Why do I get the empty tuple if I type / in iPython?

Question

Open up iPython and type this:

/

Hit enter and wonder about the result:

()

You cannot assign it, my guess it has something to do with the shell functionality.

Edit:

You can assign it with:

 p = Out[xx]

But not directly:

 p = / 

will give:

SyntaxError

It is indeed an empty tuple.

Answer 1

It is a convenience feature for callable objects/names. It's not an empty tuple, but parentheses completion. From iPython's help system (?):

• Auto-parentheses and auto-quotes (adapted from Nathan Gray's LazyPython)

  1. Auto-parentheses

     Callable objects (i.e. functions, methods, etc) can be invoked like this (notice the commas between the arguments)::

     In [1]: callable_ob arg1, arg2, arg3

     and the input will be translated to this::

     callable_ob(arg1, arg2, arg3)

     This feature is off by default (in rare cases it can produce undesirable side-effects), but you can activate it at the command-line by starting IPython with --autocall 1, set it permanently in your configuration file, or turn on at runtime with %autocall 1.

     You can force auto-parentheses by using '/' as the first character of a line. For example::

     In [1]: /globals # becomes 'globals()'