Question

I have a generator that will keep giving numbers that follow a specific formula. For sake of argument let’s say this is the function:

# this is not the actual generator, just an example
def Generate():
    i = 0
    while 1:
        yield i
        i+=1       

I then want to get a list of numbers from that generator that are below a certain threshold. I’m trying to figure out a pythonic way of doing this. I don’t want to edit the function definition. I realize you could just use a while loop with your cutoff as the condition, but I’m wondering if there is a better way. I gave this a try, but soon realized why it wouldn’t work.

l = [x for x in Generate() x<10000] # will go on infinitely

So is there a correct way of doing this.

Thanks

Answer 1

An itertools solution to create another iterator:

from itertools import takewhile
l = takewhile(lambda x: x < 10000, generate())

Wrap it in list() if you are sure you want a list:

l = list(takewhile(lambda x: x < 10000, generate()))

Or if you want a list and like inventing wheels:

l = []
for x in generate():
    if x < 10000:
        l.append(x)
    else:
        break