Why the output of this code is like this?

Question

import numpy
arr = numpy.arange(3,15,3)
print(arr[2])

Answer is 9 however I am not sure why?
Another thing my interpreter is PyCharm is calling out - No module named numpy?

Answer 1

1. numpy.arange will make a new array with numbers from 3 to 15 with 3 steps(like using for loop to append the loop number to the array but taken 3 by 3)

ex. arr=numpy.arange(3,15,3)
=> [3,6,9,12]

"""

similar to:

for i in range(3,15,3)
arr.append(i)

"""

print(arr[0])
output: 3

print(arr[2])
output: 9

more info: https://www.geeksforgeeks.org/numpy-arange-JUMP_LINK__&&__python__&&__JUMP_LINK/

edit: thanks to Russ, forgot it doesn't count the last element(15 in this case).

2. I don't understand well the second question, but if it shows you no module named numpy(and if that's the problem), it's because you need to install the library.

windows: open cmd -> (write) pip install numpy

edit: I haven't worked with PyCharm before so I only know to tell you the windows install option one...

Answer 2

numpy.arange(3, 15, 3) will produce the following list :
[3, 6, 9, 12]
Thus, arr[2] is 9.
This function behave like the range function : start, end, step.

If your python interpreter is saying 'module X not found', you have to install it using pip. Or it must be possible directly in Pycharm, I don't really know. Look on forums, you'll find an answer.