If this was PHP, I would probably do something like this:
function no_more_half_widths($string){
$foo = array(\'1\',\'2\',\'3\',\'4\',\'5\',\'6\',\'7\',\'8
The built-in unicodedata module can do it:
>>> import unicodedata
>>> foo = u'1234567890'
>>> unicodedata.normalize('NFKC', foo)
u'1234567890'
The “NFKC” stands for “Normalization Form KC [Compatibility Decomposition, followed by Canonical Composition]”, and replaces full-width characters by half-width ones, which are Unicode equivalent.
Note that it also normalizes all sorts of other things at the same time, like separate accent marks and Roman numeral symbols.