[web2py] Drop-down with "Other (fill in text)" option?

[Alec Taylor]

Given a simple table like:

db.define_table(
    'foo',
    Field('bar', requires=IS_IN_SET([1,2,3,4,'fzr',6,7,8,9, 'Other'])

    # If other is picked, display text-box with IS_ALPHANUMERIC validator)


How do I add this option? - I'm guessing it would be solved best using 
SQLFORM.factory.

Thanks for all suggestions,

Alec Taylor

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