Is there a difference between running a Python 3 generator with the following (gen) and gen.send (None)?
When you create a Python 3 generator and start running it right away. You will receive an error:
TypeError: can't send non-None value to a just-started generator
And in order to go (send messages or receive something from it) you first have to call __next__
on it: next(gen)
or pass None to it gen.send(None)
.
def echo_back():
while True:
r = yield
print(r)
# gen is a <generator object echo_back at 0x103cc9240>
gen = echo_back()
# send anything that is not None and you get error below
# this is expected though
gen.send(1)
# TypeError: can't send non-None value to a just-started generator
# Either of the lines below will "put the generator in an active state"
# Don't need to use both
next(gen)
gen.send(None)
gen.send('Hello Stack Overflow')
# Prints: Hello Stack Overflow)
Both methods give the same result (start the generator).
What is the difference, if any, between starting the generator with next(gen)
as opposed to gen.send(None)
?
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From generator.send()
:
When send () is called to start a generator, it must be called with None as an argument, because there is no yield expression that could receive a value.
A call next()
on the generator starts execution until the first expression yield
to which no values can be sent None
, which will become the value of that expression yield
(for example, x = yield
>).
Both next(gen)
both gen.send(None)
behave the same (i.e. no difference in usage).
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