How to Solve AttributeError: 'list' Object Attribute 'append' Is Read-Only

We can run different operations (methods) on the data type when working with lists in Python. We must understand how they work to use them effectively and without errors.

To uses these methods, we need to know their syntax, errors, and mode of operation. One of these many methods is the append() method, which helps us add a new element to a list.

However, if we misuse it, we will get an AttributeError: 'list' object attribute 'append' is read-only error message.

This article will show you what causes this AttributeError: 'list' object attribute 'append' is read-only error message and how to solve it.

Use the Correct Syntax to Solve AttributeError: 'list' object attribute 'append' is read-only

The AttributeError: 'list' object attribute 'append' is read-only error message is an AttributeError which means that an attribute reference or assignment fails.

We can understand what might be happening from the error message. The object attribute append is read-only, and a referencing or assignment operation is failing because of this condition.

When data is read-only, which append is, it can only be accessed but not modified. Therefore, in our code, there is an expression trying to modify the 'list' object attribute 'append'.

Let us try to replicate the same error message using a simple Python code.

In this code, we create a variable, shopList, which holds a list of elements. Then, another variable, value, binds to a string, toothpick.

Afterward, it prints the content of shopList. And finally, it tried to append the binding value to the list shopList.

Code:

shopList = ["banana", "orange", "sugar", "salt"]
value = "toothpick"
print(shopList)
shopList.append = value

Output:

['banana', 'orange', 'sugar', 'salt']
Traceback (most recent call last):
  File "c:\Users\akinl\Documents\Python\alt.py", line 4, in <module>
    shopList.append = value
AttributeError: 'list' object attribute 'append' is read-only

We can see the error message AttributeError: 'list' object attribute 'append' is read-only we intend to solve. From the error, we know the cause of the error is present in line 4.

The code below is what’s present in line 4:

shopList.append = value

Now, what’s wrong here?

The attribute is called append. The code tried to assign the binding value to the append method, which resulted in errors and exceptions because you shouldn’t replace methods on built-in objects.

What caused the AttributeError is a SyntaxError concerning how to use the append method. The correct way to use the append method can be seen below:

shopList.append(value)

Now, let’s rewrite the same code.

shopList = ["banana", "orange", "sugar", "salt"]
value = "toothpick"
print(shopList)
shopList.append(value)
print(shopList)

Output:

['banana', 'orange', 'sugar', 'salt']
['banana', 'orange', 'sugar', 'salt', 'toothpick']

Therefore, check your syntax when faced with an AttributeError because the same error can be seen with other methods such as index.

Code:

shopList = ["banana", "orange", "sugar", "salt"]
shopList.index = "banana"

Output:

Traceback (most recent call last):
  File "c:\Users\akinl\Documents\Python\index.py", line 2, in <module>
    shopList.index = "banana"
AttributeError: 'list' object attribute 'index' is read-only

This time the error is AttributeError: 'list' object attribute 'index' is read-only instead of an append one.

Always be careful with your syntax.