Readings: Lecture Notes 2.1-2.5
ex2.pyQ1. Draw environment diargram for the following:
def sum_elems(elem):
if type(elem) == int:
return elem
else:
return (sum_elems(elem[0]) + sum_elems(elem[1]))
pairs = ((1, 2), (3, 4))
total = sum_elems(pairs)
Q2. Return the sum of the first n terms of a sequence.
def summation(n, term):
"""Return the sum of the first n terms of a sequence.
>>> summation(5, lambda x: pow(x, 3))
225
"""
Q3. Return a function that applies f twice.
def double(f):
"""Return a function that applies f twice.
f -- a function that takes one argument
>>> double(square)(2)
16
"""
"*** YOUR CODE HERE ***"
Q4. Count the number of occurrences of value in sequence s using a for-loop.
def count(s, value):
"""Count the number of occurrences of value in sequence s using a for-loop.
>>> digits = 1, 8, 2, 8
>>> count(digits, 8)
2
"""
Q5. Recall the definition of the rlist abstract data type.
empty_rlist = None
def rlist(first, rest):
"""Construct a recursive list from its first element and the rest."""
return (first, rest)
def first(s):
"""Return the first element of a recursive list s."""
return s[0]
def rest(s):
"""Return the rest of the elements of a recursive list s."""
return s[1]
Write iterative and recursive functions that reverse a given recursive list, producing a new recursive list with the elements in reverse order. Use only the rlist constructor and first and rest selectors to manipulate recursive lists. (You may use helper functions, but do not duplicate the functionality of len_rlist or getitem_rlist.)
def reverse_rlist_iterative(s):
"""Return a reversed version of a recursive list s.
>>> primes = rlist(2, rlist(3, rlist(5, rlist(7, empty_rlist))))
>>> reverse_rlist_iterative(primes)
(7, (5, (3, (2, None))))
"""
"*** YOUR CODE HERE ***"
def reverse_rlist_recursive(s):
"""Return a reversed version of a recursive list s.
>>> primes = rlist(2, rlist(3, rlist(5, rlist(7, empty_rlist))))
>>> reverse_rlist_recursive(primes)
(7, (5, (3, (2, None))))
"""
"*** YOUR CODE HERE ***"
Q6. Write a function that takes in a sequence and returns the index of the largest element in the sequence:
def index_largest(seq):
"""Return the index of the largest element in the sequence.
>>> index_largest([8, 5, 7, 3 ,1])
0
>>> index_largest((4, 3, 7, 2, 1))
2
"""
assert len(seq) > 0
"*** YOUR CODE HERE ***"
Q7. Create a class called VendingMachine that represents a vending machine for some product. A VendingMachine object doesn't actually return anything but strings describing its interactions. See the doctest below for examples.
class VendingMachine(object):
"""A vending machine that vends some product for some price.
>>> v = VendingMachine('crab', 10)
>>> v.vend()
'Machine is out of stock.'
>>> v.restock(2)
'Current crab stock: 2'
>>> v.vend()
'You must deposit $10 more.'
>>> v.deposit(7)
'Current balance: $7'
>>> v.vend()
'You must deposit $3 more.'
>>> v.deposit(5)
'Current balance: $12'
>>> v.vend()
'Here is your crab and $2 change.'
>>> v.deposit(10)
'Current balance: $10'
>>> v.vend()
'Here is your crab.'
>>> v.deposit(15)
'Machine is out of stock. Here is your $15.'
"""
"*** YOUR CODE HERE ***"