How to fix “Unexpected Keyword Argument” in Python

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An “Unexpected Keyword Argument” error occurs in Python when a function is called with a keyword argument that is not recognized by the function’s signature. This can happen if there is a typo in the keyword argument name, or if a keyword argument is used that hasn’t been defined in the function. The error message itself will point out which argument is causing the issue, making the debugging process somewhat more straightforward.

TypeError: function() got an unexpected keyword argument 'custom_argument'

It is always the best way to replicate the issue to understand things better and it helps us to find the most efficient way to resolve the issue

Replicating the ‘Unexpected Keyword Argument’ Error

Create a sample function, Let’s say, A function to greet you based on the name that is shared as an input.

def greet_user(first_name, last_name):
    print(f"Hello, {first_name} {last_name}!")

The above function expects two arguments: first_name and last_name. When called correctly, it greets the user by their full name. However, if you mistakenly call it with an unrecognized keyword argument then you will able to see the error

greet_user(first_name="Fire Lord", middle_name="Ozai")

Output:

    greet_user(first_name="Fire Lord", middle_name="Ozai")
TypeError: greet_user() got an unexpected keyword argument 'middle_name'

Process finished with exit code 1

The above sample code will give you the “Unexpected Keyword Argument” error because greet_user does not expect a middle_name argument. It’s unable to understand the argument you are passing along with the function and the error is pretty straightforward, Saying I don’t know the argument 🙂

Resolution

To resolve the above-simulated ERROR, We need to understand that the required arguments are all needed by the function greet_user

Basically, greet_user function required argument (first_name, last_name). Providing the exact argument will resolve the issue

Example:

greet_user(first_name="Fire Lord", last_name="Ozai")

Output:

Hello, Fire Lord Ozai!

Process finished with exit code 0

Common Causes of ‘Unexpected Keyword Argument’ Errors

Mismatched Function Parameters

One prominent cause of such errors occurs when a function’s parameters do not align with the arguments supplied by the coder. When the function expects a certain parameter and the caller passes a different name as a keyword argument, Python throws an unexpected keyword argument error. It is essential to ensure that the names of the keyword arguments in the function call exactly match the parameter names in the function definition.

Incorrect Function Call Syntax

Analyzing the syntax used in calling a function can also reveal mistakes leading to the error. If a developer includes a keyword argument for a parameter that is not anticipated by the function or mistakenly types the name of a correctly intended keyword argument, the incorrect syntax will trigger the error. Scrutiny of the called function’s signature can prevent such mishaps.

Using Outdated Function Definitions

Lastly, relying on outdated function definitions can result in this error. If a function’s definition has been modified and the codebase still contains calls to the old signature with now-irrelevant keyword arguments, those calls will lead to the error message. Regularly updating references to functions after changes in their definitions ensures consistency and prevents such errors.

By understanding these common causes, developers can swiftly resolve unexpected keyword argument issues and maintain a smooth coding experience.

Strategies for Error Handling and Prevention

Handling an ‘Unexpected Keyword Argument’ error involves strategies that ensure robust function calls and error management in Python code. You must take particular care in how functions are defined, how exceptions are handled, and how keyword arguments are validated before a function is called.

Proper Use of Function Definitions

In defining functions, one must be explicit about the expected arguments. This means using **kwargs sparingly, reserving its use for when a function genuinely requires flexibility. A clear function definition might prevent an ‘Unexpected Keyword Argument’ error by restricting the keywords that can be passed to it and avoiding ambiguity.

Error Handling Using Try-Except Blocks

One can handle exceptions by wrapping function calls in a try-except block. When a function call raises an ‘Unexpected Keyword Argument’ exception, a try-except block can catch it, allowing the program to continue or to provide a more informative message to the user. This strategy does not fix the error, but it allows for more graceful failure and potential logging for debugging purposes.

Example:

    
def greet_user(first_name, last_name):

try:
        # Attempt to call the function with provided keyword arguments   
    print(f"Hello, {first_name} {last_name}!")
    
except TypeError as e:
     # Handle the case where an unexpected keyword argument is passed
     print(f"Error in function call: {e}")

Validating Keyword Arguments Before Function Calls

Before making a function call, keyword arguments should be validated. This can involve checking the type and presence of required keywords and ensuring they conform to expectations. By pre-validating kwargs, one may avoid an ‘Unexpected Keyword Argument’ exception, making code more predictable and less prone to runtime errors. This proactive approach simplifies identifying issues during development, reducing the need for extensive debugging post-deployment.

Conclusion

While errors can be frustrating, they are also learning opportunities. The “Unexpected Keyword Argument” error is no exception. It helps you to write cleaner, more accurate code and encourages a deeper dive into the documentation of the functions they use. As discussed in this article, try recreating the problem and would be of great understanding and help to solve the problem efficiently

Happy Learning!!

Jerry Richard
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