At a client I had to review the code of a new Python project. I cloned the repo, used conda to create a virtualenv and finally let Poetry install all Python dependencies. This went without a hitch but after the installation of the dependencies, each subsequent Poetry command would show me an error dialog like this:
(my-venv) C:\Users\Pieter\repos\my-venv>poetry cache list --help
So each Poetry command triggered a failing search for a specific procedure in a DLL in my base conda environment. Some googling (and trial & error) lead me to this section of the README of the pywin32 package:
A very common report is that people install pywin32, but many imports fail with errors similar to [The specified procedure could not be found / Entry-point not found Errors?].
In almost all cases, this tends to mean there are other pywin32 DLLs installed in your system, but in a different location than the new ones. This sometimes happens in environments that come with pywin32 pre-shipped (eg, anaconda?).
Indeed, this could describe the issue I encountered: pywin32 is one of the dependencies installed, pythoncom39.dll is a pywin32 DLL and I’m working in a conda virtualenv.
The README starts with telling you that pywin32 has a postinstall step, that you have to execute manually. It doesn’t tell you why that step is necessary but it restates the advise after the quoted section. So here it goes:
(my-venv) C:\Users\Pieter\repos\my-venv>cd C:\Users\Pieter\Miniconda3\envs\my-venv\Scripts (my-venv) C:\Users\Pieter\Miniconda3\envs\my-venv\Scripts>python pywin32_postinstall.py -install Parsed arguments are: Namespace(install=True, remove=False, wait=None, silent=False, quiet=False, destination='C:\\Users\\Pieter\\Miniconda3\\envs\\my-venv\\Lib\\site-packages') Copied pythoncom39.dll to C:\Users\Pieter\Miniconda3\envs\my-venv\pythoncom39.dll Copied pywintypes39.dll to C:\Users\Pieter\Miniconda3\envs\my-venv\pywintypes39.dll You do not have the permissions to install COM objects. The sample COM objects were not registered. -> Software\Python\PythonCore\3.9\Help[None]=None -> Software\Python\PythonCore\3.9\Help\Pythonwin Reference[None]='C:\\Users\\Pieter\\Miniconda3\\envs\\my-venv\\Lib\\site-packages\\PyWin32.chm' Pythonwin has been registered in context menu Creating directory C:\Users\Pieter\Miniconda3\envs\my-venv\Lib\site-packages\win32com\gen_py Can't install shortcuts - 'C:\\Users\\Pieter\\AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Python 3.9' is not a folder The pywin32 extensions were successfully installed. (my-venv) C:\Users\Pieter\Miniconda3\envs\my-venv\Scripts>
So when you install pywin32, apparently the pywin32 DLLs aren’t installed in a location where Python, or a tool that relies on it such as Poetry, can find them. The postinstall step copies them to a directory that does allow them to be found. And indeed, after I executed this step, the Poetry commands didn’t result in the error dialog anymore.