from sets import Set
import string
class KeyedDict(dict):
def __init__(self,keys):
self.__keys = Set(keys)
def __setitem__(self,key,val):
if key not in self.__keys:
keylist = string.join(self.__keys,",")
raise TypeError("Tried to use key '"+key+"'.\nCan only add items with one of the following keys: "+keylist)
return dict.__setitem__(self,key,val)
if __name__ == '__main__':
d = KeyedDict(("fred","barney"))
## these should work
d['fred']='flintstone'
d['barney']='rubble'
## now catch the exception
try:
d['wilma']='flintstone'
except TypeError,e:
print "TypeError correctly thrown"
