python 2 instead of python 3 as the (temporary) default python?

on my com开发者_如何学Goputer

~$ python -V
 Python 3.2.1

but I get into problems when I run some python programs. my guess is (or at least I want to try this) that there is some backward compatibility issues, and I want to run those python scripts with

 python2 2.7.2-2

which is also installed on my system but I do not know how to make it as the (temporary) default python. The python script starts with

 #!/usr/bin/env python

and I am using arch linux.

You can use virtualenv

# Use this to create your temporary python "install"
# (Assuming that is the correct path to the python interpreter you want to use.)
virtualenv -p /usr/bin/python2.7 --distribute temp-python

# Type this command when you want to use your temporary python.
# While you are using your temporary python you will also have access to a temporary pip,
# which will keep all packages installed with it separate from your main python install.
# A shorter version of this command would be ". temp-python/bin/activate"
source temp-python/bin/activate

# When you no longer wish to use you temporary python type
deactivate

Enjoy!

mkdir ~/bin
PATH=~/bin:$PATH
ln -s /usr/bin/python2 ~/bin/python

To stop using python2, exit or rm ~/bin/python.

Just call the script using something like python2.7 or python2 instead of just python.

So:

python2 myscript.py

instead of:

python myscript.py

What you could alternatively do is to replace the symbolic link "python" in /usr/bin which currently links to python3 with a link to the required python2/2.x executable. Then you could just call it as you would with python 3.

You don't want a "temporary default Python"

You want the 2.7 scripts to start with

/usr/bin/env python2.7

And you want the 3.2 scripts to begin with

/usr/bin/env python3.2

There's really no use for a "default" Python. And the idea of a "temporary default" is just a road to absolute confusion.

Remember.

Explicit is better than Implicit.

You could use alias python="/usr/bin/python2.7":

bash-3.2$ alias
bash-3.2$ python
Python 2.7.6 (v2.7.6:3a1db0d2747e, Nov 10 2013, 00:42:54) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> ^D
bash-3.2$ alias python="/usr/bin/python3.3"
bash-3.2$ python
Python 3.3.3 (v3.3.3:c3896275c0f6, Nov 16 2013, 23:39:35) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 

If you have some problems with virtualenv,

You can use it:

sudo ln -sf python2 /usr/bin/python

and

sudo ln -sf python3 /usr/bin/python

Use python command to launch scripts, not shell directly. E.g.

  python2 /usr/bin/command

AFAIK this is the recommended method to workaround scripts with bad env interpreter line.

As an alternative to virtualenv, you can use anaconda.

On Linux, to create an environment with python 2.7:

conda create -n python2p7 python=2.7
source activate python2p7

To deactivate it, you do:

source deactivate

It is possible to install other package inside your environment.

I think it is easier to use update-alternatives:

sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1