How to fix UnboundLocalError: local variable 'x' referenced before assignment in Python
by Nathan Sebhastian
Posted on May 26, 2023
Reading time: 2 minutes
One error you might encounter when running Python code is:
This error commonly occurs when you reference a variable inside a function without first assigning it a value.
You could also see this error when you forget to pass the variable as an argument to your function.
Let me show you an example that causes this error and how I fix it in practice.
How to reproduce this error
Suppose you have a variable called name declared in your Python code as follows:
Next, you created a function that uses the name variable as shown below:
When you execute the code above, you’ll get this error:
This error occurs because you both assign and reference a variable called name inside the function.
Python thinks you’re trying to assign the local variable name to name , which is not the case here because the original name variable we declared is a global variable.
How to fix this error
To resolve this error, you can change the variable’s name inside the function to something else. For example, name_with_title should work:
As an alternative, you can specify a name parameter in the greet() function to indicate that you require a variable to be passed to the function.
When calling the function, you need to pass a variable as follows:
This code allows Python to know that you intend to use the name variable which is passed as an argument to the function as part of the newly declared name variable.
Still, I would say that you need to use a different name when declaring a variable inside the function. Using the same name might confuse you in the future.
Here’s the best solution to the error:
Now it’s clear that we’re using the name variable given to the function as part of the value assigned to name_with_title . Way to go!
The UnboundLocalError: local variable 'x' referenced before assignment occurs when you reference a variable inside a function before declaring that variable.
To resolve this error, you need to use a different variable name when referencing the existing variable, or you can also specify a parameter for the function.
I hope this tutorial is useful. See you in other tutorials.
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Top 2 Methods to Solve the ‘Local Variable Referenced Before Assignment’ Error in Python
Table of contents.
When working with Python, encountering the UnboundLocalError can be quite common, especially when dealing with variables that you intend to access globally within a function. This error typically occurs when a variable is referenced before it has been assigned a value within the local scope.
The Problem: Local Variable Referenced Before Assignment
Consider the following example:
Running the code above yields the error:
The critical point here is whether the variable test1 is recognized as global or local. In this case, Python reinterprets test1 as a local variable due to the attempted modification with += , which leads to confusion when it’s referenced before being assigned any value in the local scope.
So how can you resolve this issue effectively without passing test1 as an argument into test_func ? Let’s explore two main methods to approach this.
Method 1: Avoiding Globals
The best practice suggests minimizing the use of global variables. Instead of modifying a global variable directly, consider passing the variable to a function. Here’s how you could rewrite the example to avoid using a global variable entirely:
In this example, test_func takes a parameter x , performs the operation, and returns the modified value, allowing us to keep the variable scope clean.
Method 2: Declaring a Variable as Global
If modifying a global variable within a function is necessary, use the global keyword. Here’s how you can clarify that test1 should be treated as a global variable within test_func :
By using global test1 , you inform Python of your intention to operate on the global instance of test1 , thus eliminating the UnboundLocalError .
Further Alternatives
While the two methods outlined above are the most straightforward solutions, you can also consider using classes to encapsulate your variables and methods, managing state more formally through object-oriented programming. Here’s a simple example:
This alternative approach provides a structured way to manage your variables, improving code readability and maintainability.
FAQs on Top 2 Methods to Solve the ‘Local Variable Referenced Before Assignment’ Error in Python
Q: what is unboundlocalerror in python, q: how can i avoid using global variables in python, q: does using the global keyword affect performance, q: what are the best practices for variable scope in python.
For additional resources on Python programming, you might find W3Schools Python Tutorials and Geeks for Geeks Python Programming useful.
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