程序代做CS代考 python interpreter CS 61A Structure and Interpretation of Computer Programs – cscodehelp代写
CS 61A Structure and Interpretation of Computer Programs
Fall 2015
INSTRUCTIONS
Midterm 1
• You have 2 hours to complete the exam.
• The exam is closed book, closed notes, closed computer, closed calculator, except one hand-written 8.5” × 11”
crib sheet of your own creation and the official CS 61A midterm 1 study guide.
• Mark your answers on the exam itself. We will not grade answers written on scratch paper.
Last name
First name
Student ID number
BearFacts email
TA
Name of the person to your left
Name of the person to your right
All the work on this exam is my own.
(please sign)
2
1. (12 points) Evaluators Gonna Evaluate
For each of the expressions in the table below, write the output displayed by the interactive Python interpreter when the expression is evaluated. The output may have multiple lines. If an error occurs, write “Error”.
Hint: No answer requires more than 5 lines. (It’s possible that all of them require even fewer.)
The first two rows have been provided as examples.
Recall: The interactive interpreter displays the value of a successfully evaluated expression, unless it is None. Assume that you have started python3 and executed the following statements:
def jazz(hands):
if hands < out:
return hands * 5 else:
return jazz(hands // 2) + 1
def twist(shout, it, out=7): while shout:
shout , out return lambda out:
hands, out = 2, 3
Expression
pow(2, 3)
= it(shout), print(shout , out)
print(shout ,
out)
Interactive Output
8
print(4, 5) + 1
45 Error
print(None, print(None))
jazz(5)
(lambda out: jazz(8))(9)
twist(2, lambda x: x-2)(4)
twist(5, print)(out)
twist(6, lambda hands: hands-out, 2)(-1)
Name: 3 2. (12 points) Environmental Policy
(a) (6 pt) Fill in the environment diagram that results from executing the code below until the entire program is finished, an error occurs, or all frames are filled. You may not need to use all of the spaces or frames.
A complete answer will:
• Add all missing names and parent annotations to all local frames. • Add all missing values created or referenced during execution.
• Show the return value for each local frame.
1 2 3 4 5 6 7 8 9
10 11 12 13
func the(donald) [parent=Global]
func clin(ton) [parent=Global]
def the(donald):
return donald + 5
def clin(ton):
def the(race):
return donald + 6
def ton(ga):
donald = ga-1
return the(4)-3
return ton
donald, duck = 2, clin(the)
duck = duck(8)
Global frame
the clin
f1: ___________ [parent=____________]
Return Value
f2: ___________ [parent=____________]
Return Value
f3: ___________ [parent=____________]
Return Value
4
(b) (6 pt) Fill in the environment diagram that results from executing the code below until the entire program is finished, an error occurs, or all frames are filled. You may not need to use all of the spaces or frames. The
A complete answer will:
• Add all missing names and parent annotations to all local frames. • Add all missing values created or referenced during execution.
• Add all missing parents of function values.
• Show the return value for each local frame.
Global frame
inside
fear
disgust
f1: inside [parent=Global]
Return Value
f2: ___________ [parent=____________]
Return Value
f3: ___________ [parent=____________]
Return Value
1 2 3 4 5 6 7 8
func inside(out) [parent=Global]
func λ(fear)
func λ(disgust)
func λ(fear)
def inside(out):
anger = lambda fear: fear(disgust)
fear = lambda disgust: anger(out)
disgust = 3
fear(5)
fear, disgust = 2, 4
inside(lambda fear: fear + disgust)
f4: ___________ [parent=____________]
Return Value
Name: 5 3. (10 points) Digit Fidget
**IMPORTANT DEFINITION** Each digit in a non-negative integer n has a digit position. Digit posi- tions begin at 0 and count from the right-most digit of n. For example, in 568789, the digit 9 is at position 0 and digit 7 is at position 2. The digit 8 appears at both positions 1 and 3.
(a) (3 pt) Implement the find_digit function, which takes a non-negative integer n and a digit d greater than 0 and less than 10. It returns the largest (left-most) position in n at which digit d appears. If d does not appear in n, then find_digit returns False. You may not use recursive calls.
def find_digit(n, d):
“””Return the largest digit position in n for which d is the digit.
>>> find_digit(567, 7) 0
>>> find_digit(567, 5) 2
>>> find_digit(567, 9) False
>>> find_digit (568789 , 3
8) # 8
appears at
positions
1 and 3
“””
i, k = 0, ______________________________________________________________
while n:
n, last = n // 10, n % 10
if last == _________________________________________________________:
________________________________________________________________
i=i+1
return _________________________________________________________________
(b) (2 pt) Circle all values of y for which the final expression below evaluates to True. Assume that find_digit is implemented correctly. The compose1 function appears on the left column of page 2 of your study guide.
123456789
f = lambda x: find_digit (234567 , x) compose1(f, f)(y) == y
6
(c) (3 pt) Implement luhn_sum. The Luhn sum of a non-negative integer n adds the sum of each digit in an even position to the sum of doubling each digit in an odd position. If doubling an odd digit results in a two-digit number, those two digits are summed to form a single digit. You may not use recursive calls or call find_digit in your solution.
def luhn_sum(n):
“”” Return the Luhn
>>> luhn_sum(135) 12
>>> luhn_sum(185) 13
sum of n.
# 1 + 6 + 5
# 1 + (1+6) + 5
>>> luhn_sum(138743) # From lecture: 2 + 3 + (1+6) + 7 + 8 + 3 30
“””
def luhn_digit(digit):
x = digit * ________________________________________________________
return (x // 10) + _________________________________________________
total , multiplier = 0, 1
while n:
n, last = n // 10, n % 10
total = total + luhn_digit(last)
multiplier = __________________________________________ – multiplier
return total
(d) (2 pt) A non-negative integer has a valid Luhn sum if its Luhn sum is a multiple of 10. Implement check_digit, which appends one additional digit to the end of its argument so that the result has a valid Luhn sum. Assume that luhn_sum is implemented correctly.
def check_digit(n):
“””Add a digit to the end of n so that the result has a valid Luhn sum.
>>> check_digit(153) # 2 + 5 + 6 + 7 = 20 1537
>>> check_digit (13874)
138743
“””
return _________________________________________________________________
Name: 7 4. (6 points) Zombies!
**IMPORTANT** In this question, assume that all of f, g, and h are functions that take one non-negative integer argument and return a non-negative integer. You do not need to consider negative or fractional numbers.
(a) (4 pt) Implement the higher-order function decompose1, which takes two functions f and h as arguments. It returns a function g that relates f to h in the following way: For any non-negative integer x, h(x) equals f(g(x)). Assume that decompose1 will be called only on arguments for which such a function g exists. Furthermore, assume that there is no recursion depth limit in Python.
def decompose1(f, h):
“””Return g such that h(x) equals f(g(x)) for any non-negative integer x.
>>> add_one = lambda x: x + 1
>>> square_then_add_one = lambda x: x * x + 1
>>> g = decompose1(add_one , square_then_add_one)
>>> g(5) 25
>>> g(10) 100
“””
def g(x):
def r(y):
if ____________________________________________________________:
return ____________________________________________________
else:
return ____________________________________________________
return r(0)
_______________________________________________________________________
(b) (2 pt) Write a number in the blank so that the final expression below evaluates to 2015. Assume decompose1 is implemented correctly. The make_adder and compose1 functions appear on the left column of page 2 of your study guide.
e, square = make_adder(1), lambda x: x*x
decompose1(e, compose1(square , e))(3) + ______________________________________
