I want to learn how to use the return value of a generator (but this not what I'm concerned with now).
After searching, they said that I can get the return value from StopIteration when the generator is exhausted, so I tested it with the following code:
def my_generator():
yield 1
yield 2
yield 3
return "done"
def exhaust_generator(_gen):
print("===============================================\n")
print("exhaust_generator")
try:
while True:
print(next(_gen))
except StopIteration as e:
print(f"Return value: '{e.value}'")
def exhaust_generator_iter(_gen):
print("===============================================\n")
print("exhaust_generator_iter")
try:
for i in _gen:
print(i)
print(next(_gen))
except StopIteration as e:
print(f"Return value: {e.value}")
gen = my_generator()
gen2 = my_generator()
exhaust_generator(gen)
exhaust_generator_iter(gen2)
===============================================
exhaust_generator
1
2
3
Return value: 'done'
===============================================
exhaust_generator_iter
1
2
3
Return value: None
As you can see, the return value is different between the two versions of exhausting the generator and I wonder why.
Searched google but it has not been helpful.
In your first example with the while, you're catching the first StopIteration exception raised by the generator when it's initially exhausted.
In your second example with the for, you're catching a subsequent StopIteration exception raised by calling next() a second time after the generator has already been exhausted (by the for, which caught that initial exception).