Is there any way to make a "for" loop in python double my index value after each iteration?

Question

In C++, I can easily write a for loop like below that achieves this purpose

for(int i = 1; i < 100; i *= 2){}

Is there any way to make a for loop in Python do the same thing? Or is the while loop the only way I can do this.

Answer 1

for loops don't do any incrementing; they iterate over an iterable instead.

You can create a generator function that produces your number sequence as an iterable:

def powers_of_two(start, stop=None):
    if stop is None:
        start, stop = 1, start  # start at 1, as 0 * 2 is still 0
    i = start
    while i < stop:
        yield i
        i *= 2

for i in powers_of_two(129):
    # ...

Demo:

>>> for i in powers_of_two(129):
...     print(i)
...
1
2
4
8
16
32
64
128

Answer 2

A generator can be written that, somewhat similar to the C++ for loop, takes an expression in form of a lambda function to manipulate the loop variable.

def func_range(func, start, stop=None):
    start, stop = (0, start) if stop is None else (start, stop)
    while start < stop:
        yield start
        start = func(start)


for i in func_range(lambda x: x*2, 1, 100):
    print(i)

Answer 3

Use the power operator.

In [1]: [2**j for j in range(7)]
Out[1]: [1, 2, 4, 8, 16, 32, 64]