Apologies for naive question - I'm brand new to python & web2py.

Trying to display a list of tables in a form, IF a criteria are met. I have code working; assay_display is shown in a field. 

def assay_display(row):
    assay_list = list()
    if db(row.MML.lot == db.amino_acid.lot).select():
        assay_list.append('Amino Acid')
    assay_string = "<br />".join(assay_list)
    return XML(assay_string)

But now instead of merely listing the name of the table, I'd like to create a link to a url. 

Can someone point me to an example, or a place to start? I've ready the Web2py book, chapter 4, but am too new to have much of it be clear. 

Thank you in advance-

Adrienne