1. CSE 231 Lab 7

2. 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().

3. 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.

4. 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']

5. 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“

6. 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?

7. 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]

8. 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]

9. 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']

10. 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]

11. 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]

12. 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

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