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Python CWMS Portable Environment

A portable Windows CPython 3.13 environment with CWMS libraries and their dependencies already installed.

Install

The first release that supports the Windows installer is v2.0. Release v1.11 cannot be installed this way because it has no detached signature asset; a new signed v2.0 release must be published first. Do not modify the historical v1.11 release.

  1. Open the latest release.
  2. Download PythonCWMS-Installer.zip.
  3. Extract the installer ZIP. It creates a PythonCWMS-Installer folder.
  4. Open that folder and double-click Install-PythonCWMS.cmd.

After a successful installation, the installer removes PythonCWMS-Installer.zip and its extracted folder when possible.

The installer downloads the signed portable environment, verifies its SHA-256 hash and RSA signature, safely extracts it, and runs Python before changing an existing installation.

The default installation directory is:

C:\hec\python\pythonCWMS

WinPython recommends keeping its base directory path to about 37 characters or fewer. The installer warns when a custom -InstallRoot exceeds that recommendation.

To select another directory, open Command Prompt in the extracted installer directory and run:

Install-PythonCWMS.cmd -InstallRoot "D:\Tools\pythonCWMS"

Upgrade and backups

If the target directory already exists, the installer asks whether to replace it and defaults to Yes. The existing installation is retained as a timestamped backup. For an unattended upgrade, use -Force to approve replacement without prompting:

Install-PythonCWMS.cmd -Force

After confirmation (or -Force), the installer renames the exact existing target to a timestamped sibling such as pythonCWMS.backup-20261005-143000. If installation fails, it restores that backup. After a successful installation the backup is retained and must be removed manually when no longer needed.

Environment variables

The installer uses .NET user-environment APIs to set:

  • PYTHON_CWMS_HOME to <InstallRoot>\python
  • user PATH entries %PYTHON_CWMS_HOME% and %PYTHON_CWMS_HOME%\Scripts

The PATH update is idempotent and removes entries from older Python CWMS installations. Close all Command Prompt, PowerShell, Windows Terminal, and VS Code windows after installation, then open a new terminal and run pythonCWMS --version.

For VS Code, set:

"python.defaultInterpreterPath": "${env:PYTHON_CWMS_HOME}\\python.exe"

If a workspace has retained another interpreter, run Python: Clear Workspace Interpreter Setting from the Command Palette.

Install additional libraries

Run packages through the installed interpreter:

pythonCWMS -m pip install package-name

Packages included in releases are defined by base requirements and supplemental requirements, then resolved into the hash-pinned Windows lock.

RTS and HEC-DSS scripts

Jython is still used as a launcher inside RTS and HEC-DSS. Edit python_script_path and args in example_python_script_launcher.py. Set args to None or an empty string when no arguments are needed; multiple arguments are split before launching CPython.

Do not use the former Jython install_python.py workflow to install Python CWMS. The file remains as a compatibility notice for old bookmarks, while the signed Windows installer is documented in the Jython migration guide. Saved copies of the old installer are also stopped by the retirement document at the root of main.

See CONTRIBUTING.md for release maintenance.