Generator object

Learn the generator object and next() call.

The generator object

When you call a generator function, it returns a generator object; the function body does not run yet. The next() call advances the body up to the first yield.

Example: g = count_up() returns a generator object. next(g) returns 1 and the function pauses at the first yield. The second next(g) returns 2. When all values are exhausted, a StopIteration error is raised.

StopIteration

When a generator has produced all values, the next() call raises StopIteration. The for loop catches this error and ends the loop silently.

You may see this error in manual next() calls. Example: in the generator g = (x for x in [1]), next(g) returns 1, the second next(g) raises StopIteration. So a for loop is usually safer; manual calls need try/except.

Exercise Get values with next

Define the function def gen():; in the body write yield 1 and yield 2. Create a generator object with g = gen(). Print two values with print(next(g)) and print(next(g)).

Show example solution

# gen generator and get values with next
def gen():
    yield 1
    yield 2

g = gen()
print(next(g))
print(next(g))

Test yourself

next call

g = count_up()
print(____(g))

Show answer

g = count_up()
print(next(g))

What does next() do on an exhausted generator?
- Returns None
- Loops forever
- Restarts
- Raises StopIteration
Show answer

Raises StopIteration — On an exhausted generator next() raises StopIteration.
Match the generator object parts

g = gen()

Generator object
next(g)

Next value
StopIteration

Exhaustion error
for v in g

Auto iteration

Next lesson: yield from

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies