qt.py 文件源码

def _init():
    """Try loading each binding in turn

    Please note: the entire Qt module is replaced with this code:
        sys.modules["Qt"] = binding()

    This means no functions or variables can be called after
    this has executed.

    """

    preferred = os.getenv("QT_PREFERRED_BINDING")
    verbose = os.getenv("QT_VERBOSE") is not None
    bindings = (_pyside2, _pyqt5, _pyside, _pyqt4)

    if preferred:

        # Internal flag (used in installer)
        if preferred == "None":
            sys.modules[__name__].__wrapper_version__ = __version__
            return

        preferred = preferred.split(os.pathsep)
        available = {
            "PySide2": _pyside2,
            "PyQt5": _pyqt5,
            "PySide": _pyside,
            "PyQt4": _pyqt4
        }

        try:
            bindings = [available[binding] for binding in preferred]
        except KeyError:
            raise ImportError(
                "Available preferred Qt bindings: "
                "\n".join(preferred)
            )

    for binding in bindings:
        _log("Trying %s" % binding.__name__[1:], verbose)

        try:
            sys.modules[__name__] = binding()
            return

        except ImportError as e:
            _log(" - ImportError(\"%s\")\n" % e, verbose)

            continue

    # If not binding were found, throw this error
    raise ImportError("No Qt binding were found.")