Using PythonService.exe to host python service whi

Question

I've got a Windows 7 environment where I need to develop a Python Windows Service using Python 3.4. I'm using pywin32's win32service module to setup the service and most of the hooks seem to be working ok.

The problem is when I attempt to run the service from source code (using python service.py install followed by python service.py start). This uses PythonService.exe to host service.py - but I'm using a venv virtual environment and the script can't find it's modules (error message discovered with python service.py debug).

Pywin32 is installed in the virtualenv and in looking at the source code of PythonService.exe, it dynamically links in Python34.dll, imports my service.py and invokes it.

How can I get PythonService.exe to use my virtualenv when running my service.py?

Answer 1

It appears this used to work correctly with the virtualenv module before virtual environments were added to Python 3.3. There's anecdotal evidence (see this answer: https://stackoverflow.com/a/12424980/1055722) that Python's site.py used to look upward from the executable file until it found a directory that would satisfy imports. It would then use that for sys.prefix and this was sufficient for PythonService.exe to find the virtualenv it was inside of and use it.

If that was the behavior, it appears that site.py no longer does that with the introduction of the venv module. Instead, it looks one level up for a pyvenv.cfg file and configures for a virtual environment in that case only. This of course doesn't work for PythonService.exe which is buried down in the pywin32 module under site-packages.

To work around it, I adapted the activate_this.py code that comes with the original virtualenv module (see this answer: https://stackoverflow.com/a/33637378/1055722). It is used to bootstrap an interpreter embedded in an executable (which is the case with PythonService.exe) into using a virtualenv. Unfortunately, venv does not include this.

Here's what worked for me. Note, this assumes the virtual environment is named my-venv and is located one level above the source code location.

import os
import sys

if sys.executable.endswith("PythonService.exe"):

    # Change current working directory from PythonService.exe location to something better.
    service_directory = os.path.dirname(__file__)
    source_directory = os.path.abspath(os.path.join(service_directory, ".."))
    os.chdir(source_directory)
    sys.path.append(".")

    # Adapted from virtualenv's activate_this.py
    # Manually activate a virtual environment inside an already initialized interpreter.
    old_os_path = os.environ['PATH']
    venv_base = os.path.abspath(os.path.join(source_directory, "..", "my-venv"))
    os.environ['PATH'] = os.path.join(venv_base, "Scripts") + os.pathsep + old_os_path
    site_packages = os.path.join(venv_base, 'Lib', 'site-packages')
    prev_sys_path = list(sys.path)
    import site
    site.addsitedir(site_packages)
    sys.real_prefix = sys.prefix
    sys.prefix = venv_base

    new_sys_path = []
    for item in list(sys.path):
        if item not in prev_sys_path:
            new_sys_path.append(item)
            sys.path.remove(item)
    sys.path[:0] = new_sys_path

One other factor in my troubles - there is a new pypi wheel for pywin32 that is provided by the Twisted folks that makes it easier to install with pip. The PythonService.exe in that package was acting oddly (couldn't find a pywin32 dll when invoked) compared to the one you get when installing the official win32 exe package into the virtual env using easy_install.

Answer 2

Thanks very much for posting this question and a solution. I took a slightly different approach which might also be useful. It is pretty difficult to find working tips for Python services, let alone doing it with a virtualenv. Anyway...

Steps

This is using Windows 7 x64, Python 3.5.1 x64, pywin32-220 (or pypiwin32-219).

• Open an Administrator command prompt.
• Create a virtualenv. C:\Python35\python -m venv myvenv
• Activate the virtualenv. call myvenv\scripts\activate.bat
• Install pywin32, either:
  • From Pypi: pip install pypiwin32,
  • From http://www.lfd.uci.edu/~gohlke/pythonlibs/: pip install path\to\pywin32.whl
• Run the post-install script python myvenv\Scripts\pywin32_postinstall.py -install.
  • This script registers the DLL's in the system, and copies them to C:\Windows\System32. The DLL's are named pythoncom35.dll and pywintypes35.dll. So virtual environments on the same machine on the same major Python point release will share these... it's a minor tradeoff :)
• Copy myvenv\Lib\site-packages\win32\pythonservice.exe to myvenv\Scripts\pythonservice.exe
  • On the service class (whatever subclasses win32serviceutil.ServiceFramework), set the class property _exe_path_ to point to this relocated exe. This will become the service binPath. For example: _exe_path_ = os.path.join(*[os.environ['VIRTUAL_ENV'], 'Scripts', 'pythonservice.exe']).

Discussion

I think why this works is that Python looks upwards to figure out where the Libs folders are and based on that sets package import paths, similar to the accepted answer. When pythonservice.exe is in the original location, that doesn't seem to work smoothly.

It also resolves DLL linking problems (discoverable with depends.exe from http://www.dependencywalker.com/). Without the DLL business sorted out, it won't be possible to import from the *.pyd files from venv\Lib\site-packages\win32 as modules in your scripts. For example it's needed allow import servicemanager; as servicemanager.pyd is not in the package as a .py file, and has some cool Windows Event Log capabilities.

One of the problems I had with the accepted answer is that I couldn't figure out how to get it to accurately pick up on package.egg-link paths that are created when using setup.py develop. These .egg-link files include the path to the package when it's not located in the virtualenv under myvenv\Lib\site-packages.

If it all went smoothly, it should be possible to install, start and test the example win32 service (from an Admin prompt in the activated virtualenv):

python venv\Lib\site-packages\win32\Demos\service\pipeTestService.py install
python venv\Lib\site-packages\win32\Demos\service\pipeTestService.py start
python venv\Lib\site-packages\win32\Demos\service\pipeTestServiceClient.py

The Service Environment

Another important note in all this is that the service will execute the python code in a completely separate environment to the one you might run python myservice.py debug. So for example os.environ['VIRTUAL_ENV'] will be empty when running the service. This can be handled by either:

• Setting environment variables from inside the script, e.g.
  • Find current path starting from the sys.executable, as described in the accepted answer.
  • Use that path to locate a config file.
  • Read the config file and put them in the environment with os.environ.
• Add registry keys to the service with the environment variables.
  • See Accessing Environment Variables from Windows Services for doing this manually with regedit.exe
  • See REG ADD a REG_MULTI_SZ Multi-Line Registry Value for doing this from the command line.

Answer 3

For anyone reading in 2018, I didn't have any luck with either solution above (Win10, Python 3.6) - so this is what I did to get it working. The working directory is in site-packages/win32 on launch, so you need to change the working directory and fix the sys.path before you try and import any project code. This assumed venv sits in your project dir, otherwise you may just need to hard code some paths:

import sys
import os
if sys.executable.lower().endswith("pythonservice.exe"):
    for i in range(4): # goes up 4 directories to project folder
        os.chdir("..")        
    # insert site-packages 2nd in path (behind project folder)
    sys.path.insert(1, os.path.join("venv",'Lib','site-packages'))

[REST OF IMPORTS]
class TestService(win32serviceutil.ServiceFramework):
    [...]