[Python] 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?

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