Python Requests Onclick

I've successfully logged into a website and loaded a table that can then be downloaded as an .xls file. The issue I'm having is that an image has to be clicked to call the download. I haven't figured out how to post the correct data to fetch the .xls file.

Here is the website's HTML:

 <table border="0" width ="95%" align ="center">
    <tr>
        <form name="downloadXLSForm" method="POST" action="/control/filedownload">
            <input type="hidden" name="fileType" value="mlInventory">
            <td align="left" valign = "top">
                <font face="Verdana, Arial, Helvetica, sans-serif" size="-2">
                    <input type="image" src="../images/excel_download.jpg" onClick="document.downloadXLSForm.submit()" value="Excel Download" Alt="Download the results above into MS Excel">
                </font>
            </td>
        </form>         
        <td align="right" valign = "top">
            <form name="mlInventorysearch" method="post" action="/control/mlinventorysearch">
                <input type="hidden" name="refreshSearch" value="true">
                <input type="submit" value="New Search">
            </form>
        </td>
    </tr>
  </table>

There is a link embedded in the website that points to https://www.emlco.com/control/filedownload but when I try and get it, the page is empty.

Here is my code:

with requests.Session() as z:
    z.get("https://www.emlco.com/control/j_security_check", stream=True)
    p3 = z.post("https://www.emlco.com/control/j_security_check",data=payload3) 
    z.get(link)
    inventory_start = z.post(link, data={'newSearch':'true'})
    inventory_excel = z.post(link,data={'fileType':'mlInventory'})
    #inventory_excel = z.post('https://www.emlco.com/control/filedownload',data={'fileType':'mlInventory'})
    inventory_excel = z.get('https://www.emlco.com/control/filedownload', stream = True)
    #output = open('MLCStock.xls', 'wb')
    #output.write(inventory_excel.content)
    #output.close()

    print(inventory_excel.url)
    print(inventory_start.url)
    print("Done")

I apologize for the redundant comments. I was trying various combinations to see what would take.

Thanks in advance. I am quite new at Python.