Can generator be used more than once?

Question

This is my piece of code with two generators defined:

one_line_gen = (x for x in range(3))

def three_line_gen():
    yield 0
    yield 1
    yield 2


        

Answer 1

three_line_gen is not a generator, it's a function. What it returns when you call it is a generator, a brand new one each time you call it. Each time you put parenthesis like this:

three_line_gen()

It is a brand new generator to be iterated on. If however you were to first do

mygen = three_line_gen()

and iterate over mygen twice, the second time will fail as you expect.

Answer 2

Yes, generator can be used only once. but you have two generator object.

# Python 3


def three_line_gen():
    yield 0
    yield 1
    yield 2

iterator = three_line_gen()
print(iterator)
for x in iterator:
    print(id(iterator), x)

iterator2 = three_line_gen()
print(iterator2)
for x in iterator2:
    print(id(iterator2), x)

And the result is:

<generator object three_line_gen at 0x1020401b0>
4328784304 0
4328784304 1
4328784304 2
<generator object three_line_gen at 0x1020401f8>
4328784376 0
4328784376 1
4328784376 2

Answer 3

no, you can not iterate over a generator twice. a generator is exhausted once you have iterated over it. you may make a copy of a generator with tee though:

from itertools import tee

one_line_gen = (x for x in range(3))
gen1, gen2 = tee(one_line_gen)
# or: 
# gen1, gen2 = tee(x for x in range(3))

for item in gen1:
    print(item)

for item in gen2:
    print(item)

for the other issues see Ofer Sadan's answer.