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.

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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!

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

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

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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.

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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.
>>> 

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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

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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.

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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.

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I think it is easier to use update-alternatives:

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