Using Generators and their expressions

[BeerLover]

I am trying to get my head around generators. I do not really understand the concept of generators and their expressions, however I read what they are used for and it seems that I might need them going further when learning Python (3.6). 

There is this code. And the printing just won't work: 

(Python 3.6 (spyder3)) 

def simple_generator_function():
    yield 1
    yield 2
    yield 3
    
our_generator = simple_generator_function()
for i in list(our_generator):
    print((i))

Output:
Error: 
  File "...\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 102, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)
... 
print((i))

UnsupportedOperation: not writable

Why can not I print this iterable object?  (print(list(i)) doesn't work either)