Python: Printing Third Letter of Sentence

Question

def main (): 
    sentence=input("Please enter a sentence:")
    print("Original Sentence:",sentence)
    sentencelenght=len(sentence)
    for i in range(0, sentencelenght, 3): 
        print("Every third letter:", i)
main()

I am at this point and my output is a bunch of numbers, please explain how I can fix this.

Note we have learned for, while loops, if/or statements more basic stuff. Nothing too complicated.

bash-4.1$ python hw4_part2.py Please enter a sentence:Thanks for the help Original Sentence: Thanks for the help Every third letter: T Every third letter: n Every third letter: Every third letter: r Every third letter: h Every third letter: h Every third letter: p bash-4.1$ — Mehul Gandhi, Feb 29 '16 at 23:15
The output you obtained is the characters in the sentence at positions {0, 3, 6, 9, ...}, which is what the program does. If you update your question with an example input and expected output, people may be able to understand what you want better. — user1952500, Feb 29 '16 at 23:18
This is correct but I want my answer to print, Every third letter: Im....etc — Mehul Gandhi, Feb 29 '16 at 23:20
What do you mean ? Where is 'm' in the sentence 'Thanks for the help' ? — user1952500, Feb 29 '16 at 23:23
If you meant you want only the letters, use `print sentence[i]` — user1952500, Feb 29 '16 at 23:25
To reiterate: please give an example input and output. I and the people answering below are not able to understand the requirements. — user1952500, Feb 29 '16 at 23:31
My answer is coming out as third letter= i, third letter= m and such — Mehul Gandhi, Mar 01 '16 at 00:38
The use `print(sentence[i], end="")`. More details at: http://stackoverflow.com/questions/3249524/print-in-one-line-dynamically — user1952500, Mar 01 '16 at 00:55

zondo · Answer 1 · 2016-02-29T23:00:46.290

4

It's because you are using i, not the character at that position. Change that line to this:

print("Every third letter:", sentence[i])

That is not the most efficient way to print every third letter, however. You don't need the loop; just use print(sentence[::3]). That works because a slice is [start:stop:step]. We are leaving start empty, so it defaults to the beginning. We are leaving stop empty, so it defaults to the end. step, we are defining as 3, so it goes from the beginning to the end using every third letter.

edited Feb 29 '16 at 23:00

answered Feb 29 '16 at 22:55

zondo

19,901
8
44
83

Only problem with this way is that I do not think we are allowed to use that method – Mehul Gandhi Feb 29 '16 at 23:22

pp_ · Answer 2 · 2016-02-29T22:59:28.223

2

You can use slices to print every third letter (starting from the first letter):

print(sentence[::3])

edited Feb 29 '16 at 22:59

answered Feb 29 '16 at 22:56

pp_

3,435
4
19
27

Padraic Cunningham · Answer 3 · 2016-03-01T00:13:07.480

I presume you cannot use slicing and need to use your own code, if you want to print every third character starting from the third, start the range an 2 and keep your step of 3 printing each sentence[i] though the loop:

def main ():
    sentence = input("Please enter a sentence:")
    print("Original Sentence:",sentence)
    # start at the third character
    for i in range(2,  len(sentence), 3):
        # access the string by index 
        print("Every third letter:", sentence[i])

Output:

In [2]: main()
Please enter a sentence:001002003
Original Sentence: 001002003
Every third letter: 1
Every third letter: 2
Every third letter: 3

Python: Printing Third Letter of Sentence

3 Answers3