DLL load failed when importing PyQt5

If you created a virtualenv, check if python3.dll was copied into the Scripts directory of that virtualenv. Chances are only python35.dll (or python36.dll, etc., depending on the Python version) was copied, in which case you would get the error you're getting.

It is because of missing Python3.dll (stub dll, that re-exports Python3x.dll functions, so that one version of extension can work for multiple versions of python).

If your Python distro doesn't bundle python3.dll, you can try one from WinPython (https://winpython.github.io/).

At least the 2017/04/01 versions should have it.

1) Download WinPython ('Zero' version suffices; must be same "main version" - 3.5/3.6 -and "bitness" - 32/64 - as your Python !!!).

2) Extract to some temp directory, take the python3.dll and stick it into your python dir, next to the python3x.dll.

3) Enjoy working QT

I know the topic is old but I have also had this problem with the newest version of PyQT 5.11 but I've downgraded it to 5.9 via:

pip install PyQT5==5.9

and it has solved the issue.

In my case, I had Windows 10 32-bits and Python 3.7.2. Using PyQt5 5.11 installed via pip I got this error:

from PyQt5.QtWidgets import QApplication
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: DLL load failed: The specified module could not be found.

I noticed that version 5.11 came without Qt DLLs, so I reinstalled an earler version with python -m pip uninstall PyQt5 and python -m pip install PyQt5==5.10

Never use --no-cache-dir since it will produce an assert error when installing the whl file:

assert building_is_possible
assertion Error

I ended up installing 5.10 and had the following error:

qt.qpa.plugin: Could not load the Qt platform plugin "windows" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

After setting QT_DEBUG_PLUGINS and even plugin path with:

set QT_DEBUG_PLUGINS=
set QT_PLUGIN_PATH=C:\Python37-32\Lib\site-packages\PyQt5\Qt\plugins

I realised that the dll qwindows.dll was searched in the right path where it resides.

TL;DR: I re-ran my python Qt script with UAC elevation, and guess what, it worked !