Installed Anaconda for python 2 and 3. Can't run 2

Question

I installed both versions of Anaconda for Python 2 and 3.

I added path.

I use Anaconda prompt.

python program.py

It assumes I am using Python 3. For example, it can't understand:

print "hello!"

I tried:

py program.py
py -2 program.py

But they didn't work. How can I run a Python 2 program?

If I type:

python

in the Acaconda prompt, then it says:

python 3.5.1. Anaconda 2.4.1

So the prompt is assuming I am using Python 3.

But I have programs written in Python 2 AND programs written in Python 3.

I want to switch between the two smoothly. How should I do this?

Answer 1

The simples solution is to create an environment for Python 2:

conda create -n py27 python=2.7 anaconda

This will take a few seconds and will show you a ling list of packages it is going to install. Just press enter and wait.

Once finished activate your new environment.

On Windows:

activate py27 

On other platforms:

source activate py27 

The prompt should change to (py27). Now you use Python 2.7.

Deactivate with:

deactivate 

Now you are back to Python 3. You can run both versions in two terminal windows at the same time. You can create environments for other Python versions:

conda create -n py34 python=3.4 anaconda
conda create -n py35 python=3.5 anaconda

If you don't want the full Anaconda installation in an environment, create one with all packages:

conda create -n myenv python=3.5
source activate myenv

and install what you need. For example:

conda install numpy pytables sympy

You can define a bash function in your .profile or .bashrc:

py27() {
exec &>/dev/null
source activate py27
exec &>/dev/tty
python $*
exec &>/dev/null
source deactivate
exec &>/dev/tty
}

Now you can run your program with Python 27, provided you created an environment with this name using Python 2.7:

py27 myscript.py

You can generalize further an create a command for Python 2.6, 2,7, 3.3, 3.4, and 3.5:

pyxx() {
exec &>/dev/null
source activate $1
exec &>/dev/tty
python ${*:2}
exec &>/dev/null
source deactivate
exec &>/dev/tty
}


py26()
{
    pyxx py26 $*
}

py27()
{
    pyxx py27 $*
}

py33()
{
    pyxx py33 $*
}

py34()
{
    pyxx py34 $*
}

py35()
{
    pyxx py35 $*
}

This assumes you already created environments with the according names and Python versions.