Seeing escape characters when pressing the arrow k

Question

In shells like the interactive python shell, you can usually use the arrow keys to move around in the current line or get previous commands (with arrow-up) etc.

But after I ssh into another machine and start python there, I get sessions like:

>>> import os 
>>> ^[[A    

where the last character comes from arrow-up. Or, using arrow-left:

>>> impor^[[D

How can I fix this?

In the regular bash, arrow keys work fine. The weird behavior is just in the interactive python (or perl etc.) shell.

Answer 1

How's your env variable $TERM set [a] when things work fine and [b] when they don't? Env settings are often the key to such problems.

Answer 2

I was trying build Python 2.7 on Ubuntu 14.0. You will need libreadline-dev. However, if you get it from apt-get, the current version is 6.3, which is incompatible with Python 2.7 (not sure about Python 3). For example, the data type "Function" and "CPPFunction", which were defined in previous versions of readline has been removed in 6.3, as reported here:

https://github.com/yyuu/pyenv/issues/126

That is to say you need to get the source code of an earlier version of readline. I installed libreadline 5.2 from apt-get for the library, and get the source code of 5.2 for the header files. Put them in /usr/include.

Finally the issue has been resolved.

Answer 3

On OS X, I have different problem.

When I using system python shell, the keys is no problem, but problem in virtualenv. I'd try to reinstall/upgrade virtualenv/readline and nothing fixed.

While I try to import readline in problem python shell, get this error message:

ImportError: dlopen(/Users/raptor/.virtualenvs/bottle/lib/python2.7/lib-dynload/readline.so, 2): Library not loaded: /usr/local/opt/readline/lib/libreadline.6.dylib
Referenced from: /Users/raptor/.virtualenvs/bottle/lib/python2.7/lib-dynload/readline.so
Reason: image not found

Cause there is /usr/local/opt/readline/lib/libreadline.7.dylib but not libreadline.6.dylib, so I make a symbol link:

ln libreadline.7.dylib libreadline.6.dylib

Problem has been solved!

Answer 4

On OS X, using python 3.5 and virtualenv

$ pip install gnureadline

In the interpreter do:

import gnureadline

Now arrow keys should work properly.

---

Additional information...

Note that as of Oct 1, 2015 - readline has been DEPRECATED (source https://github.com/ludwigschwardt/python-readline)

Use gnureadline instead (see: https://github.com/ludwigschwardt/python-gnureadline)

If I install readline instead of gnureadline using python 3.5, I receive errors after attempt to import in the interpreter:

>>> import readline
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dlopen(/Users/pi/tmp/python-readline-test/.venv/lib/python3.5/readline.so, 2): Library not loaded: /usr/local/opt/readline/lib/libreadline.6.dylib
  Referenced from: /Users/pi/tmp/python-readline-test/.venv/lib/python3.5/readline.so
  Reason: image not found

Answer 5

Have you tried using a different SSH client? Some SSH clients have special, built-in keymappings for different remote processes. I ran into this one a lot with emacs.

What client are you using? I'd recommend trying Putty and SecureCRT to compare their behavior.

Answer 6

readline module has been deprecated which will cause invalid pointer error in latest python versions when executing quit() or exit() in python shell. pip install gnureadline instead