Source: python – Unable to load QMYSQL Driver on PySide2 – Stack Overflow
P.S. almost half of this info is officially published at https://doc.qt.io/qt-6/deployment-plugins.html
I use PySide6 on Windows 10 and %QT_SQL_DRIVER_PATH% does not work for me. What works for PySide6 is the %QT_PLUGIN_PATH% environment variable.
Let’s assume that you have built (or downloaded) a SQL driver for Qt platform into C:\projects\my-project-1\qt-plugins\sqldrivers, so that there is qsqlmysql.dll there.
CASE #1: you execute QSqlDatabase.addDatabase("QMYSQL"), but you get the following error:
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QODBC QPSQL
It means that qsqlmysql.dll (a plugin for Qt platform) was not found.
The fix is to define the environment variable %QT_PLUGIN_PATH% and put qsqlmysql.dll into %QT_PLUGIN_PATH%/sqldrivers/. You can even do it in your Python script before invocation of QSqlDatabase.addDatabase:
os.environ['QT_PLUGIN_PATH'] = r'C:\projects\my-project-1\qt-plugins'
Note, qsqlmysql.dll must be a release version built using MSVC (64-bit since it is year 2022), not MinGW. Debug version fails by some reason in my experience.
If you don’t want to define the %QT_PLUGIN_PATH% environment variable, an alternative fix is to copy qsqlmysql.dll into one of these directories: <python-install-dir>/sqldrivers/ or <python-install-dir>/lib/site-packages/PySide6/plugins/sqldrivers/.
Another alternative is to use QCoreApplication.addLibraryPath like this:
app = QCoreApplication(sys.argv)
app.addLibraryPath(r'C:\projects\my-project-1\qt-plugins')
And yet another alternative is to create <python-install-dir>\qt.conf or <python-install-dir>\qt6.conf with following content:
[Paths]
Prefix=C:/projects/my-project-1
Plugins=qt-plugins
or even so:
[Paths]
Plugins=C:/projects/my-project-1/qt-plugins
N.B. qt6.conf is ignored if qt.conf doesn’t exist. If you use qt6.conf, you must create an empty qt.conf at least.
CASE #2: you execute QSqlDatabase.addDatabase("QMYSQL"), but you get the following error:
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QMARIADB QMYSQL QSQLITE QODBC QPSQL
It means that qsqlmysql.dll was found, but its dependencies were not. The qsqlmysql.dll additionally requires 3 DLLs: libmysql.dll, libcrypto-1_1-x64.dll, libssl-1_1-x64.dll. These DLLs must be located in %PATH% or in current directory.
N.B. if you place the DLLs near your python script, this won’t work if current working directory is different from scripts’s location. But you can modify %PATH% even in your Python script. For example, if you copied said DLLs into deps sub-directory of your project:
os.environ["PATH"] += os.pathsep + os.path.join(os.path.dirname(__file__), 'deps')
Another possible issues might be:
- architecture mismatch (some DLLs are 64-bit, while others are 32-bit).
- binary incompatibility – e.g. if “sqldrivers/qsqlmysql.dll” is built with MinGW or it’s a debug version downloaded from https://github.com/thecodemonkey86/
Define the environment variable: set QT_DEBUG_PLUGINS=1 – this might help to troubleshoot such issues.
