Solving Python Error: Object of Type Builtin Is Not Subsettable

The error “object of type ‘builtin’ is not subsettable” occurs when you try to access or modify elements of a built-in object in a way that is not allowed. This typically happens when you attempt to use indexing or slicing on an object that doesn’t support these operations, such as a function or a non-sequence type.

To fix this error, ensure that you are working with a sequence type (like a list or tuple) or use appropriate methods to access the object’s properties.

Common Causes

Here are some common scenarios that lead to the error ‘object of type builtin is not subsettable‘:

Using Square Brackets on Functions:
- Attempting to use square brackets [] to index a function instead of calling it with parentheses (). For example:
```
def my_function(x):
    return x * 2
my_function[5]  # Raises the error
```
- Correct usage:
```
my_function(5)  # Correct
```
Misinterpreting Built-in Functions as Data Structures:
- Trying to subset built-in functions like len, sum, etc., as if they were lists or dictionaries.
```
len[0]  # Raises the error
```
Incorrectly Accessing Attributes:
- Attempting to access non-existent attributes of built-in objects without using the correct methods.
```
getattr(len, 'non_existent_attribute')  # Raises the error
```
Confusing Built-in Types with Custom Objects:
- Mistaking built-in types (like int, str, etc.) for custom objects that support subsetting.
```
int[0]  # Raises the error
```

These scenarios typically arise from misunderstanding the nature of built-in functions and objects in Python. If you encounter this error, double-check whether you’re treating a function or built-in type as a subsettable object.

Identifying the Error

The error “object of type ‘builtin’ is not subsettable” occurs when you try to subset a built-in object in Python, such as a function, using square brackets []. Here’s how to identify and debug this error:

Typical Error Message

TypeError: 'builtin_function_or_method' object is not subscriptable

Debugging Steps

Identify the Object: Check the object you are trying to subset. Ensure it’s not a built-in function or method.
```
print(type(your_object))
```
Check for Misnamed Variables: Ensure you haven’t named a variable the same as a built-in function.
```
list = [1, 2, 3]  # Correct
list[0]  # Accessing first element
```

Correct Subsetting: Use parentheses () to call functions, not square brackets [].

def my_function():
    return [1, 2, 3]

result = my_function()  # Correct
print(result[0])  # Accessing first element

Convert to Sequence: If needed, convert the object to a list or tuple.
```
my_tuple = tuple(my_list)
print(my_tuple[0])
```

By following these steps, you can identify and fix the “object of type ‘builtin’ is not subsettable” error in your code.

Solution 1: Correct Function Usage

To resolve the error “object of type ‘builtin’ is not subsettable,” ensure you are using functions and methods correctly. This error typically occurs when you try to index or subset a built-in function or method, which is not allowed.

Solution:

Identify the Function or Method: Ensure you are not mistakenly treating a function or method as a subscriptable object (like a list or dictionary).
Use Parentheses for Function Calls: Always use parentheses () to call functions or methods. For example, if you have a function my_function, call it with my_function() instead of my_function[].
Check Variable Names: Avoid naming variables the same as built-in functions or methods to prevent confusion. For instance, do not name a variable list or dict.

Here’s an example:

# Incorrect usage
print(len[5])  # Raises the error

# Correct usage
print(len([1, 2, 3, 4, 5]))  # Outputs: 5

By ensuring you call functions and methods correctly with parentheses and avoiding naming conflicts, you can prevent this error.

Solution 2: Using getattr() Function

To resolve the error ‘object of type builtin is not subsettable’ using the getattr() function, follow these steps:

Identify the Object and Attribute: Determine the object and the attribute you want to access.
Use getattr(): Replace the subscript notation (e.g., object['attribute']) with getattr(object, 'attribute', default_value).

Here’s a quick example:

class MyClass:
    def __init__(self):
        self.my_attr = 'value'

obj = MyClass()

# Incorrect way that causes the error
# value = obj['my_attr']  # This will raise the error

# Correct way using getattr()
value = getattr(obj, 'my_attr', None)
print(value)  # Output: value

In this example, getattr(obj, 'my_attr', None) safely retrieves the attribute my_attr from obj without causing the error.

Solution 3: Using dir() Function

The dir() function can help identify the attributes and methods of an object. When you encounter the error ‘object of type builtin is not subsettable’, it often means you’re trying to use indexing on a built-in function or method, which isn’t allowed.

By using dir(), you can inspect the object to understand its structure and see what attributes or methods are available. This helps you avoid incorrect operations like subsetting on non-subsettable objects.

For example:

print(dir(some_builtin_object))

This will list all the valid attributes and methods, guiding you to use the object correctly and avoid the error.

To Solve the Error ‘Object of Type Builtin is Not Subsettable’

Ensure you are not mistakenly treating a function or method as a subscriptable object.

Use parentheses for function calls, check variable names to avoid conflicts with built-in functions or methods, and identify the object and attribute you want to access.

Use the getattr() function to safely retrieve attributes from objects without causing the error.

The dir() function can also help inspect an object’s structure and identify its valid attributes and methods.

By following these steps and tips, you can resolve the error and write more accurate code.

Sep 19, 2024
Roderick Webb
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