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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 get_installed_extjs_apps():
 """ Get all installed extjs apps. :return: List of ``(appdir, module, appname)``. """

    installed_apps = []
    checked = set()
    for app in settings.INSTALLED_APPS:
        if not app.startswith('django.') and not app in checked:
            checked.add(app)
            try:
                installed_apps.append(get_appinfo(app))
            except LookupError, e:
                pass
    return installed_apps