Tutorial :Seeing escape characters when pressing the arrow keys in python shell



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.


Solution:1

Looks like readline is not enabled. Check if PYTHONSTARTUP variable is defined, for me it points to /etc/pythonstart and that file is executed by the python process before going interactive, which setups readline/history handling.

Thanks to @chown here is the docs on this: http://docs.python.org/2/tutorial/interactive.html


Solution:2

I've solved this issue by installing readline package:

pip install readline  


Solution:3

On OS X, Xcode updates sometimes break readline. Solution:

brew uninstall readline  brew upgrade python3  brew install readline  pip3 install readline  

If the problem still persists, try to remove readline using pip and install it using easy_install:

pip3 uninstall readline  easy_install readline  


Solution:4

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!


Solution:5

  1. install readline-devel package.
  2. recompile python with readline module
  3. Bingo!


Solution:6

Here are the steps which worked for me in ubuntu 12.04 for python 3.3.

1) open teminal and write sudo apt-get install libreadline-dev

2) download the source file of python 3.3.2 from http://www.python.org/ftp/python/3.3.2/Python-3.3.2.tar.xz

3) extract it and navigate to the Python-3.3.2/ directory in a shell

4) execute the following command:

./configure  make  make test  sudo make install  


Solution:7

Was impacted after upgrading Mac to High Sierra, this successfully resolved it for me:

brew unlink python  xcode-select --install  brew install python  


Solution:8

On CentOS, I fix this by

yum install readline-devel

and then recompile python 3.4.

On OpenSUSE, I fix this by

pip3 install readline  

following Valerio Crini's answer.

Perhaps "pip3 install readline" is a general solution. Haven't tried on my CentOS.


Solution:9

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  


Solution:10

I fixed this by doing the following:

  • yum install readline-devel
  • pip install readline

    • I encountered another error here:

      gcc: readline/libreadline.a: No such file or directory

      gcc: readline/libhistory.a: No such file or directory

      I fixed this by installing patch:

      yum install patch

After that I managed to run pip install readline successfully which solved the escape characters in my python shell.

FYI, I'm using RedHat


Solution:11

If you use Anaconda Python, you can fix this by running:

conda install readline  

Worked for me!


Solution:12

I had problems with shell history(tab/arrows commands) of Python 3.6.x on Ubuntu 16.04 LTS.

Python 3.6.x was installed from source.

What solved for me was install the module "gnureadline" as said by user12345, using this command line:

sudo pip3.6 install gnureadline  

:)


Solution:13

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.


Solution:14

Did you call ssh with the -t parameter to tell ssh to allocate a virtual terminal for you?

From the man page:

-t
Force pseudo-tty allocation. This can be used to execute arbitrary screen-based programs on a remote machine, which can be very useful, e.g. when implementing menu services. Multiple -t options force tty allocation, even if ssh has no local tty.

Additionally you may also have to set the TERM environment variable on the server correctly as suggested in another post.


Solution:15

For those using conda, installing the readline package from conda-forge channel will fix the problem:

conda install -c conda-forge readline=6.2  


Solution:16

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.


Solution:17

Try getting a key code library running on the server. If that does not work try to download a library with read-key ability.


Solution:18

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.


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