Removing a subset of a dict from within a list

a = {1:'', 2:'', 3:'', 4:''}
exclusion = [3, 4, 5]

# have to build up a new list or the iteration breaks
toRemove = []
for var in a.iterkeys():
    if var in exclusion:
        toRemove.append(var)

for var in toRemove:
    del a[var]

for key in exclusion:
     a.pop(key, None)

a = dict((key,value) for (key,value) in a.iteritems() if key not in exclusion)

exclusion = set([3, 4, 5])

for key in exclusion.intersection(a):
    del a[key]