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Activating Python Virtual env in Batch file

I'm trying to make a batch script (called run_windows) that check if the python virtual environment exists and if not, create it then activate it, install the requirements and finally run some python code.
set "VIRTUAL_ENV=mat_visualizer_env"
:read_mat
%VIRTUAL_ENV%\Scripts\activate
pip install -r app_files/requirements.txt
python -c "import sys; sys.path.insert(1,'app_files'); from main import visualize_mat_eeg; visualize_mat_eeg('%1')"
pause
EXIT /B 0
IF EXIST "%VIRTUAL_ENV%\Scripts\activate.bat" (
CALL :read_mat
) ELSE (
pip install virtualenv
python -m venv mat_visualizer_env
CALL :read_mat
)
However, when I run my script, the code exits at line 4: %VIRTUAL_ENV%\Scripts\activate with no errors:

Few things:
Running the .bat or bash version of activate in powershell is not predictable, Activate.ps1 is found in newer releases. It could probably be used with older versions if copied from a newer release.
Scripts in windows (.bat or .cmd in windows) processes from top down, :<ANCHOR> is not skipped like a Sub or Function would be.
I have only worked with the Conda version of activate.ps1 and it adds some nice commands. Had a quick look in standard Python 3.10.5 and it does not add commands but should work fine.
Edit: Added that while working, is not the best option to use the bash version of activate

Here is a quick example of your batch file rearranged, and using the Call command as previously instructed.
#Echo Off
Set "VIRTUAL_ENV=mat_visualizer_env"
If Not Exist "%VIRTUAL_ENV%\Scripts\activate.bat" (
pip.exe install virtualenv
python.exe -m venv %VIRTUAL_ENV%
)
If Not Exist "%VIRTUAL_ENV%\Scripts\activate.bat" Exit /B 1
Call "%VIRTUAL_ENV%\Scripts\activate.bat"
pip.exe install -r app_files/requirements.txt
python.exe -c "import sys; sys.path.insert(1,'app_files'); from main import visualize_mat_eeg; visualize_mat_eeg('%~1')"
Pause
Exit /B 0
Please note, that there is no working directory defined in this script, as was yours, and therefore no way to guarantee that when run, the relative paths point to the intended locations. Additionally, you have not made it clear what %1 was supposed to be, or where it was coming from, so I cannot guarantee whether that is correct.

Python Package on GitHub

I made a python (3) package and I have been trying to upload it on Github. I also know how to push and install a git using pip. To test if it works as anticipated, I made a virtual environment on my local computer (linux) and pip installed my already pushed private package in there without a problem.
The issue is that I don't know how to access it!!! (I know how to activate and use virtualenvs; I don't know how to call my package) My package has a main interface that one would need to call it in terminal as follows:
python3 myui.py some_args *.data
and it's supposed to create some files where it's called. In other words, it's not exactly a module like numpy to be imported. I have watched/read many tutorials and documentations on the web and tbh I'm lost here.

You are looking for the -m flag. If you installed everything correctly, then the following command should allow you to run your script (based on your example). Note that you shouldn't add the file extension '.py'.
python3 -m myui some args *.data
If you have an actual package (directory with __init__.py file and more) instead of a module (a single .py file), then you can add a __main__.py file to that package. Python will execute this script when you use the -m flag with the package's name, in the same way as shown above.
python3 -m mypackage some args *.data
If you want to run a different script that is nested somewhere inside of that package, you can still run it by specifying its module name:
python3 -m mypackage.subpackage.myscript some args *.data
Another common way to make your script available uses the setup script (setup.py) or setup configuration file (setup.cfg) that is used to install the module or package. In that case, you can add an entry point to map a command to a specific module/function/etc. (as described in this Python packaging tutorial) so that you can run that command instead of having to use the -m flag with Python.
$ mycommand some args *.data

Pytest run by test explorer of vscode does not find modules installed by pip in dev mode

Running tests on my project code installed with pip in developer mode (pip install -e .) does work by executing pytest from the command line. However, running the same tests within the same Python virtualenv using the Test Explorer UI of Visual Studio Code does not work, Python raises ModuleNotFoundErrors.
I confirmed that my package is installed by pip list -v, which prints:
myproject 0.0.0 /path/to/myproject
Furthermore, I wrote failing test to get the Python path during test execution:
import sys
def test_some_test():
print(sys.executable)
print(sys.path)
assert False
This confirms that the Python executable is the one from the virtualenv where my project code is installed. But the sys.path differs between the Test Explorer run and the command line run. The Test Explorer run does not include the /path/to/myproject in the sys.path, whereas the command line run does. Obviously, if the project's path is included in the sys.path, the package can be imported. Why is it missing from the Test Explorer UI run? How to make the Test Explorer use the packages installed in develop mode with pip?
I should add that the modules I try to import in my tests are in a package themselves, called mylib. So the actual import in my test is like
from mylib import function_under_test
def test_function_under_test():
...

Update
This issue is fixed now. It just works.
Old Answer
Fiddling around with the issue more, I found that this is a bug in the Python extension for vscode, cf. issues
14579, and 14570 on github.com.
As a work-around one may either install the Little Fox Team Test Explorer UI extension, or an old version of the Microsoft Python extension (v2020.9.114305).

python27 and python3 are not not recognized as an internal or external command, operable program or batch file [duplicate]

I am using Python 3.5.2 version on Windows 7 and tried using python3 app.py. I am getting this error message:
'python3' is not recognized as an internal or external command,
operable program or batch file.
Is there any specific cause about why the python3 command is not working?
I also verified that the PATH is added to environment variables.

There is no python3.exe file, that is why it fails.
Try:
py
instead.
py is just a launcher for python.exe. If you have more than one python versions installed on your machine (2.x, 3.x) you can specify what version of python to launch by
py -2 or
py -3

You can also try this:
Go to the path where Python is installed in your system. For me it was something like C:\Users\\Local Settings\Application Data\Programs\Python\Python37
In this folder, you'll find a python executable. Just create a duplicate and rename it to python3. Works every time.

Python3.exe is not defined in windows
Specify the path for required version of python when you need to used it by creating virtual environment for your project
Python 3
virtualenv --python=C:\PATH_TO_PYTHON\python.exe environment
Python2
virtualenv --python=C:\PATH_TO_PYTHON\python.exe environment
then activate the environment using
.\environment\Scripts\activate.ps1

Yes, I think for Windows users you need to change all the python3 calls to python to solve your original error. This change will run the Python version set in your current environment. If you need to keep this call as it is (aka python3) because you are working in cross-platform or for any other reason, then a work around is to create a soft link. To create it, go to the folder that contains the Python executable and create the link. For example, this worked in my case in Windows 10 using mklink:
cd C:\Python3
mklink python3.exe python.exe
Use a (soft) symbolic link in Linux:
cd /usr/bin/python3
ln -s python.exe python3.exe

In my case I have a git hook on commit, specified by admin. So it was not very convenient for me to change the script (with python3 calls).
And the simplest workaround was just to copy python.exe to python3.exe.
Now I could launch both python and python3.

If python2 is not installed on your computer, you can try with just python instead of python3

For Python 27
virtualenv -p C:\Python27\python.exe django_concurrent_env
For Pyton36
virtualenv -p C:\Python36\python.exe django_concurrent_env

Enter the command to start up the server in that directory:
py -3.7 -m http.server

I had a related issue after installing windows 11, where python3 in cmd would open the windows store. I was able to sort it out between this post and this other one. In short, I reinstalled python and made sure to add it to PATH. Then, in settings, Apps > Apps & Features > App Execution aliases. Here, all I had to do was make sure that every single python .exe (including idle and pip) were turned off EXCEPT FOR the python3.exe alias. Now it works like a charm.
FWIW:
The root of this issue is not with you or with python. Apparently, Microsoft wanted to make installing python easier for young kiddos getting interested in coding, so they automatically add an executable to PATH. For those of us that already have this executable, it can cause these issues.

Found out instead press the play button the top right and it should work in visual studios:
Do not disable according to first answer
Saying python3 in the command will not work by default.
After figuring out the problem with the modules (Solution): https://youtu.be/paRXeLurjE4
Summary:
To import python modules in case of problem to import modules:
Hover over python in search:
Click open in folder
Hover over and right click
click properties
copy everything in path before \python.exe
close those windows
For cmd (administrator):
cd --path that was copied--
then python -m pip install --upgrade pip
cd Scripts
pip install "Name of Package" such as pip install --module (package) --

Im on win10 and have 3.7, 3.8 and 3.10 installed.
For me "python" launches version 3.10 and does not accept commands (like -3.7), "py" launches newest version but does accept commands, and "python3" does nothing.
Uninstalled 3.10 and "python" now does nothing, and "py" launches 3.8.

I am unable to add a comment, but the mlink option presented in this answer above https://stackoverflow.com/a/55229666/8441472 by #Stanislav preserves cross-platform shebangs at the top of scripts (#!/usr/bin/env python3) and launches the right python.
(Even if you install python from python.org, Windows will direct you to the app marketplace nowadays if you type python3 on the command line. If you type python on the same cli it will launch the python.org version repl. It leads to scripts that generate no output, but more likely silently failed completely. I don't know ho common this is but have experienced it on a couple of different devices)
If you have this at the top of your script to ensure you launch python3 and don't feel like editing everything you own, it is not a bad approach at all... lol.

Execute an installed Python package as a script?

Is there a way to enable a package to be executed as a script? For example:
[~]# easy_install /path/to/foo.egg
...
[~]# python -m foo --name World
Hello World
I've tried creating a __main__.py file inside my package but it's not being executed (I'm using Python 2.6). The following error is raised:
foo is a package and cannot be directly executed
The structure of my package is as follows:
foo/
setup.py
foo/
__init__.py
__main__.py
Running python -m foo.__main__ --name World works as expected, but I would prefer the former way of execution. Is this possible?

This is a regression in Python 2.6. See issue2571:
The ability to execute packages was never intended, since doing so
breaks imports in a variety of subtle ways. It was actually a bug in
2.5 that it was permitted at all, so 2.6 not only disabled it again, but also added a test to make sure it stays disabled (2.4 correctly
rejected it with an ImportError, just as 2.6 does).
You have a few options, you can either always run it specifying main:
$ python -m module.__main__
Or you can write a shell script wrapper that detects the python version and then executes it in the different style.
Or you can execute code on the command line that will import and then run the module, and then perhaps place that in a shell script:
$ python -c "import module; module.main()"
In my own command-line projects I have both the shell script that catches errors (python not being installed, etc.) but the shell script will also execute the import code and detect if the necessary modules have been installed and prompt an error (with a helpful link or install text).

I think this may be a limitation of Python 2.6. I've tested it, and executing a package (either in . or installed from an egg with easy_install) with the -m option works fine in 2.7, but not in 2.6. For example, on my system (Ubuntu) with a test package called pkg_exec in the current directory, and where __main__.py simply prints sys.argv:
xx#xx:~/tmp/pkg_exec$ python2.6 -m pkg_exec
/usr/bin/python2.6: pkg_exec is a package and cannot be directly executed
xx#xx:~/tmp/pkg_exec$ python2.7 -m pkg_exec
['/home/xx/tmp/pkg_exec/pkg_exec/__main__.py']
Also, according to the 2.7 docs:
Changed in version 2.7: Supply the package name to run a __main__ submodule.

Yes, you can do that if the script has the __main__ section.
Of course, you can't execute a package if it is a directory. But if you can run the script itself (say it starts with #!/usr/bin/python3 and you run it with ./script), you can choose another interpreter this way:
/bin/python2 -v ../path/to/my/script status
where -v is for the interpreter (if needed), and status is an argument for your script.

as long as the package is on the python path,
add at the end of the script.
if __name__ == "__main__":
call_script()
$ python -m module_name
will run the module e.g
python -m random