IPython/utils/rlineimpl.py

# -*- coding: utf-8 -*-
""" Imports and provides the 'correct' version of readline for the platform.

Readline is used throughout IPython as::

    import IPython.utils.rlineimpl as readline

In addition to normal readline stuff, this module provides have_readline
boolean and _outputfile variable used in IPython.utils.
"""

import sys
import warnings

if sys.platform == 'darwin':
    # dirty trick, to skip the system readline, because pip-installed readline
    # will never be found on OSX, since lib-dynload always comes ahead of site-packages
    from distutils import sysconfig
    lib_dynload = sysconfig.get_config_var('DESTSHARED')
    del sysconfig
    try:
        dynload_idx = sys.path.index(lib_dynload)
    except ValueError:
        dynload_idx = None
    else:
        sys.path.pop(dynload_idx)
try:
    from readline import *
    import readline as _rl
    have_readline = True
except ImportError:
    try:
        from pyreadline import *
        import pyreadline as _rl
        have_readline = True
    except ImportError:
        have_readline = False

if sys.platform == 'darwin':
    # dirty trick, part II:
    if dynload_idx is not None:
        # restore path
        sys.path.insert(dynload_idx, lib_dynload)
        if not have_readline:
            # *only* have system readline, try import again
            try:
                from readline import *
                import readline as _rl
                have_readline = True
            except ImportError:
                have_readline = False
            else:
                # if we want to warn about EPD / Fink having bad readline
                # we would do it here
                pass
    # cleanup dirty trick vars
    del dynload_idx, lib_dynload

if (sys.platform == 'win32' or sys.platform == 'cli') and have_readline:
    try:
        _outputfile=_rl.GetOutputFile()
    except AttributeError:
        warnings.warn("Failed GetOutputFile")
        have_readline = False

# Test to see if libedit is being used instead of GNU readline.
# Thanks to Boyd Waters for the original patch.
uses_libedit = False

if have_readline:
    # Official Python docs state that 'libedit' is in the docstring for libedit readline:
    uses_libedit = _rl.__doc__ and 'libedit' in _rl.__doc__
    # Note that many non-System Pythons also do not use proper readline,
    # but do not report libedit at all, nor are they linked dynamically against libedit.
    # known culprits of this include: EPD, Fink
    # There is not much we can do to detect this, until we find a specific failure
    # case, rather than relying on the readline module to self-identify as broken.

if uses_libedit and sys.platform == 'darwin':
    _rl.parse_and_bind("bind ^I rl_complete")
    warnings.warn('\n'.join(['', "*"*78,
        "libedit detected - readline will not be well behaved, including but not limited to:",
        "   * crashes on tab completion",
        "   * incorrect history navigation",
        "   * corrupting long-lines",
        "   * failure to wrap or indent lines properly",
        "It is highly recommended that you install readline, which is easy_installable:",
        "     easy_install -a readline",
        "Note that `pip install readline` generally DOES NOT WORK, because",
        "it installs to site-packages, which come *after* lib-dynload in sys.path,",
        "where readline is located.  It must be `easy_install -a readline`, or to a custom",
        "location on your PYTHONPATH (even --user comes after lib-dyload).",
        "*"*78]),
        RuntimeWarning)

# the clear_history() function was only introduced in Python 2.4 and is
# actually optional in the readline API, so we must explicitly check for its
# existence.  Some known platforms actually don't have it.  This thread:
# http://mail.python.org/pipermail/python-dev/2003-August/037845.html
# has the original discussion.

if have_readline:
    try:
        _rl.clear_history
    except AttributeError:
        def clear_history(): pass
        _rl.clear_history = clear_history