Lecture "Brute-force algorithms", exercise 4

[essepuntato]

Write in Python the function def my_range(stop_number) which behave like the built-in function range() introduced in Section "Insertion sort" and returns a proper list, and accompany the function with the related test case. It is not possible to use the built-in function range() in the implementation.

[delfimpandiani]

Ok, so this one I found both easier (because in terms of operations, finding the range was clearer than the enumeration) and harder than the previous exercise.

As I understood, the instruction was to define in Python a function called my_range(input_list) which should behave like the built-in function range(). In the lecture notes Section "Insertion sort", it says that inputting range(4) returns the range([0, 1, 2, 3]), which is a kind of list. However, when I tried it in Python, instead of range([0, 1, 2, 3], it returned range(0, 4) -- meaning, it did not return a "list" per se.

Therefore, I decided to opt for a solution that got me closer to the "list" result as defined in the lecture notes, in the form of range([0, 1, 2, 3]). My solution returns the list, but it does not return it as a function with the word 'range'.

def my_range(input_list):
    result = (list()) # new empty list where to store the resulting list
    len_input_list = len(input_list) #the list length is the same as the range I am trying to find
    for i in range(len_input_list):  # for each number in the range (between 0 and the list length)
        new_item = i #create a new item of the result list, which will be a number
        result.append(new_item) # apend the item to the new list
    return result
    

# accompany the function with the related test case

# Test case for the algorithm
def test_my_range(input_list, expected):
    result = my_range(input_list)
    if expected == result:
        return True
    else:
        return False

# Three different test runs
print(test_my_range([15, 38, 56, 4], [0, 1, 2, 3]))
print(test_my_range(["A", "B"], [0, 1]))
print(test_my_range(["A", 78, "Hola"], [0, 1, 2]))

# True
# True
# True

I'll keep an eye out for you guys' answers, to see how to include range() in the result of the user-defined function. Otherwise, Prof. @essepuntato, could you please clarify if it is necessary, and if so, how to do it? Thank you 👍

[hizclick]

The range() function has two sets of parameters.
start: Starting number of the sequence.
stop: Generate numbers up to, but not including this number. For example, range(0, 4) generates integers from 0 up to, but not including, 4.

so the function my_range has 3 inputs one for starting number, the second one for ending number and the last one to accept an input list.
range(3, 6)= 3,4,5
range(0,9) = 0,1,2,3,4,5,6,7,8
in a list=[1,2,3,4,5,6,7] range(1,5), will out put [2,3,4,5]
for the list ["ab","cd","eg","hi","jk"] and range(1,4) the out put will be ["cd","eg","hi"]

here is my code I think it will work for all inputs

def get_range(end,items="",start=0): #initializing the start position to 0
	my_list=[]
	if len(items)!= 0: #check if a list is passed to get_range() function
		for position, item in enumerate(items):
			if(start<=position<end):
				my_list.append(item)
		return my_list
	else:
		end = end -1
		while start<=end:
			my_list.append(end)
			end -=1
		my_list.reverse()
		return my_list

def test_get_range(expected,end,items="",start=0):
	result = get_range(end,items,start)
	if result == expected:
		return True
	else:
		return False
		 
print(test_get_range([2,3],3,[1,2,3,4],1)) 
#expected result, ending number, items in the list, starting position
print(test_get_range([1,2,3],4,"",1))
print(test_get_range([3,4,5],6,"",3))
print(test_get_range([2,3],3,[1,2,3,4,5],1))
print(test_get_range([2,3,4,5],5,[1,2,3,4,5,6,7],1))
print(test_get_range(["cd","eg","hi"],4,["ab","cd","eg","hi","jk"],1))
print(test_get_range(["cd","eg","hi","jk"],4,["ab","cd","eg","hi","jk"],1))

#true
#true
#true
#true
#true
#true
#false

[essepuntato]

Hi @delfimpandiani

It is not possible to use the built-in function range() in the body of your my_range function. However there is a clear mistake in the definition of the exercise (my fault), since range takes in input a number –– apologises!

[hizclick]

def test_my_range(n,expected):
	if my_range(n) == expected:
		return True
	else:
		return False
def my_range(n):
	n= n- 1
	my_list=[]
	while n>=0:
		my_list.append(n)
		n -= 1
	my_list.reverse()
	return(my_list)
print(test_my_range(4,[0,1,2,3]))
print(test_my_range(3,[0,1,2]))
print(test_my_range(5,[0,1,2,3,4]))
print(test_my_range(6,[0,1,2,3]))

#True 
#True 
#True  
#False

[federicabologna]

My method is basically identical to the one implemented by @Hizkie . In fact, the only difference is that I subtract "1" inside the while loop, instead of before the while statement.
Still, I had problems in printing the function, since Python would return "<list_reverseiterator object at 0x000001AAB7D662B0>".

def my_range(n):
    result = []
    while n > 0:
        n -= 1
        result.append(n)
    return reversed(result)

print(my_range(4))

<list_reverseiterator object at 0x000001AAB7D662B0>

Then, I looked up my colleagues' answers and found that they expressed the inversion as "result.reverse()" and not as "reversed() - the second option was the one presented in class. After using that expression, Python finally returned the expected results.

def test_my_range(n, expected):
    result = my_range(n)
    if result == expected:
        return True
    else:
        return False

def my_range(n):
    result = []
    while n > 0:
        n -= 1
        result.append(n)
    result.reverse()
    return(result)

print(test_my_range(4, [0, 1, 2, 3]))
print(test_my_range(3, [3, 2, 1]))

True
False

@essepuntato Professor, my questions are now:
1 - what does the code returned by Python mean?
2 - what is the difference between the two expressions?

[delfimpandiani]

Given Prof. Peroni's edit of the prompt, I looked at Hizkiel's solution and decided to find a similar solution but without having to reverse the list. I used his same test examples and it works just as well:

def test_my_range(n,expected):
    if my_range(n) == expected:
        return True
    else:
        return False
def my_range(stop):
    n= 0
    my_list=[]
    while n<=(stop -1):
        my_list.append(n)
        n += 1
    return(my_list)
print(test_my_range(4,[0,1,2,3]))
print(test_my_range(3,[0,1,2]))
print(test_my_range(5,[0,1,2,3,4]))
print(test_my_range(6,[0,1,2,3]))

#True 
#True 
#True  
#False

[delfimpandiani]

Given Prof. Peroni's edit of the prompt, I looked at Hizkiel's solution and decided to find a similar solution but without having to reverse the list. I used his same test examples and it works just as well:

def test_my_range(n,expected):
    if my_range(n) == expected:
        return True
    else:
        return False
def my_range(stop):
    n= 0
    my_list=[]
    while n<=(stop -1):
        my_list.append(n)
        n += 1
    return(my_list)
print(test_my_range(4,[0,1,2,3]))
print(test_my_range(3,[0,1,2]))
print(test_my_range(5,[0,1,2,3,4]))
print(test_my_range(6,[0,1,2,3]))

#True 
#True 
#True  
#False

[MattiaSpadoni]

I tried like this, sorry, but screenshots are the easiest way to share it (yes I have 1158 unread e-mails).

[EleonoraPeruch]

# Test case for the algorithm
def test_my_range(stop_number, expected):
    result = my_range(stop_number)
    if expected == result:
        return True
    else:
        return False

# Code of the algorithm
def my_range(stop_number):
    stop_number >= 0    # my_range takes a non negative number as input
    # return a list of values from 0 
    # to the one preceding stop_number
    output_my_range = list() # the list to return
    input_number = 0         # the list starts from 0 
    while input_number < stop_number: 
            output_my_range.append(input_number)
            input_number += 1
    return output_my_range

# Run some tests
print(test_my_range((4), ([0, 1, 2, 3])))
print(test_my_range((4), ([0, 1, 2, 3, 4])))
print(test_my_range((4), ([0, 1, 2])))

True
False
False

[SeverinJB]

# Testing Algorithm
def test_my_range(input_value, expected): 
    result = my_range(input_value) 
    if expected == result: 
        return True 
    else: 
        return False

# Algorithm
def my_range(input_value): 
    range_object = []
    while input_value > 0: 
        input_value = input_value - 1
        range_object.append(input_value)
    range_object.reverse()
    return range_object

# Testing Input
print(test_my_range(3, [0,1,2]))
print(test_my_range(4, [0,1,2,3]))
print(test_my_range(0, []))

[friendlynihilist]

@essepuntato: Professor, while reaching the same conclusions (more or less), I've also experienced the exact same problem mentioned by my colleague @federicafaithbologna. Could reversed(<input_list>) be used in this code instead of result.reverse(). Thank you!

def test_my_range(stop_number, expected):
    result = my_range(stop_number)
    if expected == result:
        return True
    else:
        return False

def my_range(stop_number):
    result = []

    while stop_number > 0:
            stop_number = stop_number - 1
            result.append(stop_number)
    result.reverse() #question about this
    return result


print(test_my_range(6, [0, 1, 2, 3, 4, 5])) #true
print(test_my_range(7, [0, 1, 2, 3, 4, 5, 6, 7])) #false
print(test_my_range(5, [0, 1, 2, 3])) #false
print(test_my_range(4, [0, 1, 2, 3])) #true

[ilsamoano]

#test
def test_myrange(n,expected):
    result= myrange(n)
    
    if result == expected:
        return True
    else:
        return False
        
#code
def myrange(n):
    newlist = []
   
    while n >0:
        n = n - 1
        newlist.append(n)
    newlist.reverse()
    return newlist

#test evaluation
print (test_myrange(4,[0,1,2,3,]))

[mangiafrangette]

def test_my_range(stop_number, expected):
    return my_range(stop_number) == expected

def my_range(stop_number):

    stop_number = stop_number - 1
    range_list = []
    while stop_number >= 0:
        range_list.append(stop_number)
        stop_number = stop_number -1

    return list(reversed(range_list))

stop_number = 9
expected = list(range(stop_number))
print(test_my_range(stop_number, expected))

[tceron]

Thanks to the help of @delfimpandiani I was finally able to run it. :D