How to switch between python 2.7 to python 3 from

问题:

I'm trying to find the best way to switch between the two python compilers 2.7 to 3.3 If I run python from cmd, I would you use something like

python ex1.py

where I set "python" from window environment variable from my computer properties to point to either python 3.3 or 2.7 one or another.

I am wondering there is an easy way to switch between the two from cmd line ?

回答1:

For Windows 7, I just rename the python.exe from the Python 3 folder to python3.exe and add the path into the environment variables. Using that, I can execute python test_script.py and the script runs with Python 2.7 and when I do python3 test_script.py, it runs the script in Python 3.

To add Python 3 to the environment variables, follow these steps -

1. Right Click on My Computer and go to Properties.
2. Go to Advanced System Settings.
3. Click on Environment Variables and edit PATH and add the path to your Python 3 installation directory.

For example,

回答2:

No need for "tricks". Python 3.3 comes with PyLauncher "py.exe", installs it in the path, and registers it as the ".py" extension handler. With it, a special comment at the top of a script tells the launcher which version of Python to run:

#!python2
print "hello"

Or

#!python3
print("hello")

From the command line:

Py -3 hello.py

Or

Py -2 hello.py

See 3.4. Python Launcher for Windows

回答3:

They are 3 ways you can achieve this using the py command (py-launcher) in python 3, virtual environment or configuring your default python system path. For illustration purpose, you may see tutorial https://www.youtube.com/watch?v=ynDlb0n27cw&t=38s

回答4:

You can try to rename the python executable in the python3 folder to python3, that is if it was named python formally... it worked for me