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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 post_ext_init(state):
 """Setup blueprint."""

    app = state.app

    app.config.setdefault(
        'OAUTHCLIENT_SITENAME',
        app.config.get('THEME_SITENAME', 'Invenio'))
    app.config.setdefault(
        'OAUTHCLIENT_BASE_TEMPLATE',
        app.config.get('BASE_TEMPLATE',
                       'invenio_oauthclient/base.html'))
    app.config.setdefault(
        'OAUTHCLIENT_COVER_TEMPLATE',
        app.config.get('COVER_TEMPLATE',
                       'invenio_oauthclient/base_cover.html'))
    app.config.setdefault(
        'OAUTHCLIENT_SETTINGS_TEMPLATE',
        app.config.get('SETTINGS_TEMPLATE',
                       'invenio_oauthclient/settings/base.html'))