Python shell: Arrow keys not working in PuTTY

[Steven D'Aprano]

Laura Creighton wrote:

> DO NOT REBUILD PYTHON ON CENTOS!
> 
> It can break the whole package management system
> which depends on having a particular version of python installed.
> 
> If you are running Centos you need to use virtualenv to be safe.
> 
> Laura


Almost right!

You can install Python from source. Unzip the source tar ball, cd into the 
source directory, and run:

./configure
make

BUT do *not* run `make install` as that will overwrite your system Python 
and Bad Things will happen. Instead, run `make altinstall`.

Now you will have two Python installs, the stock-standard system Python is 
available as "python", and the newly-installed one as "pythonX.Y" (for 
version X.Y).

What I do is then add

alias python /usr/local/bin/pythonX.Y

to my .bashrc file, and use the new one. (Don't forget to change the X.Y to 
whatever version you actually used.)

What if you accidentally blow away the system Python by running `make 
install`? You probably won't be able to use yum to fix it, since yum relies 
on the system Python. Fortunately, you haven't actually *removed* the system 
Python, it's still there just hiding. First, find out which version of 
Python your system Python is:


[steve at ando ~]$ ls -l /usr/bin/python*
-rwxr-xr-x 2 root root 5708 Jan  9  2013 /usr/bin/python
lrwxrwxrwx 1 root root    6 Jan 22  2013 /usr/bin/python2 -> python
-rwxr-xr-x 2 root root 5708 Jan  9  2013 /usr/bin/python2.4

This tells me that the system Python is 2.4 (well actually I already knew 
that). /usr/bin/python here is a hard-link to the python2.4 executable. If I 
had accidentally killed the system Python, I would see something like:

-rwxr-xr-x 2 root root 6789 Feb 24  2015 /usr/bin/python
lrwxrwxrwx 1 root root    6 Jan 22  2013 /usr/bin/python2 -> python
-rwxr-xr-x 1 root root 5708 Jan  9  2013 /usr/bin/python2.4
-rwxr-xr-x 2 root root 6789 Feb 24  2015 /usr/bin/python2.7

The /usr/bin/python is now hard-linked to the newly installed version. As 
root:

rm /usr/bin/python  # Die, imposter!
ln /usr/bin/python2.4 /usr/bin/python  # Revive the system Python.

All fixed!


-- 
Steven