Function to check if the current page is a post edit page

is_edit_page.php

<?php
/**
 * is_edit_page 
 * function to check if the current page is a post edit page
 * 
 * @author Ohad Raz <[email protected]>
 * @url https://wordpress.stackexchange.com/questions/50043
 * 
 * @param  string  $new_edit what page to check for accepts new - new post page ,edit - edit post page, null for either
 * @return boolean
 */
function is_edit_page($new_edit = null){
    global $pagenow;
    //make sure we are on the backend
    if (!is_admin()) return false;


    if($new_edit == "edit")
        return in_array( $pagenow, array( 'post.php',  ) );
    elseif($new_edit == "new") //check for new post page
        return in_array( $pagenow, array( 'post-new.php' ) );
    else //check for either new or edit
        return in_array( $pagenow, array( 'post.php', 'post-new.php' ) );
}