Return prime numbers from range

[krzyfigh]

Hi Guys,

Let me begin by confesing I am new to coding.
I understand my problem might seem basic to some but I am also sure you're eager to help one learn.

Here we go. I came up with a problem, I wanted to write a program that will return all prime numbers from a range set by user. I end up not being able to write it and found below code online. It works fine but it also puzzles me why. Especially this line - if (number % i) == 0:

This will break if a number in range "i" is divisible by any number in range "number".
This makes sense to me except for the fact that eventually number will be divided by itself which would also exclude all prime numbers. I wanted to write a line that would run modulo between "I" and "number" excluding I from number, but it doesn't seem necessary.

Help, can you please unconfused me? Why does it work?


print ("all primer numbers in a selected range")

a = int(input("enter bottom value of the range: "))
b = int(input("enter top value of the range: "))

for number in range(a, b +1):
if number > 1:
for i in range(2, number):
if (number % i) == 0:
break
else:
print(number)

[bowlofred]

Make sure you use the python tags for your code, so that it properly shows indentation.

I think your confusion is on the range() function. Lets look at the docs for it (which you can do by typing help(range) at an interactive prompt.

>>> help(range)
Help on class range in module builtins:

class range(object)
 |  range(stop) -> range object
 |  range(start, stop[, step]) -> range object
 |
 |  Return an object that produces a sequence of integers from start (inclusive)
 |  to stop (exclusive) by step.  range(i, j) produces i, i+1, i+2, ..., j-1.
 |  start defaults to 0, and stop is omitted! ...

So the important thing is that the stop element of the range is not returned. (This turns out to be very handy for properly treating ranges that line up with each other). But in your case since number is given as the stop for the range, it will not be returned. So the number % i expression will never be evaluated with i == number.

[krzyfigh]

Thank you