For loop iterate over powers of 2

Question

I want to write a for loop that will iterate over the powers of 2 for each loop.

For example I would want a range like this:

2, 4, 8, 16, ... , 1024
         


        

Answer 1

You'll need to create your own function:

def doubling_range(start, stop):
    while start < stop:
        yield start
        start <<= 1

This uses a left-shift operation; you could also use start *= 2 if you find that clearer.

Demo:

>>> def doubling_range(start, stop):
...     while start < stop:
...         yield start
...         start <<= 1
... 
>>> for i in doubling_range(2, 1025):
...     print i
... 
2
4
8
16
32
64
128
256
512
1024