None in Python refers to a situation where no value has been assigned to a variable. None in Python doesn’t necessarily mean empty.
Python does not use null. Instead, there is a None data type used to represent a variable that is empty but not by zero. When a variable is assigned nothing, it returns None.
None doesn’t associate with boolean data types either. To elaborate, None is not equal to True or False.
In this tutorial, we are going to learn what a list is, the None data type, and how to append None to a list.
What Is a List?
A list is the most primal data type of the Python language. It is used to store different elements under a single name. It is similar to an array in other programming languages with a little difference. While a list can store heterogeneous elements, an array can’t.
The elements of the list are enclosed within square brackets. A list is a mutable data type in Python. A mutable data type can be changed after initialization or declaration. At the same time, an immutable data type cannot be changed.
Related: Read this post to know more about immutable data types.
Let us see an example of a list and a few operations.
lis=['Akarsh','Bindhu','Chandana','Dikshit','Fathima','Farhan']
print("The elements of the list are:\n",lis)
print("The data type of the list is:\n",type(lis))
lis.append('Anand')
print("The updated list is\n",lis)
lis.extend([1,2,3])
print("The extended list elements are:\n",lis)
lis.insert(0,'Akash')
print("The updated list is:\n",lis)
print("The length of the list is:\n",len(lis))
lis.remove('Bindhu')
print("The list after removal is:\n",lis)
print("Sub-list of the original list is:\n",lis[3:])
print("The length of the list after removal is:\n",len(lis))
So in the first line of the code, we are creating a list of elements enclosed in square brackets stored in a variable called lis. The list is printed in the second line.
The data type of the list we just created is checked in the third line with the help of type constructor.
The append function is used to add an element to the end of the list. In the fourth line, we are appending a string called Anand to the list. The new list is printed in the next line.
The extend function is used to add multiple elements to the end of the list. In the sixth line, we extend the list by adding elements 1,2, and 3.
The insert function is used to insert an element at a specified position. In this code, we add the string Akash at the start of the list. Since indexing starts from zero, the string is inserted at the start.
The length of the list is computed with the help of len function. We are computing the list length we created in the tenth line.
The remove function is used to delete a specific element from the list. We are removing the element called Bindhu from the list.
We can even slice the list and print the sublist using the colon(:).
Lastly, we are printing the length of the list after removal.
What Is None Data Type?
The None in Python represents a variable or a data type not assigned a value. We can not associate the None data type with boolean data types either. When a variable is assigned to None, and we check its data type, it returns the class NoneType.
Visit this article to know more about the None type.
Let us see an example.
ls=None
print("The elements of the list are:\n",ls)
print("The type of the variable is:\n",type(ls))
In the first line of code, we assign a None value to a variable called ls. In the next line, we are printing the values in the variable. We are also checking the data type of the variable.
The output is shown below.
Let us check if None equals True or False.
ls = None
print("The type of the variable is:\n",type(ls))
if ls is not None:
if ls == 'True':
print("True")
elif ls == 'False':
print("False")
else:
print("The Variable is None")
With the previous example, we have understood that when a variable is assigned to None, the variable’s data type is returned as None. But let us assume it is not the case just for a second and check if None equals boolean types. That is what we are doing in the above code. We are defining an if statement saying the variable is not None. When executing this code, the control goes into the inner loop and checks if None equals True. If so, True is printed. Else if None is equal to False, False is printed. If the variable is not equal to None, the inner loop is not executed, and the statement after else is printed.
How to Append None to a List?
There are several ways to append None to a list. When using append, the new element is added at the end of the list. If we want to place None elsewhere, append can not be used in Python.
Appending None to a List by Append()
Using the append function to insert None at the end of the list is the most simple way to complete the task. We need to create a list, call the function, and that’s it.
lis=['Akarsh','Bindhu','Chandana','Dikshit','Fathima','Farhan',1,2,3,4]
print("The original list before appending None is:\n",lis)
lis.append(None)
print("The new list is:\n",lis)
We are creating a variable called lis to store a list of elements. This list is printed before appending None to it.
Next, we call the append function to append None to the list.
The new list is printed at the end.
Appending None to a List by Extend()
This is similar to the above example, but the difference remains in the syntax of the extend function.
lis1=[1,2,3,4,'Hello','World']
print("The original list before appending None is:\n",lis1)
lis1.extend([None])
print("The new list is:\n",lis1)
A new list called lis1 is created to store a new list. This list is printed in the next line using the print function.
The extend function is used to insert None at the end of the list. The updated list is printed in the next line.
Appending None by +=
The += operator is used to assign a value to a variable. We will use this assignment operator to add the None value and assign it to the list.
lis2=['Hello','Welcome to','AskPython',8,9]
print("The original list before appending None is:\n",lis2)
lis2+=[None]
print("The new list is:\n",lis2)
We created a new list that is stored in a variable called lis2. This list is printed in the next line.
We used the += operator to add and assign the None value to the list. The updated list is printed in the next line.
Assigning None to a Variable and Appending It to a List
In this example, we will create a variable and assign None. This variable is then appended to the list.
var=None
lis3=['Hello','Welcome to',8,9]
print("The original list before appending None is:\n",lis3)
lis3.append(var)
print("The new list is:\n",lis3)
A variable called var is created and is assigned None. We created a new list and stored it in a new variable called lis3. This list is printed in the next line. The variable which has None is appended to the end of the list.
The updated list is printed in the next line.
Conclusion
To conclude, we have learned about the None data type in Python. It refers to a variable or data type that has no value assigned to it.
The None value does not associate with any boolean and is not equal to zero. The None value has its data type class-NoneType.
We have seen an example of the same.
Next, we learned about a list and understood some crucial operations performed on a list in an example.
Coming to appending None to a list, we have seen four approaches.
In the first method, we used the append function to add the None value at the end of the list.
Coming to the second, we have observed how we can add None to the end of the list using the extend function.
In the third example, we have used the assignment operator to add the None value and assign it later.
Lastly, we have assigned None a variable and appended this variable to the end of the list.
References
Learn more about the None data type from here.
You can find all the list operations in the official Python documentation.
This stack overflow discussion provides more approaches to the same topic.