How to specify python version used to create Virtual Environment?

53
votes

My Python virtual environments use python3.6 when I create them using virtualenv

~ $ virtualenv my_env

but I need to use python3.5 as 3.6 is not currently supported by Opencv3.

I've tried using the --python=<py_version> flag when creating a virtual environment but this doesn't work.

How do I specify the python (3.x) version to install using virtualenv for Mac and/or Linux?

5
pythonpython-3.xvirtualenv
Have you installed Python 3.5 on your computer? You're right in passing the --python flag, so something else about your environment or invocation is wrong here. Can you give the error message? - Cody Piersall
Yesterday I tried running conda install python=3.5 inside of my activated virtual environment thinking that this would change the python dist inside my env but instead it changed the local version. I changed back to 3.6 but now I run into this problem but the answer there does not work for me. oh god what did I do - Danoram
@CodyPiersall It seems that installing miniconda changed the path var to /Users/.../miniconda3/bin: which is incompatible with the python version virtualenv was using. Removing /Users/.../miniconda3/bin from the path fixes the issue but then I can't use conda... I know this is now a separate issue but any ideas how I can add it back to the path without messing up virtualenv? - Danoram
I just want to give an hint for those using Windows(and using Powershell). In this case make sure to explicitly write the .exe, that is what I mean: virtualenv -p C:\PythonVersionFolder\Python.exe EnvName. Otherwise you could get the PermissionError: [WinError 5] denied Access - Carmine Tambascia
Possible duplicate of Use different Python version with virtualenv - Trevor Boyd Smith

5 Answers

51
votes

Assuming that you have installed python3 or any desired version of Python (2.6, 2.7, 3.5, 3.6), Now while creating the virtual environment directly pass the python executable path. Hence here are few valid example

$ virtualenv new_p2_env # Creates a new default python environment (usually python 2)

$ virtualenv -p python3 new_p3_env # Creates a new default python3 (python3 must be a valid command i.e found in the PATH)

And last

# Directly point to any version of python binary, this can be even another virtualenv's bin/python. 
$ virtualenv -p /path/to/any/bin/python new_env
11
votes

Alternatively, I think you could use the specific version of Python itself to create the virtual environment. That way, you'll know for sure it's the correct version:

$ python3.5 -m venv test35
$ ./test35/bin/python
Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 26 2016, 10:47:25)
[GCC 4.2.1 (Apple Inc. build ) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

Reference at https://docs.python.org/3.5/library/venv.html

7
votes

As of version 3.3, python includes a package named venv. However that package doesn't provide the same functionalities as the traditional virtualenv package.

venv allows creating virtual environments only for the version of python it's installed for. virtualenv allows creating virtual environments for different versions of python by providing the path to the binary.

Creating virtual envs for different versions of python:

So assuming one has python 2.7 and python 3.6 installed in /path/to/ and wants to create the virtual env named respectively env-py36 with python 3.6 and env-py27 with python 2.7

# create a virtual env with python3's venv :
/path/to/python36/bin/python3 -m venv /my/python-venvs/env-py36
. /my/python-venvs/env-py36/bin/activate
# we're now running python 3's "env-py36" virtual env, we want to install the "virtualenv" package
pip install virtualenv
deactivate
# now use virtualenv to create a virtual environment for python 2.7
/my/python-venvs/env-py36/bin/virtualenv --python=/path/to/python27/bin/python /my/python-venvs/env-py27

Using python 3.3+ venv

Python 3.3+ :

/path/to/python3/bin/python3 -m venv ENV_DIR

Python 3.3 to 3.5 (deprecated in 3.6+) :

/path/to/python3/bin/pyvenv ENV_DIR

Sources:

2
votes

I working on all ubuntu and MacOS

Ubuntu : virtualenv -p python3.6 environment_file

Mac OS : virtualenv -p python3.6 environment_file

I think it be same

2
votes

I had this issue (and came here) but under Windows. Python 3.9 was installed on one system but it had issues with code developed under 3.7. I wanted to use a virtual environment to downgrade to 3.7 to help debug the issue. Using Python Launcher for Windows:

py -3.7 -m venv my_env

in the python project folder did the trick for me.