$def with (error_msg=None, url=None, short_url=None)
<h1>Enter the URL you want to shorten below</h1>
<div id="url_input_div">
    <form method="post" action="/" id="url_input_form">
        <label for="url" id="in">URL:</label>
        <input type="text" id="url" class="url_text" value="" name="url"></input>
        <input type="submit" id="submit_button" value="Generate URL"></input>
    </form>
    
    $if url:
        <div id="short_url_info">
            <label for="out">Short URL:</label>
            <input type="text" name="out" class="url_text" value="$short_url"></input>
            <p>Original URL: $url</p>
        </div>
    $if error_msg:
        <div id="short_url_info">
            <p class="error">$error_msg</p>
        </div>
</div>