What accounts for the following behavior when using "print" in Python

Question

I have the following code:

 import numpy as np
 import math as mat

 list_of_numbers = {int(mat.sqrt(x)) for x in range(7)}

 print(list_of_numbers)

I was expecting the output to be the square root of each number from zero to 6.

i.e., [0, 1, 1, 1, 2, 2, 2]

Why is it that Python only prints

[0, 1, 2]

It seems that there is no reference about print not printing duplicate values. Can anyone help?

Change `{}` to `[]`. `{}` is for set and `[]` is for list. Set will only have unique elements so the output is correct — Sohaib Farooqi, Oct 23 '17 at 03:29

erewok · Accepted Answer · 2017-10-23T03:36:21.670

3

You have created a set literal here:

list_of_numbers = {int(mat.sqrt(x)) for x in range(7)}

Sets don't store duplicates. They're useful data structures for checking membership for things that can be hashed.

They are definitely not the same thing as lists.

To create a list, you just need to swap { and } for [ and ]:

 list_of_numbers = [int(mat.sqrt(x)) for x in range(7)]

edited Oct 23 '17 at 03:36

answered Oct 23 '17 at 03:29

erewok

This answer gives the OP an answer to why his code is not working, but doesn't give an actual solution to help him fix his code. Perhaps you could show him how to create a list? – Trevor Jex Oct 23 '17 at 03:34
fair enough. added. – erewok Oct 23 '17 at 03:36

score 2 · Answer 2 · edited Oct 23 '17 at 03:34

2

It is because you are using a Set instead of a List. Try:

import numpy as np
import math as mat

list_of_numbers = [int(mat.sqrt(x)) for x in range(7)]

print(list_of_numbers)

edited Oct 23 '17 at 03:34

Trevor Jex

answered Oct 23 '17 at 03:30

Yachay J. Tolosa

score 2 · Answer 3 · edited Oct 23 '17 at 03:38

2

You need to change

list_of_numbers = {int(mat.sqrt(x)) for x in range(7)}

to

list_of_numbers = [int(mat.sqrt(x)) for x in range(7)]

edited Oct 23 '17 at 03:38

Pang

answered Oct 23 '17 at 03:34

user6606453

3 Answers3