How to select a Radio Button?

I am using mechanize and I am trying to select a button from a radio button list. This list has 5 items. How can I select the first item? Docs didn't help me.

>>> br.form
<ClientForm.HTMLForm instance at 0x9ac0d4c>
>>> print(br.form)
<form1 POST http://www.example.com application/x-www-form-urlencoded
<HiddenControl(DD=17010200) (readonly)>
<RadioControl(prodclass=[1, 2, 3, 4, 5])>
<SubmitControl开发者_运维百科(submit=text) (readonly)>>

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It should be as simple as

br.form['prodclass'] = ['1']

I prefer the more verbose:

br.form.set_value(['1'],name='prodclass')