Fix TypeError: 'builtin_function_or_method' Not Subscriptable

Python developers often encounter the TypeError: 'builtin_function_or_method' object is not subscriptable. This error occurs when trying to use square brackets on a built-in function or method. Let's explore why it happens and how to fix it.

What Causes This Error?

The error occurs when you mistakenly treat a function or method as if it were a sequence or mapping. In Python, only objects like lists, dictionaries, or tuples support indexing with [].

Here's a common example that triggers this error:

# Incorrect usage causing the error
my_list = [1, 2, 3]
print(my_list.append[0])  # Trying to subscript the append method

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'builtin_function_or_method' object is not subscriptable

Common Scenarios and Fixes

1. Mistaking Parentheses for Square Brackets

This often happens when calling a function but using [] instead of ().

# Wrong way
result = len[1, 2, 3]  # Using [] instead of ()

# Correct way
result = len([1, 2, 3])  # Proper function call with ()

2. Incorrect Method Access

Another common mistake is trying to access a method as if it were an attribute.

my_string = "hello"
# Wrong way
char = my_string.upper[0]  # Trying to subscript upper()

# Correct way
char = my_string.upper()[0]  # First call upper(), then index

3. Confusing Functions With Containers

Sometimes developers confuse functions that return sequences with the sequences themselves.

# Wrong way
numbers = range[10]  # range is a function, not a list

# Correct way
numbers = list(range(10))  # Convert range object to list first

How To Debug This Error

When you see this error, follow these steps:

1. Check where you're using square brackets []

2. Verify if the preceding object is a function or method

3. Replace [] with () if you meant to call the function

4. If you need indexing, ensure the object supports it

Prevention Tips

To avoid this error in the future:

- Always use () for function calls

- Remember that methods need parentheses to execute

- Check an object's type with type() if unsure

- Use proper variable names to avoid confusion

Related Errors

This error is similar to other Python type errors. For example, you might encounter ModuleNotFoundError when importing modules incorrectly. Understanding these errors helps in debugging.

Conclusion

The TypeError: 'builtin_function_or_method' object is not subscriptable is a common mistake. It happens when trying to use indexing on a function or method. The solution is simple: use parentheses for function calls and square brackets only for indexable objects.

By understanding this error, you'll write better Python code. Remember to always check your syntax when using functions and methods. For more Python error solutions, check our guide on ModuleNotFoundError.