human
Solve the following python programming problem given the following code:
@ classmethod 
def update_assignments(cls, new_assignments) : 
    "
        Atomically update the set of country assignments in a transaction.

        For each assignment in the updated list, either update the existing
        one (and delete its delegates), or create a new one if it doesn't
        exist.
        " 
    assignments = cls.objects.all ().values () 
    assignment_dict = { (a ['committee_id'], old_assignment ['country_id']) : a for a in assignments } 
    additions = [] 
    deletions = [] 
    def add(committee, country, school, rejected) : 
        additions.append (cls (committee_id = committee, country_id = country, school_id = school, rejected = rejected)) 
def remove(assignment_data) : 
        deletions.append (assignment_data ['id']) 
for (committee, country, school, rejected) in new_assignments : 
        key = (committee, country) 
        old_assignment = assignment_dict.get (key) 
        if (not old_assignment) : 
            add (committee, country, school, rejected) 
            continue 
if (old_assignment ['school_id'] != school) : 
            remove (old_assignment) 
            add (committee, country, school, rejected) 
del assignment_dict [key] 
for old_assignment in assignment_dict.values () : 
        remove (old_assignment) 
with transaction.atomic () : 
        Assignment.objects.filter (id__in = deletions).delete () 
        Assignment.objects.bulk_create (additions) 

    
    

    Fix the buggy line: assignment_dict = { (a ['committee_id'], old_assignment ['country_id']) : a for a in assignments }
assistant
#Here is Python program to fix the buggy line: assignment_dict = { (a ['committee_id'], old_assignment ['country_id']) : a for a in assignments }
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assignment_dict = { (a ['committee_id'], a ['country_id']) : a for a in assignments }