Python: IDLE won’t display anything for an expression evaluated to None

This is trivial but sometimes misleading.

>>> 1
1
>>> 2
2
>>> 'Foo'
'Foo'
>>> None  # Nothing displayed on the next line
>>> b = None
>>> b  # Nothing displayed on the next line

Most misleading when a generator yields a None–it does yield something, just not displayed:

>>> def gen_none():
...     yield None
... 
>>> g = gen_none()
>>> next(g)  
>>> # Did it yield a value?

However,

>>> str(None)
'None'
>>> repr(None)
'None'
>>> print(None)
None

Jupyter notebooks behave the same way. See Stack Overflow: Display None values in IPython。