Virtual Environment

Install :
apt-get update
apt install python3-virtualenv

cd ~
cd VENV
virtualenv
virtualenv-3.6 -p /usr/bin/python36 “virtual env name”
ll or ls -lart
This is going to create a new sandbox
source “virtual env name”/bin/activate  <— this is to active it
which python <—- to see where it is install

pip list  <– package should be almost empty.

The reason behind going virtual for this is to not mix the primary python system and your working environment !

With time you can have different environment and to navigate between them.
deactivate <— to exit an environment
source “name of env”/bin/activate

—— WINDOWS —–

setting the path in windows :
https://www.geeksforgeeks.org/how-to-set-up-command-prompt-for-python-in-windows10/

The venv module provides support for creating lightweight “virtual environments” with their own site directories, optionally isolated from system site directories. Each virtual environment has its own Python binary (which matches the version of the binary that was used to create this environment) and can have its own independent set of installed Python packages in its site directories.

See PEP 405 for more information about Python virtual environments.

Creating virtual environments

Creation of virtual environments is done by executing the command venv:

python3 -m venv /path/to/new/virtual/environment


Running this command creates the target directory (creating any parent directories that don’t exist already) and places a pyvenv.cfg file in it with a home key pointing to the Python installation from which the command was run (a common name for the target directory is .venv). It also creates a bin (or Scripts on Windows) subdirectory containing a copy/symlink of the Python binary/binaries (as appropriate for the platform or arguments used at environment creation time). It also creates an (initially empty) lib/pythonX.Y/site-packages subdirectory (on Windows, this is Lib\site-packages). If an existing directory is specified, it will be re-used.

Deprecated since version 3.6: pyvenv was the recommended tool for creating virtual environments for Python 3.3 and 3.4, and is deprecated in Python 3.6.

Changed in version 3.5: The use of venv is now recommended for creating virtual environments.

On Windows, invoke the venv command as follows:

c:\>c:\Python35\python -m venv c:\path\to\myenv

Then to ACTICATE IT you need to run the command as follow:
"env name"\Scripts\activate.bat

then pip install -r requirements.txt or manual install all modules needed



Alternatively, if you configured the PATH and PATHEXT variables for your Python installation:

c:\>python -m venv c:\path\to\myenv


The command, if run with -h, will show the available options:

usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
ENV_DIR [ENV_DIR ...]

Creates virtual Python environments in one or more target directories.

positional arguments:
ENV_DIR               A directory to create the environment in.

optional arguments:
-h, --help            show this help message and exit
--system-site-packages
Give the virtual environment access to the system
site-packages dir.
--symlinks            Try to use symlinks rather than copies, when symlinks
are not the default for the platform.
--copies              Try to use copies rather than symlinks, even when
symlinks are the default for the platform.
--clear               Delete the contents of the environment directory if it
already exists, before environment creation.
--upgrade             Upgrade the environment directory to use this version
of Python, assuming Python has been upgraded in-place.
--without-pip         Skips installing or upgrading pip in the virtual
environment (pip is bootstrapped by default)
--prompt PROMPT       Provides an alternative prompt prefix for this
environment.
--upgrade-deps        Upgrade core dependencies: pip setuptools to the

Once an environment has been created, you may wish to activate it, e.g. by
sourcing an activate script in its bin directory.


Changed in version 3.9: Add --upgrade-deps option to upgrade pip + setuptools to the latest on PyPI

Changed in version 3.4: Installs pip by default, added the --without-pip and --copies options

Changed in version 3.4: In earlier versions, if the target directory already existed, an error was raised, unless the --clear or --upgrade option was provided.

Note

While symlinks are supported on Windows, they are not recommended. Of particular note is that double-clicking python.exe in File Explorer will resolve the symlink eagerly and ignore the virtual environment.

Note

On Microsoft Windows, it may be required to enable the Activate.ps1 script by setting the execution policy for the user. You can do this by issuing the following PowerShell command:

PS C:> Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser

The created pyvenv.cfg file also includes the include-system-site-packages key, set to true if venv is run with the --system-site-packages option, false otherwise.

Unless the --without-pip option is given, ensurepip will be invoked to bootstrap pip into the virtual environment.

Multiple paths can be given to venv, in which case an identical virtual environment will be created, according to the given options, at each provided path.

Once a virtual environment has been created, it can be “activated” using a script in the virtual environment’s binary directory. The invocation of the script is platform-specific (<venv> must be replaced by the path of the directory containing the virtual environment):

Platform Shell Command to activate virtual environment
POSIX bash/zsh $source <venv>/bin/activate fish$ source <venv>/bin/activate.fish
csh/tcsh $source <venv>/bin/activate.csh PowerShell Core$ <venv>/bin/Activate.ps1
Windows cmd.exe C:\> <venv>\Scripts\activate.bat
PowerShell PS C:\> <venv>\Scripts\Activate.ps1

When a virtual environment is active, the VIRTUAL_ENV environment variable is set to the path of the virtual environment. This can be used to check if one is running inside a virtual environment.

You don’t specifically need to activate an environment; activation just prepends the virtual environment’s binary directory to your path, so that “python” invokes the virtual environment’s Python interpreter and you can run installed scripts without having to use their full path. However, all scripts installed in a virtual environment should be runnable without activating it, and run with the virtual environment’s Python automatically.

You can deactivate a virtual environment by typing “deactivate” in your shell. The exact mechanism is platform-specific and is an internal implementation detail (typically a script or shell function will be used).

New in version 3.4: fish and csh activation scripts.

New in version 3.8: PowerShell activation scripts installed under POSIX for PowerShell Core support.

Note

A virtual environment is a Python environment such that the Python interpreter, libraries and scripts installed into it are isolated from those installed in other virtual environments, and (by default) any libraries installed in a “system” Python, i.e., one which is installed as part of your operating system.

A virtual environment is a directory tree which contains Python executable files and other files which indicate that it is a virtual environment.

Common installation tools such as setuptools and pip work as expected with virtual environments. In other words, when a virtual environment is active, they install Python packages into the virtual environment without needing to be told to do so explicitly.

When a virtual environment is active (i.e., the virtual environment’s Python interpreter is running), the attributes sys.prefix and sys.exec_prefix point to the base directory of the virtual environment, whereas sys.base_prefix and sys.base_exec_prefix point to the non-virtual environment Python installation which was used to create the virtual environment. If a virtual environment is not active, then sys.prefix is the same as sys.base_prefix and sys.exec_prefix is the same as sys.base_exec_prefix (they all point to a non-virtual environment Python installation).

When a virtual environment is active, any options that change the installation path will be ignored from all distutils configuration files to prevent projects being inadvertently installed outside of the virtual environment.

When working in a command shell, users can make a virtual environment active by running an activate script in the virtual environment’s executables directory (the precise filename and command to use the file is shell-dependent), which prepends the virtual environment’s directory for executables to the PATH environment variable for the running shell. There should be no need in other circumstances to activate a virtual environment; scripts installed into virtual environments have a “shebang” line which points to the virtual environment’s Python interpreter. This means that the script will run with that interpreter regardless of the value of PATH. On Windows, “shebang” line processing is supported if you have the Python Launcher for Windows installed (this was added to Python in 3.3 – see PEP 397 for more details). Thus, double-clicking an installed script in a Windows Explorer window should run the script with the correct interpreter without there needing to be any reference to its virtual environment in PATH.