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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 layer(self, layer_name):
 """Get QGIS layer. :param layer_name: The name of the layer to fetch. :type layer_name: str :return: The QGIS layer. :rtype: QgsMapLayer .. versionadded:: 4.0 """

        uri = self.layer_uri(layer_name)
        layer = QgsVectorLayer(uri, layer_name, 'ogr')
        if not layer.isValid():
            layer = QgsRasterLayer(uri, layer_name)
            if not layer.isValid():
                return False

        monkey_patch_keywords(layer)

        return layer