Difference between null and none in Python
Introduction
First, keep in mind that null is not part of the Python programming language syntax, though you can find it in other programming languages (ex. Java, JavaScript). In Python syntax, it is None. So what is None ? Do we really need it ? how is it used ?
let us discuss that…
None in plain English
None has no special meaning other than what the Python syntax has given it. It is a convenient way to indicate that a particular variable has no object value assigned. For example, you may declare a variable and assign it the None value before you instantiate a given class. Another example is to call a function that does not return any value. In this case, None is returned by default. Take a look…
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# A function that returns nothing def func(x): print(x) y = func('TEST') # This is going to print: None print(y) |
That is what None means in plain English but what does it mean technically?
Technical meaning of None
Technically speaking, None is an instance of the NoneType object type (class if you like). It is a singleton (there is only one instance during the lifetime of the program). It is read only, you can not modify the attributes of that object otherwise you get syntax errors. Take a look…
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# Assign None to x x = None # This is going to print: <class 'NoneType'> print(type(x)) |
As we indicated earlier, None is used to refer to the lack of value so during the course of program execution, it is a common task to check if a given variable is None. How can we do that ? Take a look at the following code snippets…
Comparison code snippets
In Python, there are various ways to perform comaprison. We can test for equality or check the identity of objects. The following code snippet demonstrates equality and identity checks….
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class Rectangle: # Initialize width and height def __init__(self, w, h): self.w = w self.h = h # Assume equality is based on area def __eq__(self, rect): return self.area() == rect.area() # Calculate area def area(self): return self.h * self.w # Define two rectangles with same area rect1 = Rectangle(3, 2) rect2 = Rectangle(2, 3) # They are equal becasue they have # the same area print(rect1 == rect2) # But they are not the same because # they are not the same object print(rect1 is rect2) class Weird: # This weird object is equal # to any other object def __eq__(self, other): return True # Define weird objects weird1 = Weird() weird2 = None # This is true because the weird # object returns true no matter # what the other object is even if None print(weird1 == weird2) # Weird and None are two different objects # so this is going to be false print(weird1 is weird2) |
Can we use boolean logic to test for None ? Yes we can ! None behaves in a similar way to empty collections, when casted to a boolean, it returns a False. Here is an example…
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x = None if (x): print("YES") else: print("NO") if (not x): print("TRUE”) |
The output should be something like…
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NO TRUE |
Finally, which method is best to check for None ? I leave that up to the reader but I personally think it is recommended to use identity check using the (is) operator because None in Python is a special purpose object that can be uniquely identified.
Summary
- None in Python is a convenient way to indicate that a particular variable has no object value assigned
- Technically speaking, None is the sole instance of the NoneType object type
- To test for None, we can use equality, identify or boolean checks
That is it for today. Thanks for visiting. Please comment below if you have questions.
About Author
Mohammed Abualrob
Software Engineer @ Cisco