Question

I have the following code in Python:

for i in range(4):
  if self.start == self.corners[i]:
    self.visitedCorners += (1 << i)

I’m working with co-ordinates. self.start and self.corners are co-ordinates.

So with the code on the top I want to check whether the start is a corner.
If the start is the same of a corner, I do that shift. But, how does that shift work?

I don’t want any other code; I just want to understand this code.

Answer 1

All that 1 << i does is produce the number with the i-th least significant bit set to 1 and all other bits set to 0:

>>> for i in range(4): print bin(1 << i)
... 
0b1
0b10
0b100
0b1000

In the code, self.visitedCorners is a bit mask, where the four least significant bits correspond to the four corners. Each iteration of the for i loop sets the corresponding bit in self.visitedCorners to 1 (provided the if condition holds).