Referring to The Null Object in Python

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Problem Statement: How to refer to the Null object in Python?

None in Python [A Quick Overview]

In programming languages like C or Java, generally, there is a null pointer available that can be used for different purposes. But the null pointer is not available in Python. Generally, in Java, null is a variable that is empty (to mark default parameters) or a pointer that does not point to anything. However, in Python, null is not characterized by 0 or empty.

text = ""
if text == Null:
    print("No text found")

# Output: NameError: name 'Null' is not defined

The bottom line is that ‘there is no Null keyword available in Python. However, we can use the ‘None‘ keyword that is an object to refer to Null objects.
⦿ Python utilizes “None” to define the null objects and variables.
⦿ None is an instance of the NoneType class.
⦿ None is built-in in Python and is accessible in all modules and classes.
⦿ In Python 2.4 versions or more, it isn’t possible to overwrite None. 
⦿ None can be assigned to any variable, but we cannot create any other NoneType objects. The variables assigned None points to the same object. 
⦿ Ensure that the first letter in the “None” keyword is capital N; otherwise, it may result in an error.

Example:

text = None
if text == None:
    print("Null type detected! Object type : ", type(text))

Output:

Null type detected! Object type :  <class 'NoneType'>

How to Check if Something is of the Type None?

The simplest way to check if something has been assigned “None” as a value is to use the “is” identity operator. The “is” operator tests whether the two variables refer to the same object. It will return True if the value assigned is None and return False if it’s None

Example:

# Checking if the object is None using "is" operator
# Non-empty object
x = 2
print(x is None)
# Null object
y = None
print(y is None)
# An empty function
class Empty(object):
    def __eq__(self, z):
        return not z
        
e = Empty()
print(e is None)

Output:

False
True
False

Caution: Another way to test whether the object is None or not is to use the comparison operators (==, != ). However, using the comparison operator is not advisable as it may also return empty objects and functions as None objects which is logically not the case. Let’s have a look at an example that demonstrates this issue.

Example:

# Checking if the object is None using "==" operator
# Non-empty object
x = 2
print(x == None)
# Null object
y = None
print(y == None)


# This is an empty function not a null function
class Empty(object):
    def __eq__(self, z):
        return not z


def foo():
    pass


e = Empty()
# Note the difference
print(e == None)
print(e is None)

Output:

False
True
True
False

Explanation: In the above example, the “e” object must not return True as it is an empty function and not a None object. However, the comparison operator evaluates it to be True even though it is not a None type object. Hence, it is advisable to use the “is” operator while working with the “None”

Using “None” in List

Let’s create a list with a “None” value in Python. We have to check if the list accepts the None value and whether this value is considered while calculating the length of the list. 

Example:

# Example of a List with None values
l = ['Referring', 'to', None, 'object', 'in', 'Python']
# Length of ist including None values
print("The length of the list is: ", len(l))
# Printing the list values that includes "None"
for i in range(0, len(l)):
    print("The", i + 1, "item on the list is:", l[i])

Output: The output clearly suggests that None is also counted as an element when used in the list.

The length of the list is:  6
The 1 item on the list is: Referring
The 2 item on the list is: to
The 3 item on the list is: None
The 4 item in the list is: object
The 5 item on the list is: in
The 6 item on the list is: Python

Note:None” cannot be associated with any other list method. If we declare a list as None, we cannot use any methods associated with the list. This is true for every other iterable object/data type.

Example:

# Simple list
l1 = [5, 10, 15, 20, 25]
print(l1)
l1.append(30)
print(l1)
# None assigned to list
l2 = None
print(l2)
l2.append(30)
print(l2)

Output:

[5, 10, 15, 20, 25]
[5, 10, 15, 20, 25, 30]
None
Traceback (most recent call last):
  File "<main.py>", line 10, in <module>
AttributeError: 'NoneType' object has no attribute 'append'

In the above example, we can add or delete elements from list1 as list data type allows such methods in Python. However, when we try to append the element to l1 which is assigned to None we get an error. This happens because the 'NoneType' object has no attribute 'append'.

Related Article: [FIXED] AttributeError: ‘NoneType’ object has no attribute ‘something’

Using None as default argument in Python

Example:

# Default value
value = 2


class Number:
    def check(self, x=None):
        # Check if default argument is None
        if x is None:
            x = value
        return x


n = Number()
print("The number is", n.check())
print("The number is", n.check(10))

Output:

The number is 2
The number is 10

Explanation: In the above code, the check method has a default argument x that has been assigned None as the default value. When nothing is passed to check() then x is assigned with the number stored in the variable value as can be seen in the first function call. In the second function call x gets a value of 10 which overrides its default value and the returned value is 10.

Using Pandas to Check if the Object is None

We can also use the Panda’s module in Python to check if the object is referring to None value. You can use the isnull() function of the Pandas module that is used to indicate whether the values are missing from the object (Referenced to None.)

Example:

# Importing pandas module
import pandas as pd
# None object
x = pd.isnull(None)
print(x)
# Non-empty object
z = pd.isnull('Python')
print(z)
# An empty function
class Empty(object):
    def __eq__(self, z):
        return not z
        
e = pd.isnull(Empty())
print(e == None)

Output:

True
False
False

Conclusion

That’s all about today’s discussion. Here’s what we learned today –

  • What is None in Python and how it is referenced.
  • None in a List
  • Using None as a default value
  • Pandas and None

I hope this article has helped you. Please stay tuned and subscribe for more such articles.


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