>>> def f():
...     1
...
>>> f()
>>> b = f()
>>> type(b)
<class 'NoneType'>
>>> def f2():
...     1+2+3
...     b = 6
...
>>> f2()
>>> b = f2()
>>> type(b)
<class 'NoneType'>
>>> type(None)
<class 'NoneType'>