Installer details

The installers pynsist builds do a number of things:

  1. Install a number of files in the installation directory the user selects:
    • An embedded build of Python, including the standard library.
    • A copy of the necessary Microsoft C runtime for Python to run, if this is not already installed on the system.
    • The launcher script(s) that start your application
    • The icon(s) for your application launchers
    • Python packages your application needs
    • Any other files you specified
  2. Create a start menu shortcut for each launcher script. If there is only one launcher, it will go in the top level of the start menu. If there’s more than one, the installer will make a folder named after the application.
  3. If you have specified any commands, modify the PATH environment variable in the registry, so that your commands will be available in a system command prompt.
  4. Byte-compile all Python files in the pkgs subdirectory. This should slightly improve the startup time of your application.
  5. Write an uninstaller, and the registry keys to put it in ‘Add/remove programs’.

The installer (and uninstaller) is produced using NSIS, with the Modern UI.

Logging output

When your installed application is run in GUI mode (without a console), any output from print() (and anything else that writes to stdout or stderr from Python) will be written to a file %APPDATA%\scriptname.log. On Windows 7, APPDATA defaults to C:\Users{username}\AppData\Roaming.

This file is recreated each time your application is launched, so it shouldn’t keep growing larger.

You can override this by setting sys.stdout and sys.stderr.

Uncaught exceptions

If there is an uncaught exception in your application - for instance if it fails to start because a package is missing - the traceback will be written to the same log file described in Logging output. If users report crashes, details of the problem will probably be found there.

You can override this by setting sys.excepthook().

This is only provided if you specify your application using entry_point.

You can also debug an installed application by using the installed Python to launch the application. This will show tracebacks in the Command Prompt. In the installation directory run:

C:\\Program Files\\Application>Python\\python.exe "Application.launch.pyw"

Working directory

If users start your application from the start menu shortcuts, the working directory will be set to their home directory (%HOMEDRIVE%%HOMEPATH%). If they double-click on the scripts in the installation directory, the working directory will be the installation directory. Your application shouldn’t rely on having a particular working directory; if it does, use os.chdir() to set it first.