Search code examples
pythongenerator

Why does an integer inside a generator function swallow the object of send()?

I am not trying to achieve anything -- apart from learning how generator functions and coroutines work on a brick level, which I am not really getting yet, despite lots of reading....

$cat test.py 

#No integer
def eee():
    num = yield
    print(f"First num: {num}")
    num = yield
    print(f"Second num: {num}")
    num = yield
    print(f"Third  num: {num}")

#integer
def ddd():
    yield 100
    num = yield
    print(f"First num: {num}")
    num = yield
    print(f"Second num: {num}")
    num = yield
    print(f"Third  num: {num}")

e=eee()
e.send(None)
e.send(1)
e.send(2)
try:
    e.send(3)
except StopIteration as e: 
    print(f'Done with e: {e}\n')

d=ddd()
print(d.send(None))
d.send(1)
d.send(2)
d.send(3)

$python3   test.py 
First num: 1
Second num: 2
Third  num: 3
Done with e: 

100
First num: 2
Second num: 3

why does d swallow the num 1?

Solution

  • d "swallows" the 1 you sent it because you added this line

    yield 100

    to ddd, that wasn't in eee.

    That line receives the 1. The 2 goes to the next yield.