title: Retrieve input value from form in html and use it in flask
body: <p>So, I need to grab an input value from an html form and use it in flask.  Here's an example  of python and html for reference:</p>
  
  <p>python:</p>
  
  <pre><code>@app.route("/post_field", methods=["GET", "POST"])
  
  def need_input():
  
      for key in request.form["post_field"]:    
  
          if key == "value1":
              #do the thing I want#
  </code></pre>
  
  <p>html:</p>
  
  <pre><code>&lt;form action="/post_field" method="post"&gt;
      &lt;input type="hidden" name="this_name" value="value1" /&gt;
      &lt;input type="submit" value="Press Me!"/&gt;
  &lt;/form&gt; 
  </code></pre>
  
  <p>I get a 400 error when I click that Press Me input.</p>