Dynamic Lists

1. Dynamic Lists CSIS 1595: Fundamentals of Programming and Problem Solving 1

2. Dynamic Lists • List sizes in Python can change dynamically • Append new elements to end • Insert new elements into list • Remove elements from list • Implemented as methods on list variables • Not true of all data types (arrays in C, etc.) • Common data structure in programming

3. Dynamic List Methods • list.append(element) • Adds elementto end of list • Increases size of list by 1

4. Dynamic List Methods • list.insert(i, element) • Inserts elementbefore the element at index iof list • Increases size of listby 1 • Inserting at 0 puts new element at beginning of list • Can’t insert at end – must use append instead

5. Dynamic List Methods • list.remove(element) • Removes the first instance of element fromlist • Decreases size of listby 1 • Error if no such element in list

6. Creating New Lists • Use [] to create new empty list • Can then append elements as needed • Shortcut: list = [value for index in range(0, size)]

7. Other Useful Methods • len(list) number of elements in list • Useful for iteratingthrough dynamic list • May not know how many elements are currently in list!

8. Other Useful Methods • list.count(element) • Returns number of timeselement found in list • 0 if elementnotin list • Useful for avoiding errors when removing elements • Check whether count > 0 first

9. Example: Sorted Lists • Goal: • User repeatedly enters numbers to store in list • Keep list sorted from lowest to highest • Idea: • Find where new number should be placed and insertthere • Algorithm: • If list empty (length == 0) then append to end • If new number greater than any so far, append to end • New number > number at index length – 1 • Else loop from start of list until find element > new number • Insert new number at that point

10. Example: Sorted Lists