Description
Assignment
This assignment should be completed in a single Python source (.py) file.
(1) List your answers to the “Comprehension Check: Slices” slide from the second lecture (slide
#12). As a reminder, here are the questions, where s = “PYTHON”:
(a) Write two equivalent expressions to retrieve the character “N” from s.
(b) What is the value of the expression s[0:6]?
(c) What is the value of the expression s[:3]?
(d) What is the value of the expression s[::2]?
(e) Write a slice of s that is equal to “PYTH”.
(f) Write a slice of s that is equal to “HN”.
(g) Write a slice of s that is equal to “NHY”.
(2) Write a function called fiblist(n) that, given a positive integer n, produces a list containing the first n terms of the Fibonacci Sequence. You may assume that n is a positive
integer.
(3) Write a function called ispartitionable(s) that, given a list of integers, return True
if the list can be partitioned into two contiguous slices such that the sum of the elements of
one slice is equal to the sum of the elements of the other slice, False otherwise. You may
assume the list s contains only integers. Formally, the function should return True if the
following holds, and False otherwise:
Di :
i
ÿ´1
j“0
srjs “
len
ÿ
psq´1
k“i
srks
Hint: the built-in function sum(s) is probably useful here.
1
(4) The list comprehension given on slide #15 of the second lecture to generate the n-row
identity matrix uses a nested list comprehension. Write an alternate comprehension that is
not nested to produce the same result, and store that list in a variable called m. Hint: the
sequence repetition (*) and concatenation (+) operators will come in handy.
(5) Write a list comprehension that produces a list containing the sums of the rows in a matrix
m, and store that list in a variable named sums. You may assume m is previously defined.
(6) Write a function called vowelcount(s) that, given a string, returns the number of characters in the string that are English vowels (i.e., one of the characters ‘a’, ‘e’, ‘i’, ‘o’, or
‘u’). The function should be case-agnostic meaning that, e.g., the character ‘A’ counts as a
vowel.
(7) Write a function called listfromcsv(s) that, given a string containing several lines of comma-separated values (e.g., s may be
“5,8,hello,2\n9,14,world,1344”), produces a (2-dimensional) list of those
values separated by line (e.g., for the example given, the result should be the list
[[’5’, ’8’, ’hello’, ’2’], [’9’, ’14’, ’world’, ’1344’]]). Hint: the
string functions str.split(sep) and str.splitlines() will probably come in
handy. This function can be written in one line with a list comprehension.
Challenge Activities
Some homeworks (such as this one) will have additional challenge activities. These activities do
not contribute to your grade, but they are problems that I find interesting or challenging.
(1) Write a function called partition(s) that, given a “partitionable” list of integers, returns
a tuple consisting of two subsequences of s that have identical sums. You may assume the
function ispartitionable(s) returns True. Hint: using the enumerate(s) function
keeps track of both the index and item of s.
(2) Write a function called triangles(n) that, given a positive integer n, produces a list of
the first n triangle numbers. You may assume that n is a positive integer.
2
(3) Write a function called ctriangles(n) that produces a list identical to triangles(n),
but does so using a single-line list comprehension. Hint: the built-in function sum(s) is
probably useful here.
(4) Think about the relative efficiency of triangles(n) and ctriangles(n). How do they
compare? Which is faster? Why?
(5) Write a function called pascal(r) that, given a positive integer r, produces a list containing the first r rows of Pascal’s Triangle (more precisely, the function should only generate
all non-zero entries in the triangle). You may assume that r is a positive integer.
Recall: The kth entry in the nth row of Pascal’s Triangle has the value `
n
k
˘
“
n!
k!pn´kq!
. It
has the nice property that `
n
k
˘
“
`
n´1
k´1
˘
`
`
n´1
k
˘
.
(6) If you used any modules to write pascal(r), write a function called pascal2(r) to
generate the first r rows of Pascal’s Triangle without using any additional modules. Alternatively, if your previous solution did not use any additional modules, write a function
called pascal2(r) that takes advantage of the math module (useful functions may include
math.factorial(n) to compute n! or math.comb(n, k) to compute `
n
k
˘
) to generate
the first r rows of Pascal’s Triangle.1
(7) Write a function called csvfromlist(s) that takes as input a 2-dimensional list and
generates a string with values across rows seprated by ’,’ and rows separated by ’\n’. In
essence, csvfromlist(s) should “undo” the work that listfromcsv(s) did.
Submission
To submit this assignment, upload your .py file containing all of your code to the “Homework
2” assignment on Carmen. As always, be sure to note all group members who contributed to the
assignment and what those contributions were.
1Obviously, pascal2(r) should not simply make a call to pascal(r). The two functions should use different
algorithms altogether.
3
