Generator object
- Python course
- Intermediate
- Lesson 101/116
- 5 min
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.
Practice 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)).
Starter code
# gen generator and get values with nextSample solution
# gen generator and get values with next
def gen():
yield 1
yield 2
g = gen()
print(next(g))
print(next(g))Expected output
1 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 next call
g = count_up()
print(____(g))g = count_up()
print(next(g))Explanation: next(g) produces the next value.
2 What does next() do on an exhausted generator?
- Returns None
- Loops forever
- Restarts
- Raises StopIteration Correct answer
Explanation: On an exhausted generator next() raises StopIteration.
3 Match the generator object parts
| Term | Meaning |
|---|---|
g = gen() |
Generator object |
next(g) |
Next value |
StopIteration |
Exhaustion error |
for v in g |
Auto iteration |