Nonetype object has no attribute append ошибка

The Python

append()

is a list method to add a new element object at the end of the list. But if we use a

append()

method on a NoneType object, we encounter the

AttributeError: 'NoneType' object has no attribute 'append'

.

In this Python tutorial, we will explore this error and learn why it occurs and how to solve it. To understand the error better, we will discuss a typical scenario where most Python learners encounter this error.

So, let’s get started!

NoneType is a type for the None object, which has no value. Functions that don’t return anything has the return value ‘None’. When we use the append() method on the NoneType object, we receive the error

AttributeError: 'NoneType' object has no attribute 'append'

.

The error has two parts —

1. Exception Type (
   
AttributeError

   )
2. Error Message (
   
'NoneType' object has no attribute 'append'

   )

1. Exception Type (

AttributeError

)

AttributeError is one of the standard Python exceptions. It occurs when we try to access an unsupported attribute (property or method) using an object.

For example, the

append()

method is exclusive to Python lists. But if we try to apply it to a tuple object, we receive the AttributeError. This is because tuple objects do not have the

append()

method.

tuple_ = (1,2,3,4,5)
tuple_.append(6)  #error

Output

Traceback (most recent call last):
  File "/home/main.py", line 2, in <module>
    tuple_.append(6)  #error
AttributeError: 'tuple' object has no attribute 'append'

2. Error Message (

'NoneType' object has no attribute 'append'

)

The error message

'NoneType' object has no attribute 'append'

» tells us that the

append()

method is not supported on the

NoneType object

. This means we called the

append()

method on a variable whose value is

None

.

Example

# A None value object
a = None

# calling append() method on the None value
a.append(2)

print(a)

Output

Traceback (most recent call last):
File "main.py", line 5, in <module>
a.append(2)
AttributeError: 'NoneType' object has no attribute 'append'

Break the code

In the above example, we received the error at line 5 with the

a.append(2)

statement. The value of

a

is

None

, and None value does not have any

append()

method. Hence, we receive this error.

Causes of AttributeError: ‘NoneType’ object has no attribute ‘append’

There are many reasons for this error to occur:

• Having a function that does not return anything or returns
  
None

  explicitly.
• Setting a variable to
  
None

  explicitly.
• Assigning a variable to the result of calling a function that does not return anything.
• Having a function that returns a value only if the condition is met.

Common Example Scenario

The most common scenario when novice Python programmers commit this error is when they assign the return value of the

append()

method to a Python list variable name and try to call the

append()

method again on the same object. The append() method can only append a new value at the end of the list object, and it does not return any value, which means it returns

None

.

For Example

# list object
my_list = [1,2,3,4,5]

# return value of append method 
return_value = my_list.append(6)

print(return_value)

Output

None

From the output, you can see that we get

None

value when we try to assign the return value of

append()

method to a variable.

Many new Python learners do not know about the

None

return value of the

append()

method. They assign the append() method calling statement to the list object, which makes the list object value to

None

. And when they again try to append a new value to the list, they encounter the

AttributeError: 'NoneType' object has no attribute 'append'

Error.

For Example

Let’s write a Python program for to-do tasks. The program will ask the user to enter the 5 tasks that he/she wants to perform. We will store all those tasks using a list object,

todos

. To add the tasks entered by the user, we will use the list

append()

method.

# create a empty list
todos = []

for i in range(1,6):
    task = input(f"Todo {i}: ")

    # add the task to the todo list
    todos =  todos.append(task)

print("****Your's Today Tasks******")
for i in todos:
    print(i)

Output

Todo 1: workout
Todo 2: clean the house
Traceback (most recent call last):
File "main.py", line 8, in <module>
todos = todos.append(task)
AttributeError: 'NoneType' object has no attribute 'append'

Break the code

In the above example, we get the error at line 8 with the statement

todos = todos.append(task)

. The error occurs during the second iteration of the for loop when we pass the

Todo 2: clean the house

value as an input.

In the first iteration, when we pass the

Todo 1: workout

value, the

todos = todos.append(task)

statement set the value of

todos

to

None

, because the value returned by the

todos.append(task)

statement is None.

That’s why, in the second iteration, when Python tries to call the

append()

method on the

None

object, it threw the

AttributeError: 'NoneType' object has no attribute 'append'

error.

Solution

The solution to the above problem is straightforward. We do not need to assign the return value to any object when we use the append() method on a Python list. The simple call of the append() method on a list object will add the new element to the end of the list.

To solve the above example, we only need to ensure that we are not assigning the

append()

method return value our

todos

list.

Example Solution

# create a empty list
todos = []

for i in range(1,6):
    task = input(f"Todo {i}: ")

    # add the task to the todo list
    todos.append(task)

print("****Your's Today Tasks******")
for i in todos:
    print(i)

Output

Todo 1: workout
Todo 2: clean the house
Todo 3: have a shower
Todo 4: make the breakfast
Todo 5: start coding
****Your's Today Tasks******
workout
clean the house
have a shower
make the breakfast
start coding

Final Thoughts!

This was all about the most common Python error

AttributeError: 'NoneType' object has no attribute 'append'

. The error occurs when we try to call the append() method on a

None

value. To resolve this error, we need to ensure that we do not assign any

None

or return value of the

append()

method to a list object.

If you still get this error in your Python program, you can share your code in the Comment section. We will try to help you with debugging.

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