Step 2 - Multiple Coroutines

Lets take a look at a call flow calling multiple coroutines concurrently.

def generator():
    # do something
    yield # something
    # do something else
    yield # something else
    # do another thing
    return # some value

def other_generator():
    # do something
    yield # something
    # do something else
    return # other value


gen1 = generator()
next(gen1)
gen2 = other_generator()
next(gen1)
next(gen2)
try:
    next(gen1)
except StopIteration as e:
    some_value = e.value
try:
    next(gen2)
except StopIteration as e:
    other_value = e.value

sequenceDiagram participant c as Caller participant g1 as Generator participant g2 as Other Generator activate c activate c c->>g1: send/next deactivate c activate g1 activate g1 g1-->>c: yield deactivate g1 activate c c->>g2: send/next deactivate c activate g2 activate g2 g2-->>c: yield deactivate g2 activate c c->>g1: send/next deactivate c activate g1 g1-->>c: yield deactivate g1 activate c c->>g1: send/next deactivate c activate g1 g1->>c: return/StopIteration deactivate g1 deactivate g1 activate c c->>g2: send/next deactivate c activate g2 g2->>c: return/StopIteration deactivate g2 deactivate g2 deactivate c

Summary

• The caller can use several coroutines concurrently.

• The caller is in control which coroutine and when a coroutine is resumed.

• The caller needs to catch the StopIteration exception of each coroutine to get the return values.