So I have the following generator function:
def gen(n=5):
for i in range(n):
n = yield n
for i in gen(3):
print(i)
3
None
None
I understand the first result of yield is 3. Because I assigned 3 to function argument n. But where are the None in the second and third yield coming from? Is it because in the for-loop, yield n returns None and this None is assigned to n in this line: n = yield n?
This is explained in the documentation of yield expressions, especially this part:
The value of the yield expression after resuming depends on the method which resumed the execution. If next() is used (typically via either a for or the next() builtin) then the result is None. Otherwise, if send() is used, then the result will be the value passed in to that method.
As you use a for loop, n just gets None as a value when resuming after the first yield. So, from now on, n is None, and this is what will be yielded the last two times.
send() is designed to change the result value of the yield expression. I thought send() was to insert a new value in the sequence being yielded.It seems to me that you answered your own question:
because in the for-loop, yield n returns None and None is assigned to n in this line: n = yield n
You can read more at this answer.
yieldstatement documentation?