Add a python startup file for interactive sessions

This is a preparation to move the .python_history file into an XDG
directory -> $XDG_CACHE_HOME/python/history

dotfiles/.config/python/startup.py

@@ -0,0 +1,60 @@
+import sys
+
+"""Enable default readline configuration on interactive prompts, by
+registering a sys.__interactivehook__.
+
+If the readline module can be imported, the hook will set the Tab key
+as completion key and register ~/.python_history as history file.
+This can be overridden in the sitecustomize or usercustomize module,
+or in a PYTHONSTARTUP file.
+"""
+def register_readline():
+    import atexit
+    try:
+        import readline
+        import rlcompleter
+    except ImportError:
+        return
+
+    # Reading the initialization (config) file may not be enough to set a
+    # completion key, so we set one first and then read the file.
+    readline_doc = getattr(readline, '__doc__', '')
+    if readline_doc is not None and 'libedit' in readline_doc:
+        readline.parse_and_bind('bind ^I rl_complete')
+    else:
+        readline.parse_and_bind('tab: complete')
+
+    try:
+        readline.read_init_file()
+    except OSError:
+        # An OSError here could have many causes, but the most likely one
+        # is that there's no .inputrc file (or .editrc file in the case of
+        # Mac OS X + libedit) in the expected location.  In that case, we
+        # want to ignore the exception.
+        pass
+
+    if readline.get_current_history_length() == 0:
+        # If no history was loaded, default to .python_history.
+        # 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')
+        try:
+            readline.read_history_file(history)
+        except OSError:
+            pass
+
+        def write_history():
+            try:
+                readline.write_history_file(history)
+            except (FileNotFoundError, PermissionError):
+                # home directory does not exist or is not writable
+                # https://bugs.python.org/issue19891
+                pass
+
+        atexit.register(write_history)
+
+sys.__interactivehook__ = register_readline
+