Python 2 - "For counting loop"

Question

I am working on a project for school in python 2 and I am having a lot of trouble with one of the problems:

Write a program that computes the following sum: sum = 1.0/1 + 1.0/2 + 1.0/3 + 1.0/4 + 1.0/5 + .... + 1.0/N N is an integer limit that the user enters.

For example:
Enter N: 4
Sum is: 2.08333333333

The code I currently have written is:

NumOfN = int(input("What is N? : "))
total = 0
for i in range (NumOfN):
  NextNum = 1.0/(NumOfN)
  total = NextNum
  NumOfN = NumOfN-1
print "the sum is", total

However whenever I run this I get an output of "1.0" any help would be greatly appreciated.

-Thank you.

This can be done in one line with a list comprehension and sum. total = sum([1.0/x for x in range(1,NumOfN+1)]) — erip
– erip, Commented Jan 7, 2016 at 3:04

icedwater · Accepted Answer · 2016-01-07 04:14:44Z

1

You were not incrementing total with itself and NextNum. I changed total = NextNum to total += NextNum:

NumOfN = int(input("What is N? : "))
total = 0
for i in range(NumOfN):
  NextNum = 1.0/(NumOfN)
  total += NextNum
  NumOfN = NumOfN-1
print "the sum is ", total

or more simply:

NumOfN = int(input("What is N? : "))
runningTab = []
for i in range(NumOfN, -1, -1):
    if i != 0:
        runningTab.append(1.0/(i))

print "the sum is ", sum(runningTab)

It is better to use lists and sum at the end than to keep a running tally of numbers.

edited Jan 7, 2016 at 4:14

icedwater

4,8943 gold badges39 silver badges54 bronze badges

answered Jan 7, 2016 at 3:01

heinst

8,8048 gold badges47 silver badges80 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

heinst Over a year ago

@erip well it does reduce the number of variables used and improves upon a few things. Less code is simplified

Registered User · Accepted Answer · 2016-01-07 03:33:45Z

0

Second line of the for loop:

total = NextNum

The variable total should have NextNum added to it, not just reassigned. This is because total must be added over and over by adding NextNum to itself. Let's change that to:

total = total + NextNum

This would mean: total needs to add NextNum to itself, so we will add them together so that the new total is now equal to the old total + NextNum.

A side note:

You may have noticed that @heinst used += in his line of code, total += NextNum. This is the same as total = total + NextNum , but it is like an abbreviation. You can do this with += , -= , *=,and /=. All of them are ways to abbreviate the line of code that would reassign a variable after doing some arithmetic on it.

With that being said, the following line of code:

NumOfN = NumOfN-1

Can become:

NumOfN -= 1

This is an abbreviation.

answered Jan 7, 2016 at 3:33

Registered User

4843 gold badges8 silver badges32 bronze badges

2 Comments

TheRIProgrammer Over a year ago

I never knew I could do NumOfN -= 1 like that, that will make life a lot easier, thanks

Registered User Over a year ago

No problem :D @TheRIProgrammer

Collectives™ on Stack Overflow

Python 2 - "For counting loop"

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related