通过环境变量指定pyqtgraph的Qt库

pyqtgraph/Qt/__init__.py中会自动设置pyqtgraph使用的Qt库

PYSIDE = 'PySide'
PYSIDE2 = 'PySide2'
PYSIDE6 = 'PySide6'
PYQT4 = 'PyQt4'
PYQT5 = 'PyQt5'
PYQT6 = 'PyQt6'

QT_LIB = os.getenv('PYQTGRAPH_QT_LIB')

if QT_LIB is not None:
    try:
        __import__(QT_LIB)
    except ModuleNotFoundError:
        raise ModuleNotFoundError(f"Environment variable PYQTGRAPH_QT_LIB is set to '{os.getenv('PYQTGRAPH_QT_LIB')}', but no module with this name was found.")

## Automatically determine which Qt package to use (unless specified by
## environment variable).
## This is done by first checking to see whether one of the libraries
## is already imported. If not, then attempt to import in the order
## specified in libOrder.
if QT_LIB is None:
    libOrder = [PYQT6, PYSIDE6, PYQT5, PYSIDE2]

    for lib in libOrder:
        if lib in sys.modules:
            Q