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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def loaded_api():
 """Return which API is loaded, if any If this returns anything besides None, importing any other Qt binding is unsafe. Returns ------- None, 'pyside', 'pyqt', or 'pyqtv1' """

    if 'PyQt4.QtCore' in sys.modules:
        if qtapi_version() == 2:
            return QT_API_PYQT
        else:
            return QT_API_PYQTv1
    elif 'PySide.QtCore' in sys.modules:
        return QT_API_PYSIDE
    elif 'PyQt5.QtCore' in sys.modules:
        return QT_API_PYQT5
    return None