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For most Python engineering projects, create one isolated environment in the repository’s .venv folder, install dependencies using the project’s existing instructions, and confirm that your shell is using that environment’s interpreter. Use the Python version and dependency workflow specified by the project or its CI configuration; a generic setup guide cannot determine which versions suit every repository.
Before you begin: check the project’s Python and dependency requirements
If you are joining an existing repository, first read its README and setup documentation, then check its Python version declaration, dependency files, and CI configuration. These determine the supported interpreter and how the team expects packages to be installed. Do not choose the newest Python version automatically: dependencies or project code may support a narrower range.
The Python Packaging User Guide describes its instructions as applying to supported Python versions 3.8 and later. That describes the guide’s scope; it does not mean every project supports every version in that range. Python Packaging User Guide
For a new project with no existing policy, choose an interpreter version compatible with the libraries and tools you plan to use, and record that choice in the project’s setup instructions.
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Create a project environment with venv
Python’s standard-library venv module creates an environment with its own package installation area. Keeping it in a .venv directory at the repository root makes it easy to identify and configure in common editors. Run the command from that root directory, using the interpreter version selected for the project.
Unix and macOS
python3 -m venv .venvWindows
py -m venv .venvThe Windows py launcher selects an installed Python interpreter. If the repository requires a particular version and multiple versions are installed, select the required interpreter explicitly using the launcher’s version-selection syntax, or use that interpreter’s executable to create the environment.
By default, venv bootstraps pip into the environment. Since Python 3.12, setuptools is no longer a core dependency of a venv, so do not add a universal setuptools installation step unless this project needs it. Python documentation: Installing Python modules
Activate the environment in your shell
Activation adjusts the current shell’s PATH so that commands such as python and pip resolve to the environment. The activation command depends on the operating system and shell.
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source .venv/bin/activateWindows Command Prompt
.venvScriptsactivateWindows PowerShell
.venvScriptsActivate.ps1PowerShell’s execution policy may prevent script activation in some configurations. Follow your organization’s policy or Microsoft’s recommended approach rather than weakening a machine-wide setting just to activate a project environment. The Python Packaging User Guide documents activation commands for common platforms. Python Packaging User Guide
Verify that the right Python is active
Before installing packages or running project commands, check the resolved interpreter path. It should point into this repository’s .venv, not a system-wide Python or another project’s environment.
Unix and macOS
which pythonWindows
where pythonAfter activation, the first resolved path should be inside the project’s .venv directory. If it is not, activate the environment in the shell where you intend to work, or invoke its interpreter directly: .venv/bin/python on Unix/macOS or .venvScriptspython.exe on Windows. Activation is convenient, but not required; using the interpreter’s full path avoids relying on shell activation. Python Packaging User Guide Python documentation: venv
Install the dependencies the project declares
Use the repository’s documented dependency workflow. If it uses a requirements.txt file, install from the active environment with:
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python -m pip install -r requirements.txtUsing python -m pip ties pip to the interpreter selected by python, reducing the risk of installing packages into a different Python than the one running your project. The command above is appropriate only when the repository actually uses that file. If it specifies another dependency manager, lock file, or setup command, follow that convention instead; there is no single lock-file standard established by the cited setup guidance.
For an existing engineering project, do not invent a dependency file or add packages merely to complete a generic checklist. Native extensions can also require operating-system libraries or build tools, but those requirements are project-specific; install them only when the project documents them.
Make the setup reproducible for teammates
Commit the project’s approved dependency inputs and setup metadata, not the environment itself. Add .venv/ to the repository’s ignore rules if it is not already ignored. A teammate or CI job should be able to create a fresh environment and install from the committed project instructions.
Virtual environments are generally not portable: installed scripts can contain absolute paths to the environment’s interpreter. If you move or rename the repository, or work from a new checkout, recreate the environment in its new location rather than copying or moving the old .venv. Keep source files outside the environment directory. Python documentation: venv
Configure your editor to use the same interpreter
Set the editor’s project interpreter to the Python executable inside .venv. Then verify that the editor’s integrated terminal, test runner, and any project tasks use that same interpreter. Otherwise, code can appear to import correctly in one context but fail in another because the editor is using a different environment.
Common setup problems and fixes
The shell still finds system Python
Run the activation command for your actual shell, then check which python or where python again. If activation is unavailable or undesirable, call the environment’s interpreter by its full path and use it to run pip.
PowerShell refuses to run the activation script
This is an execution-policy issue, not evidence that the environment failed to be created. Use an activation method permitted by your organization, or skip activation and run .venvScriptspython.exe directly.
A package installation fails while building a native extension
The environment isolates Python packages; it does not supply every operating-system compiler, library, or header a package may need. Check the project’s installation instructions for the required system dependencies rather than guessing which tools to add.
The project stopped working after the folder was moved
Because environments can contain scripts tied to their original absolute interpreter path, remove and recreate .venv at the new location, then reinstall dependencies using the project’s declared workflow.
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