Python Programming

Now that we hopefully really understand OOP, let us take a look at some methods provided by different built-in Python collections.

List methods

• lst.sort() - sorts the list in-place (does not return it – it returns None). This is called a mutator method. Use the function sorted() if you want a copy returned instead.
• lst.reverse() - reverses the list in-place (again does not return it). Use the function reversed() if you want a copy returned.
• lst.insert(index, value) - inserts value at the given index shifting elements to the right
• lst.append(value) - adds the value to the end of the list (does not return it)
• lst.index(value) - returns the index of the first instance of value
• lst.remove(value) - removes the first instance of value
• lst.extend(lst2) - adds the elements of lst2 to the end of lst
• lst.count(value) - counts the number of instances of value in the list
• lst.pop(index) - removes and returns the element at the given index (removes and returns the last item if index is not given
• lst.clear() - empties the list

Set methods

• These are equivalent to the set operators discussed in earlier modules
  • s1.union(s2)
  • s1.intersection(s2)
  • s1.difference(s2)
  • s1.symmetric_difference(s2)
  • s1.issubset(s2)
  • s1.issuperset(s2)
• s1.isdisjoint(s2) - returns if there are no common elements
• s.add() - adds a single element to the set
• s.update() - adds multiple elements to the set
• s.intersection_update() - modifies a set by intersection
• s.difference_update() - modifies a set by difference
• s1.symmetric_dfference_update(s2) - modifies a set by symmetric difference
• s.discard(elem) - removes elem if elem is in the set
• s.remove(elem) - removes elem if elem is in the set, otherwise it raises an error
• s.pop() - removes and returns an arbitrary element
• s.clear() - removes all elements from the set s