startup."""
+    )
     file_to_run = Unicode('', config=True,
         help="""A file to be run""")
 
@@ -354,8 +358,9 b' class InteractiveShellApp(Configurable):'
         """Run files from profile startup directory"""
         startup_dir = self.profile_dir.startup_dir
         startup_files = []
-        if os.environ.get('PYTHONSTARTUP', False):
-            startup_files.append(os.environ['PYTHONSTARTUP'])
+        if self.exec_PYTHONSTARTUP:
+            if os.environ.get('PYTHONSTARTUP', False):
+                startup_files.append(os.environ['PYTHONSTARTUP'])
         startup_files += glob.glob(os.path.join(startup_dir, '*.py'))
         startup_files += glob.glob(os.path.join(startup_dir, '*.ipy'))
         if not startup_files:

docs/source/interactive/reference.rst

@@ -761,13 +761,14 b" won't work::"
 IPython as your default Python environment
 ==========================================
 
-Python honors the environment variable PYTHONSTARTUP and will execute at
-startup the file referenced by this variable. If you put the following code at
-the end of that file, then IPython will be your working environment anytime you
-start Python::
+Python honors the environment variable :envvar:`PYTHONSTARTUP` and will
+execute at startup the file referenced by this variable. If you put the
+following code at the end of that file, then IPython will be your working
+environment anytime you start Python::
 
-    from IPython.frontend.terminal.ipapp import launch_new_instance
-    launch_new_instance()
+    import os, IPython
+    os.environ['PYTHONSTARTUP'] = ''  # Prevent running this again
+    IPython.start_ipython()
     raise SystemExit
 
 The ``raise SystemExit`` is needed to exit Python when