Errors are an inevitable part of programming. While they may seem frustrating, they serve as an opportunity to debug and deepen your understanding of how programming languages like Python work. One such common error is the typeerror: ‘builtin_function_or_method’ object is not subscriptable which often confuses even experienced developers. This article will explore the causes of this error, how to fix it, and offer best practices to avoid encountering it in the future.
What Does “typeerror: ‘builtin_function_or_method’ object is not subscriptable” Mean?
In Python, a subscriptable object is one that supports indexing operations, such as lists, tuples, dictionaries, or strings. These objects allow you to use square brackets ([]) to access specific elements. For example:
However, a typeerror: ‘builtin_function_or_method’ object is not subscriptable is a Python object representing functions or methods that are part of Python’s built-in features, like len, append, or strip. These functions are not subscriptable, as they do not contain individual elements that can be accessed via an index.
When you attempt to subscript a function or method, Python raises the TypeError. For example:
Common Scenarios That Trigger the Error
This error typically occurs when a developer mistakenly treats a function or method as if it were a subscriptable object. Here are the most common scenarios:
1. Misusing Built-in Functions
If you assign a built-in function, such as len, list, or str, to a variable and then attempt to use it as a list or string, the error is raised. For example:
2. Forgetting Parentheses When Calling a Function
Another frequent mistake is forgetting to include parentheses when calling a function. Without parentheses, Python treats the function itself as an object, rather than executing it. For example:
Here, my_list.append refers to the append method itself, which is not subscriptable.
3. Overriding Built-in Function Names
If you inadvertently use a built-in function name as a variable name, you may cause unexpected behavior. For instance:
4. Treating Non-Subscriptable Objects as Subscriptable
Beyond functions and methods, the error can also arise if you mistakenly treat other non-subscriptable objects, such as integers or floats, as subscriptable:
How to Fix the Error
Resolving the error requires understanding why it occurred and making the necessary corrections. Below are specific fixes for common causes:
1. Add Parentheses When Calling Functions
Always ensure that you use parentheses when calling a function. For example:
2. Avoid Overwriting Built-in Function Names
Avoid using built-in function names like list, len, or str as variable names:
3. Debugging Using type()
When unsure about the type of an object, use the type() function to verify whether it is subscriptable. For example:
4. Check for Accidental Variable Reassignment
Trace back your code to ensure no unintended variable assignments have overridden built-in functions:
Best Practices to Avoid the Error
Adopting these coding practices can help prevent the TypeError:
1. Use Descriptive Variable Names
Avoid naming variables after built-in functions or methods. For instance, instead of using list or str, use names like my_list or my_string.
2. Understand Object Types
Be mindful of the types of objects you’re working with. Functions and methods are callable, but they are not iterable or subscriptable.
3. Test Small Code Segments
Testing smaller sections of code allows you to identify and fix errors early, reducing the likelihood of encountering such issues in larger programs.
4. Leverage IDE Warnings
Modern IDEs (Integrated Development Environments) like PyCharm, VSCode, or Jupyter Notebook can highlight potential errors, such as calling a method without parentheses or reassigning built-in functions.
5. Review the Official Documentation
Reading Python’s official documentation about built-in functions and methods will help you understand their correct usage.
Real-World Example
Below is an example program where this error could occur, along with the corrected version:
Incorrect Code
Correct Code
FAQs
1. What is a typeerror: ‘builtin_function_or_method’ object is not subscriptable?
A typeerror: ‘builtin_function_or_method’ object is not subscriptable is one that supports indexing or slicing using square brackets ([]). Examples include lists, strings, tuples, and dictionaries.
2. Why is a function or method not typeerror: ‘builtin_function_or_method’ object is not subscriptable?
Functions and methods are not collections of elements; they are callable objects. As such, you cannot access elements within them using an index.
3. How can I check if an typeerror: ‘builtin_function_or_method’ object is not subscriptable?
You can check if an typeerror: ‘builtin_function_or_method’ object is not subscriptable by using the collections.abc.Sequence class from Python’s collections module:
4. Can I fix this error without changing my code?
No, this error indicates a fundamental misunderstanding of the object’s type and behavior. You must revise your code to correctly handle the object in question.
5. What happens if I accidentally overwrite a built-in function?
Overwriting a built-in function can lead to unexpected behavior. You can restore the original function by restarting your Python session or re-importing the module it belongs to.
Conclusion
The typeerror: ‘builtin_function_or_method’ object is not subscriptable arises from treating functions or methods as subscriptable objects. By understanding how Python handles functions, methods, and indexing, you can effectively debug and prevent this error in your code. Remember to use clear variable names, verify object types, and always include parentheses when calling functions. Following these practices will not only save you time debugging but also make your code more robust and maintainable.
