Why is the Python readline module not available on OS X?

Question

The documentation of the Python readline module says "Availability: Unix". However, it doesn't appear to be available on OS X, although other modules marked as Unix are available. Here is what I'm using:

$ uname -a
Darwin greg.local 8.11.1 Darwin Kernel Version 8.11.1: Wed Oct 10 18:23:28 PDT 2007; root:xnu-792.25.20~1/RELEASE_I386 i386 i386
$ which python
/usr/bin/python
$ python
Python 2.3.5 (#1, Nov 26 2007, 09:16:55) 
[GCC 4.0.1 (Apple Computer, Inc. build 5363) (+4864187)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import readline
Traceback (most recent call last):
  File "", line 1, in ?
ImportError: No module named readline
>>> 

I have also installed Python 2.5 through MacPorts but readline is not available there either.

What can I do to provide readline functionality for Python's raw_input() function on OS X?

Answer 1

It's not shipped in OS X because of licensing issues (restrictions brought to you by the GPL).

Macports python should be fine if you have the readline package installed.

Answer 2

Have you tried to install the py-readline (or py25-readline for Python 2.5) port?

Also, in the snippet above, you are NOT using the MacPort python, but rather the Apple Python.

The MacPort version should be located in the /opt/local directory structure. You should check your path.

Answer 3

You should be able to get readline support on Mac's native Python. Apparently it's implemented via BSD's editline, and you have to start it up slightly differently. I just tested this on a Mac, and it works fine (OS X 10.5.7). See man python for more details, the section "Interactive Input Editing and History Substitution" - mirrored on the web here.

luga ~ $ python 
Python 2.5.1 (r251:54863, Feb  6 2009, 19:02:12) 
[GCC 4.0.1 (Apple Inc. build 5465)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import rlcompleter
>>> import readline
>>>