Activate a Virtualenv with a Python Script

How can I activate the virtual environment from a python script and execute further instructions while inside of it?

There is a number of things wrong here. When you run a subprocess, the environment it creates disappears when the subprocess exits.

What you can do is wrap Python inside Python, something like

import subprocess

env_name = "env_new"
subprocess.run(["py", "-m", "venv", env_name])

subprocess.run(["%s/bin/python" % env_name, "-c", """
    the rest of your Python code here
    """])

which of course is just a rather pointless complication, and better written as a shell script.

#!/bin/bash

py -m venv env_new
. ./env_new/Scripts/activate
pip install -r requirements.txt
python ./your_real_script_here.py

Activate virtual environment from a python script

Looks like this answer I linked doesn't work for Python 3, but in the comments for the answer in that post I found the following from @Calimo which worked for me:

activate_this_file = "/path/to/venv/bin/activate_this.py"
exec(compile(open(activate_this_file, "rb").read(), activate_this_file, 'exec'), dict(__file__=activate_this_file))

Edit: After some discussion it looks like the real issue was using subprocess without specifying the correct environment. By default subprocess spawns a new process using the global environment. Specify the desired virtual environment by providing the env arg when calling subprocess, ex after activating the virtual environment with the code above:

venv= os.environ.copy()
subprocess.check_all(["pip3", "install", "flask"], env=venv)

Activating a Python virtual environment and calling python script inside another python script

Each virtualenv has its own python executable which you can use directly to execute the script.

Using subprocess (more versatile than os.system):

import subprocess

venv_python = '/path/to/other/venv/bin/python'
args = [venv_python, 'my_script.py', 'arg1', 'arg2', 'arg3']
subprocess.run(args)    

Activating virtualenv from within Python script

The very 1^st line of activate (note that VEnv is installed on Win, but this shouldn't be a problem):

# This file must be used with "source bin/activate" *from bash* 

That, and the lines below should tell you that activate is a (Bourne) shell file.

[Python 3]: compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1) on the other hand, works with Python source code.

So, in order to execute the file, you'd need to use other ways, e.g. [Python 3]: subprocess - Subprocess management.
You can check how I've used it: [SO]: How to effectively convert a POSIX path to Windows path with Python in Cygwin? (@CristiFati's answer).

But, I really don't see the point of doing all this, you probably misunderstood your colleague's suggestion.

Also note that even if you do manage to do it this way, all the environment variables will only be set in the calling process, so it will pretty much be unusable (well, unless you also execute your script from there too).

You should go the recommended way ([PyPA]: Virtualenv - User Guide), and that is (from bash):

source /path/to/Django/ENV/bin/activate
python your_project_startup_script.py  # (as I recall, it's manage.py)

How to create Python Virtual environment within a python script

To create a virtual env from inside a python script you can use the virtualenv python module.

It pretty much comes down to a single line of code.

import virtualenv
import os

venv_dir = os.path.join(os.path.expanduser("~"), ".venv")
virtualenv.create_environment(venv_dir)

You can then activate this environment by accessing the activate_this.py file in your .venv folder, and install custom packages using pip module.

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