Source

File: wp-includes/functions.wp-scripts.php

function wp_print_scripts( $handles = false ) {
	global $wp_scripts;

	/**
	 * Fires before scripts in the $handles queue are printed.
	 *
	 * @since 2.1.0
	 */
	do_action( 'wp_print_scripts' );

	if ( '' === $handles ) { // For 'wp_head'.
		$handles = false;
	}

	_wp_scripts_maybe_doing_it_wrong( __FUNCTION__ );

	if ( ! ( $wp_scripts instanceof WP_Scripts ) ) {
		if ( ! $handles ) {
			return array(); // No need to instantiate if nothing is there.
		}
	}

	return wp_scripts()->do_items( $handles );
}