[SOLVED] Iti 1120 lab # 6 while loops, lists …
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Go to the page below in your interactive textbook
-read through
-click Forward until reaching the end on the Python Visualizing
example (to understand it)
-and answer the two questions and the end:
https://runestone.academy/ns/books/published/py4e-int/iterations/while.html
A solution with forloop
def sum_odd_for(n):
odd_sum = 0
for num in range(n):
if num % 2 == 1:
odd_sum = odd_sum + num
return odd_sum
A solution with a whileloop
def sum_odd_while(n):
odd_sum = 0
i=1
while i < n:
if i % 2 == 1:
odd_sum = odd_sum + i
i=i+1
return odd_sum
Study of while vs for … in some elementary functions:
Problem: sum of positive odd integers smaller than n
list_sum = 0
Problem: Sum of odd
A solution with forloop
numbers in a given list a
A solution with a whileloop
def sum_list_for(a):
”’ (list)->num ”’
list_sum = 0
for i in range(len(a)):
if a[i] % 2 == 1:
list_sum = list_sum
return list_sum
def sum_list_while(a):
”’ (list)->num
i=0
while i < len(a):
if a[i] % 2 == 1:
list_sum = list_sum
+a[i] i=i+1
return list_sum
+ a[i]
6
7
def minimum_for_v2(a):
”’ (list)->num ”’
minimum = a[0]
for i in range(len(a)):
if a[i] < minimum:
minimum = a[i]
return minimum
Study of while vs for … in anotherimportant elementary functions:
Two solutions with forloop
(forloop over elements and overindices)
def minimum_for_v1(a):
”’ (list)->num ”’
minimum = a[0]
for element in a:
if element < minimum:
minimum = element
return minimum
A solution with a whileloop
def minimum_while(a):
”’ (list)->num”’
minimum = a[0]
i=0
while i < len(a):
if a[i] < minimum:
minimum = a[i]
i=i+1
return minimum
Problem:
find a minimum element in a list (of length at least 1)
8
Task 2 and Programming Exercise1
After studying the previous four functions
1.Open the file called seven_functions.py Copy/paste, one by
one, the three solutions labeled with “# with while loop” into
Python visualizer. Run through each example and understand how
the solutions work and how the variables change in the loops.
Play by changing what variable i is initialized to and how it is
incremented (do for example i=i+3) and see what happens. As
always, you can find python visualizer here (make sure you
choose Python 3)
http://www.pythontutor.com/visualize.html#mode=edit
2.Programming exercise 1: Open file called prog-ex-1.py
Complete the function sum_odd_while_v2 that takes an integer n
as input parameter and computes the sum of all odd integers
between 5 and n (inclusively). Use WHILE LOOP only and NO IF
STATEMENTS.
>>> sum_odd_while_v2(10)
21
>>> sum_odd_while_v2(-7)
0
Programming Exercise2
Write a program using while loop that
•asks the user for two integers (one by one
or at the same time if you know how to
handle it). Then it adds them and displays
the sum.
Then the user is asked to enter ‘yes’ if she
wishes to perform the operation again, and
otherwise if she enters anything other than
‘yes’ the program terminates. The operation
(described in the bullet above) is repeated,
as long as the user enters ‘yes’.
Task 3
Question 1. What does the program below print ifthe input user entered was:
1 5 -3 0
Question 2.Can you tell what the program does? Write one sentence
explaining what the functiondoes, in plain English.
Task 4
Question 1. How many times does
the program below print aha?
Task 5
Question 1. What does the
the code on the right
print?
ps. sometimes I say code,
sometimes I say program.
I mean the same thing.
Task 6
13
A programmer who wrote a function below thinks that the
function tests if a given positive integer n>=2 is a prime.
However there is a logical mistake.
1. Where is the mistake?
2. For what number does the function return a wrong answer?
Can you think of the smallest such number?
3. Fix the mistake.
Programming Exercise3
Write a function first_neg that takes a (possibly empty) list of
numbers as input parameter, finds the first occurrence of a
negative number, and returns the index (i.e. the position in the
list) ofthat number.Ifthe list contains no negative numbers orit
is empty, the program should return None. Use while loop (and
not for loop) and your while loop should stop looping once the
first negative number isfound.
Test yourfunction with atleastthe examples below
>>> first_neg([2, 3, -1, 4, -2])
2
>>> first_neg([2, 3, 1, 4, 2])
>>> first_neg([])
Programming Exercise4
Write a function sum_5_consecutive thattakes a list of numbers as input and
returns True ifthere are 5 consecutive numbers in the listthat sum to zero.
Otherwise itreturns False. The function should also return False ifthe list has
less than 5 elements
Solve this in twoways:
1.for loop (over indices of the list)
2.while loop (over indices of thelist)
In both cases you need to think about “stopping condition” in order to avoid
“IndexError: list index out of range
”
3. Test your function with at least the examplesbelow
>>> sum_5_consecutive([2, 3,
True
-3, 2, 4,-6])
>>> sum_5_consecutive ([-10,
False
1, 1, 4, 2, 10, 13])
>>> sum_5_consecutive([2, 1,
True
-3, -3, -3, 2, 7, 4, -6])
>>> sum_5_consecutive ([])
False
>>> sum_5_consecutive ([1, -1,0])
False
Programming Exercise 5 :
Different ways to create usefullists
Recall, for example, that
a=[2] creates a list (refer to by variable a) with one element, a number
2 in this case.
b=[None] creates a list with one element. That element is an object of
type None. That is sometimes useful when we are not ready yet to assign a
value to an element of a list.
c=[] creates an empty list, i.e. a list of length zero
Recall further that multiplying a list by an integer n, creates a new
list that repeats the given list n times. Or that applying ‘+’ operator
to two lists creates a new lists that concatenates the given two lists.
For example:
[1,2]+[10,20,0] creates a list [1,2,10,20,0]
[7,2]*3 creates a list [7,2,7,2,7,2]
Finally, recall the slicing. For example, if a=[2,3,4,1], a[:] returns a
new list that is a copy of list a.
Open the file called creating_various_lists.py. The firstline is given to you.It asks the user to enter a positive
even integer n. For each green programing exercise below, try to find at least two solutions (e.g. one by
using a loop with accumulator pattern and another by using int*list).
1.Create a list a (i.e a listreferred to by variable a) of length n filled with zeros
2.Create a list b of length n filled with random integers between 1 and 100
3.Create a variable c that is an alias of b
4.Setfirst half ofthe elements of c to zero, and then print both b and c
5.Copy list b into a listd
6.Create a new list e that has every 2nd element of b
Programming Exercise 6: FibonacciNumbers
Write a function called fib(n)thattakes as input an integer n (greater
than 1) and creates a list containing n values such that
a[0] =1
a[1] =1
a[i] = a[i-1] + a[i-2]for all i in the range 1 < i < n
and it prints thatlist once it creates it
>>> fib(7)
[1 1 2 3 5 8 13]
Once you are done,trace your program on paper and then Python
visualizerto see whatthe values in the list will be for n=5.
Programming Exercise7:
Write a function inner_productthatthattakes as input two lists of
integers (of same length) and then computes and returns the inner
product ofthe two lists ofintegers.The inner product of
two lists x = [x1, x2,…,xn] and y = [y1, y2,…,yn]is the value
x1 y1 + x2 y2 + …+ xn yn .
>>> inner_product([2,3,4], [1,0,2])
10
Moreprogramming exercises (outside of lab):
Do everything in the first 13 exercises here
https://runestone.academy/ns/books/published/py4e-int/lists/Exercises.html
********
and if you need more exercises….
go to the web site below, for some more practice programming questions but be
aware that the web site is in Python 2,thus if you do these exercises do them on
your own computerAND NOT in the little browser window ofthe web site.
http://codingbat.com/python