class Sample:
    def __init__(self):
        self.contents = {}
    def insert(self, item):
        self.contents[item] = self.contents.get(item, 0) + 1
    def erase_one(self, item):
        if item in self.contents:
  	      del self.contents[item]
    def erase_many(self, matchCriteria):
          tempDict = self.contents.copy()
          for currentItem in tempDict:
               if currentItem == matchCriteria:
                  self.erase_one(currentItem)
    def list_items(self):
          for currentItem in self.contents:
            print currentItem

test = Sample()
test.insert(1)
test.insert(1)
test.insert(2)
test.erase_many(1)
test.list_items()