# CSI31_Lecture25_set.py

from copy import copy

class Set:

  def __init__(self,elements):
    
    self._elements = []

    for item in elements: # iterate over the sequence elements
      if item not in self._elements: # exclude duplicates
        self._elements.append(item)

  def addElement(self,x):

    if x not in self._elements:
      self._elements.append(x)

  def deleteElement(self,x):
    
    try:
      self._elements.remove(x)
    except:
      print(x, "is not in the set")

  def member(self,x):

    return x in self._elements

  def intersection(self,set2):

    newList = []

    # choose the set with smaller number of elements
    if len(self._elements) < len(set2._elements):
      for item in self._elements: # iterate over the elements of this set
        if set2.memeber(item): # if item is also an element of set2
          newList.append(item)
    else: # iterate over the elements of set2
      for item in set2._elements:
        if item in self._elements: # if item is also an element of this set
          newList.append(item)

    return Set(newList)


  def union(self,set2):

    newList = copy(self._elements) # copy all elements of set to new list

    for item in set2._elements: # iterate over the elements of the second set
      if item not in newList:
        newList.append(item)

    return Set(newList)

  def subtract(set2):

    newList = []

    for item in self._elements: # iterate over the elements of this set
      if not set2.member(item): # check if the element is not in the set2
        newList.append(item)

    return Set(newList)