Run 'main' and Run selection yields different results.

I am trying to run a simple python program in PyCharm,

import sys

# for i in open("test"):
for i in sys.stdin or []:
    data = i.split()
    a = int(data[0])
    b = int(data[1])
    print(abs(a-b))

When I press shift+F10 the code runs and prompts me for input. All is good.

But when I select the code and press Alt + Shit + E (Run selection) I get the following error in Python Console,

Traceback (most recent call last):
File "<input>", line 4, in <module>
TypeError: 'StdIn' object is not iterable

Why the discrepancy?

Thank you!