Python None is a special constant, which represents a null or absent value. In this tutorial, we will introduce some basic knowledge about on using it.
None is unequal False, 0 or empty list, dictionary, tuple or string.
None means a value is absent, nobody knows its specific value. However, if a variable is 0, False, empty list, dictionary, tuple or string, the value of them are specific.
Here is an example to illustrate the difference among them.
>>> None == 0 False >>> None ==  False >>> None == False False >>> x = None >>> y = None >>> x == y True
Functions that do not return anything will return None
Create a function that does not return any variables
def getValue(x) x = 3
From this function, getValue() return nothing.
y = getValue(5)
y is None.
if None is False and if not None always True
This truth is very helpful, especially you don’t know how to determine what value a variable will be.
>>> content = None >>> if not content: ... print("content is empty.")
Then the output is:
content is empty.