Python: 'list' object attribute 'append' is read-only [Fix]

# Python: 'list' object attribute 'append' is read-only

The Python "AttributeError: 'list' object attribute 'append' is read-only" occurs when you try to set the append attribute on a list object.

To solve the error, call the append() method on the list instead of setting it as an attribute.

Here is an example of how the error occurs.

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a_list = ['bobby', 'hadz', '.']

# ⛔️ AttributeError: 'list' object attribute 'append' is read-only
a_list.append = 'com'

The error occurs because we are trying to set the append attribute on the list object.

Instead, we should call the list.append() method to add an item to the list.

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a_list = ['bobby', 'hadz', '.']

# ✅ Correctly using list.append()
a_list.append('com')

a_list.append('xyz')

# ['bobby', 'hadz', '.', 'com', 'xyz']
print(a_list)

The list.append() method adds the supplied value to the end of the list.

Note that the method returns None as it mutates the original list in place.

If you need to add elements to a list in a loop, click on the following article.

# Modifying the value of a list item at a given index

If you are trying to change the value of a list item at a specific index, use square brackets.

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a_list = ['bobby', 'hadz', '.']

a_list[0] = 'new'

print(a_list) # 👉️ ['new', 'hadz', '.']

You can use the list.index() method if you need to get the index of a value in a list.

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a_list = ['bobby', 'hadz', '.']

print(a_list.index('bobby'))  # 👉️ 0

The method returns the index of the first item whose value is equal to the provided argument.

Notice that we called the method with parentheses () in the same way we called the list.append() method.

If you need to append multiple values to a list, follow the instructions in the next subheading.

# AttributeError: 'list' object attribute 'extend' is read-only

The "AttributeError: 'list' object attribute 'extend' is read-only" error is raised when you try to use the list.extend() method as an attribute.

To solve the error, call the method with parentheses, passing it the values you want to add to the list.

Here is an example of how the error occurs.

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a_list = ['bobby']

# ⛔️ AttributeError: 'list' object attribute 'extend' is read-only
a_list.extend = ['hadz', 'com']

We tried to access the list.extend() method as an attribute which caused the error.

The list.extend() method should be called using parentheses () and not accessed as an attribute.

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a_list = ['bobby']

a_list.extend(['hadz', 'com'])

print(a_list) # 👉️ ['bobby', 'hadz', 'com']

The list.extend() method takes an iterable and extends the list by appending the items from the iterable.

Note that the method returns None, so don't try to store the result of calling it in a variable.

# Conclusion

The Python "AttributeError: 'list' object attribute 'X' is read-only" occurs when you try to access a method as an attribute.

To solve the error, call the method using parentheses () instead of setting it as an attribute using dot . notation.

Here is an example of incorrectly using list.append().

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# 🚨 Incorrect code

a_list = ['bobby', 'hadz', '.']

# ⛔️ AttributeError: 'list' object attribute 'append' is read-only
a_list.append = 'com'

And here is how you would correct the code sample by calling the list.append() method with parentheses.

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# ✅ Correct code
a_list = ['bobby', 'hadz', '.']

a_list.append('com')

a_list.append('xyz')

# ['bobby', 'hadz', '.', 'com', 'xyz']
print(a_list)

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• How to Append a Dictionary to a List in Python
• Append value to List if not already present using Python
• Descriptor 'append' for 'list' objects doesn't apply to a 'str' object
• TypeError: list.append takes exactly one argument (2 given)