object does not support item assignment python class

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Python ‘str’ object does not support item assignment solution

Strings in Python are immutable. This means that they cannot be changed. If you try to change the contents of an existing string, you’re liable to find an error that says something like “‘str’ object does not support item assignment”.

In this guide, we’re going to talk about this common Python error and how it works. We’ll walk through a code snippet with this error present so we can explore how to fix it.

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The problem: ‘str’ object does not support item assignment.

Let’s start by taking a look at our error: Typeerror: ‘str’ object does not support item assignment.

This error message tells us that a string object (a sequence of characters) cannot be assigned an item. This error is raised when you try to change the value of a string using the assignment operator.

The most common scenario in which this error is raised is when you try to change a string by its index values . The following code yields the item assignment error:

You cannot change the character at the index position 0 because strings are immutable.

You should check to see if there are any string methods that you can use to create a modified copy of a string if applicable. You could also use slicing if you want to create a new string based on parts of an old string.

An Example Scenario

We’re going to write a program that checks whether a number is in a string. If a number is in a string, it should be replaced with an empty string. This will remove the number. Our program is below:

This code accepts a username from the user using the input() method . It then loops through every character in the username using a for loop and checks if that character is a number. If it is, we try to replace that character with an empty string. Let’s run our code and see what happens:

Our code has returned an error.

The cause of this error is that we’re trying to assign a string to an index value in “name”:

The Solution

We can solve this error by adding non-numeric characters to a new string. Let’s see how it works:

This code replaces the character at name[c] with an empty string. 

We have created a separate variable called “final_username”. This variable is initially an empty string. If our for loop finds a character that is not a number, that character is added to the end of the “final_username” string. Otherwise, nothing happens. We check to see if a character is a number using the isnumeric() method.

We add a character to the “final_username” string using the addition assignment operator. This operator adds one value to another value. In this case, the operator adds a character to the end of the “final_username” string.

Let’s run our code:

Our code successfully removed all of the numbers from our string. This code works because we are no longer trying to change an existing string. We instead create a new string called “final_username” to which we add all the letter-based characters from our username string.

In Python, strings cannot be modified. You need to create a new string based on the contents of an old one if you want to change a string.

The “‘str’ object does not support item assignment” error tells you that you are trying to modify the value of an existing string.

Now you’re ready to solve this Python error like an expert.

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TypeError: NoneType object does not support item assignment

Last updated: Feb 1, 2023 Reading time · 3 min

# TypeError: NoneType object does not support item assignment

The Python "TypeError: NoneType object does not support item assignment" occurs when we try to perform an item assignment on a None value.

To solve the error, figure out where the variable got assigned a None value and correct the assignment.

Here is an example of how the error occurs.

We tried to assign a value to a variable that stores None .

# Checking if the variable doesn't store None

Use an if statement if you need to check if a variable doesn't store a None value before the assignment.

The if block is only run if the variable doesn't store a None value, otherwise, the else block runs.

# Setting a fallback value if the variable stores None

Alternatively, you can set a fallback value if the variable stores None .

If the variable stores a None value, we set it to an empty dictionary.

# Track down where the variable got assigned a None value

You have to figure out where the variable got assigned a None value in your code and correct the assignment to a list or a dictionary.

The most common sources of None values are:

• Having a function that doesn't return anything (returns None implicitly).
• Explicitly setting a variable to None .
• Assigning a variable to the result of calling a built-in function that doesn't return anything.
• Having a function that only returns a value if a certain condition is met.

# Functions that don't return a value return None

Functions that don't explicitly return a value return None .

You can use the return statement to return a value from a function.

The function now returns a list, so we can safely change the value of a list element using square brackets.

# Many built-in functions return None

Note that there are many built-in functions (e.g. sort() ) that mutate the original object in place and return None .

The sort() method mutates the list in place and returns None , so we shouldn't store the result of calling it into a variable.

To solve the error, remove the assignment.

# A function that returns a value only if a condition is met

Another common cause of the error is having a function that returns a value only if a condition is met.

The if statement in the get_list function is only run if the passed-in argument has a length greater than 3 .

To solve the error, you either have to check if the function didn't return None or return a default value if the condition is not met.

Now the function is guaranteed to return a value regardless if the condition is met.

# Additional Resources

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

• How to Return a default value if None in Python
• Why does my function print None in Python [Solved]
• Check if a Variable is or is not None in Python
• Convert None to Empty string or an Integer in Python
• How to Convert JSON NULL values to None using Python
• Join multiple Strings with possibly None values in Python
• Why does list.reverse() return None in Python

Borislav Hadzhiev

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