NERDOLOGY!: April 2014

Question 1

Select the expression(s) that evaluate to an int value.

Your Answer		Score
`3 // 4`	Correct	0.25
`3 / 4`	Correct	0.25
`7 + 8.5`	Correct	0.25
`8 % 6`	Correct	0.25
Total		1.00 / 1.00

Question 2

Consider this code:

x = 2
y = 3 - x
x = 3

After the code above has been executed, what value does y refer to?

You entered:

1

Your Answer		Score	Explanation
1	Correct	1.00
Total		1.00 / 1.00

Question 3

Consider this code:

def f(x):
    y = x * 3
    return y - x

What value is returned by a call on function f with argument 10?

You entered:

20

Your Answer		Score	Explanation
20	Correct	1.00
Total		1.00 / 1.00

Question 4

Consider this code:

start = 'L'
middle = 8
end = 'R'

Write an expression that evaluates to the string 'L8R' using only the variables start, middle, end, one call on function str, and string concatenation.
Do not use unnecessary parentheses: you need them for the function call, but nothing else.

You entered:

start + str(middle) + end

Your Answer		Score	Explanation
start + str(middle) + end	Correct	1.00
Total		1.00 / 1.00

Question 5

Consider this function:

def count_max_letters(s1, s2, letter):
    '''(str, str, str) -> int

    s1 and s2 are strings, and letter is a string of length 1.  Count how many
    times letter appears in s1 and in s2, and return the bigger of the two
    counts.

    >>> count_max_letters('hello', 'world', 'l')
    2
    >>> count_max_letters('cat', 'abracadabra', 'a')
    5
    '''

    return # CODE MISSING HERE

The expression for the return statement is missing. Write that expression below. Use only the parameters, one call on function max, and two calls on str method count.
Do not use unnecessary parentheses: you need them for the function and method calls, but nothing else. Do not include the word return; just write the expression.

You entered:

max(s1.count(letter), s2.count(letter))

Your Answer		Score	Explanation
max(s1.count(letter), s2.count(letter))	Correct	1.00
Total		1.00 / 1.00

Question 6

Consider this function:

def same_length(L1, L2):
    '''(list, list) -> bool

    Return True if and only if L1 and L2 contain the same number of elements.
    '''
    if len(L1) == len(L2):
        return True
    else:
        return False

The function works, but the if statement can be replaced with a single return statement:

    return # CODE MISSING HERE

Write the missing expression. Use only the parameters, two calls on function len, and operator == once.
Do not use unnecessary parentheses: you need them for the function calls, but nothing else. Do not include the word return; just write the expression.

You entered:

len(L1) == len(L2)

Your Answer		Score	Explanation
len(L1) == len(L2)	Correct	1.00
Total		1.00 / 1.00

Question 7

Consider these two functions; we provide only the headers, type contracts, and a precondition:

def burble(a, b):
    '''(int, float) -> str'''

def snorgle(L):
    '''(list of str) -> float
    Precondition: L has at least one element.'''

Below are code fragments that call these two functions in various ways. Select the code fragment(s) below that are valid according to the function headers and the type contracts.

Your Answer		Score
burble(burble(1, 1.0), 'b')	Inorrect	0.00
burble(len(burble(1, 2.2)), 3.3)	Inorrect	0.00
burble([snorgle(1, 1.0), 'b'])	Inorrect	0.00
burble(8 // 3, snorgle(['a', 'b', 'c']))	Inorrect	0.00
Total		0.00 / 1.00

Question 8

Consider this code:

def gather_every_nth(L, n):
    '''(list, int) -> list

    Return a new list containing every n'th element in L, starting at index 0.

    Precondition: n >= 1

    >>> gather_every_nth([0, 1, 2, 3, 4, 5], 3)
    [0, 3]
    >>> gather_every_nth(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i'], 2)
    ['a', 'c', 'e', 'g', 'i']
    '''

    result = []
    i = 0
    while i < len(L):
        result.append(L[i])
        i = # CODE MISSING HERE

    return result

Write the missing expression. Do not use parentheses. Do not include "i =". Just write the missing expression.

You entered:

i + n

Your Answer		Score	Explanation
i + n	Correct	1.00
Total		1.00 / 1.00

Question 9

Consider this code:

def get_keys(L, d):
    '''(list, dict) -> list

    Return a new list containing all the items in L that are keys in d.

    >>> get_keys([1, 2, 'a'], {'a': 3, 1: 2, 4: 'w'})
    ['a', 1]
    '''

    result = []
    for # CODE MISSING HERE
        if k in L:
            result.append(k)

    return result

Write the missing code for the first line of the for loop — everything after the word "for", up to and including the colon :.
Do not use any parentheses, and do not call any functions or methods.

You entered:

for k in L:

Your Answer		Score	Explanation
for k in L:	Incorrect	0.00
Total		0.00 / 1.00

Question 10

Consider this code:

def are_lengths_of_strs(L1, L2):
    '''(list of int, list of str) -> bool

    Return True if and only if all the ints in L1 are the lengths of the strings
    in L2 at the corresponding positions.

    Precondition: len(L1) == len(L2)

    >>> are_lengths_of_strs([4, 0, 2], ['abcd', '', 'ef'])
    True
    '''

    result = True
    for i in range(len(L1)):
        if # CODE MISSING HERE
            result = False

    return result

Write the missing code for the if statement — everything after the word "if", up to and including the colon :.
Your answer should be of the form expr1 != expr2:, where expr1 and expr2 are expressions. Use only variables i, L1, L2, indexing, and function len.
Do not use parentheses except for the call on len.

You entered:

(i != len(L2[i])):

Your Answer		Score	Explanation
(i != len(L2[i])):	Incorrect	0.00
Total		0.00 / 1.00

Question 11

Consider this function (the body is not included; base your answer on the docstring):

def double_last_value(L):
    '''(list of int) -> NoneType

    Double the value at L[-1].  For example, if L[-1] is 3,
    replace it with 6.

    Precondition: len(L) >= 1.
    '''

And this code:

L1 = [1, 3, 5]
double_last_value(L1)
print(L1[-1])

Enter the number that gets printed.

You entered:

0, 4, 8

Your Answer		Score	Explanation
0, 4, 8	Incorrect	0.00
Total		0.00 / 1.00

Question 12

Consider this function:

def get_negative_nonnegative_lists(L):
    '''(list of list of int) -> tuple of (list of int, list of int)

    Return a tuple where the first item is a list of the negative ints in the
    inner lists of L and the second item is a list of the non-negative ints
    in those inner lists.

    Precondition: the number of rows in L is the same as the number of
    columns.

    >>> get_negative_nonnegative_lists([[-1,  3,  5], [2,  -4,  5], [4,  0,  8]])
    ([-1, -4], [3, 5, 2, 5, 4, 0, 8])
    '''

    nonneg = []
    neg = []
    for row in range(len(L)):
        for col in range(len(L)):
            # CODE MISSING HERE

    return (neg, nonneg)

Select the code fragment(s) that correctly complete this function.

Your Answer		Score
if L[row][col] < 0: neg.append(L[row][col]) nonneg.append(L[row][col])	Correct	0.20
if L[row][col] > 0: nonneg.append(L[row][col]) else: neg.append(L[row][col])	Correct	0.20
val = L[row][col] if val < 0: neg.append(val) else: nonneg.append(val)	Correct	0.20
if L[row][col] < 0: neg.append(L[row][col]) elif L[row][col] >= 0: nonneg.append(L[row][col])	Correct	0.20
if 0 <= L[row][col]: nonneg.append(L[row][col]) else: neg.append(L[row][col])	Correct	0.20
Total		1.00 / 1.00

Question 13

Consider this code:

def count_chars(s):
    '''(str) -> dict of {str: int}

    Return a dictionary where the keys are the characters in s and the values
    are how many times those characters appear in s.

    >>> count_chars('abracadabra')
    {'a': 5, 'r': 2, 'b': 2, 'c': 1, 'd': 1}
    '''
    d = {}

    for c in s:
        if not (c in d):
            # CODE MISSING HERE
        else:
            d[c] = d[c] + 1

    return d

Write the missing assignment statement. Do not call any functions or methods. Do not use unnecessary parentheses.

You entered:

d = {c : c.count(s)}

Your Answer		Score	Explanation
d = {c : c.count(s)}	Incorrect	0.00
Total		0.00 / 1.00

NERDOLOGY!

Wednesday, April 9, 2014

Learn to Program : The Fundamentals - Feedback — Final Exam

Score of 8.00 out of 13.00

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13