Class is not defined despite being imported
Use the fully-qualified name:
sayinghi = testmodule.Greeter("hello world!")
There is an alternative form of import that would bring Greeter into your namespace:
from testmodule import Greeter
import testmodule
# change to
from testmodule import Greeter
or
import testmodule
sayinghi = Greeter("hello world!")
# change to
import testmodule
sayinghi = testmodule.Greeter("hello world!")
You imported the module/package, but you need to reference the class inside it.
You could also do this instead
from testmodule import *
but then beware of namespace pollution