It some what depends on your definition of whitespace. I would generally call whitespace to be spaces, tabs, line breaks and carriage returns. If this is your definition you want to use a regex with \s to replace all whitespace charactors:
import re
def myCleaner(foo):
print 'dirty: ', foo
foo = re.sub(r'\s', '', foo)
foo = foo[:-3]
foo = foo.upper()
print 'clean:', foo
print
myCleaner("BS1 1AB")
myCleaner("bs11ab")
myCleaner("BS111ab")