CSE 231 Lab 7

Topics to cover Mutable List vs Immutable Tuples Shallow and deep copy operations LISTS and tuples in functions A Python list is a sequence of objects. It is a sequence like a string. It shares characteristics such as indexing & slicing, iteration (for) and membership (in) as well as functions such as len().

Mutable List vs Immutable Tuples List can be changed or modified whereas tuple can’t be changed or modified Using a tuple instead of a list can give the programmer and the interpreter a hint that the data should not be changed. List has more functionality than the tuple.

Shallow and deep copy operations Shallow copy constructs a new object and then inserts references into it to the objects found in the original. In [3]: colours2[1] = "green“ In [4]: print(colours1) In [1]: colours1 = ["red", "blue"] In [2]: colours2 = colours1 ['red', 'green']

Shallow and deep copy operations Deep copy constructs a new object and then, recursively, inserts copies into it of the objects found in the original. In [1]: import copy In [2]: lst1 = ['a','b',['ab','ba']] In [3]: lst2 = copy.deepcopy(lst1) In [4]: lst2[2][1] = "d" In [5]: lst2[0] = "c“

Do these in PythonTutor.com L1 = ['a','b','c'] L2 = [1,L1,2] print(L2) L1[1] = 'X' [1, ['a', 'b', 'c'], 2] [1, ['a', 'X', 'c'], 2] What is the output?

Do these in PythonTutor.com L3 = L2 L4 = L2[:] L1.append(100) print(L3) print(L4) What is the output? [1, ['a', 'X', 'c', 100], 2]

Do these in PythonTutor.com print(L3 is L2) print(L4 is L2) L2.append('axe') print(L3) print(L4) True False What is the output? [1, ['a', 'X', 'c', 100], 2, 'axe'] [1, ['a', 'X', 'c', 100], 2]

Do these in PythonTutor.com import copy L5 = copy.deepcopy(L2) print(L5) print(L2) What is the output? [1, ['a', 'X', 'c', 100], 2, 'axe']

Do these in PythonTutor.com L2.append(222) print(L5) print(L2) What is the output? [1, ['a', 'X', 'c', 100], 2, 'axe'] [1, ['a', 'X', 'c', 100], 2, 'axe', 222]

LISTS and tuples in functions def doubleStuff(alist): for position in range(len(alist)): alist[position] = 2 * alist[position] things = [2, 5, 9] doubleStuff(things) print(things) lst = [2, 5, 9] doubleStuff(lst[:]) print(lst) [4, 10, 18] [2, 5, 9]

LISTS and tuples in functions def doubleStuff(atuple): for position in range(len(atuple)): atuple[position] = 2 * atuple[position] things = (2, 5, 9) doubleStuff(things) print(things) TypeError: 'tuple' object does not support item assignment Tuple are immutable cannot be modified after creation

LISTS and tuples in functions def newStuff(atuple): atuple=2*atuple things = (2, 5, 9) newStuff(things) print(things) (2, 5, 9)