What is the difference between calling function with parentheses and without in python?

Question

I have a question. Lets assume that we have function hello(). What is the difference between calling it with parentheses and without? When I call hello() it is referring to

Answer 1

hello refers to the function object, hello() calls the function itself.

For example:

>>> def hello():
...     print "hello"
... 
>>> hello

>>> hello()
hello