"TypeError: 'type' object is not subscriptable" in a function signature

user_14122344 0
Viewed 21166

Why am I receiving this error when I run this code?

Traceback (most recent call last):                                                                                                                                                  
  File "main.py", line 13, in <module>                                                                                                                                              
    def twoSum(self, nums: list[int], target: int) -> list[int]:                                                                                                                    
TypeError: 'type' object is not subscriptable

nums = [4,5,6,7,8,9]
target = 13

def twoSum(self, nums: list[int], target: int) -> list[int]:
        dictionary = {}
        answer = []
 
        for i in range(len(nums)):
            secondNumber = target-nums[i]
            if(secondNumber in dictionary.keys()):
                secondIndex = nums.index(secondNumber)
                if(i != secondIndex):
                    return sorted([i, secondIndex])
                
            dictionary.update({nums[i]: i})

print(twoSum(nums, target))
typeerror type-hinting python-3.x list python
3 Answers

The following answer only applies to Python < 3.9

The expression list[int] is attempting to subscript the object list, which is a class. Class objects are of the type of their metaclass, which is type in this case. Since type does not define a __getitem__ method, you can't do list[...].

To do this correctly, you need to import typing.List and use that instead of the built-in list in your type hints:

from typing import List

...


def twoSum(self, nums: List[int], target: int) -> List[int]:

If you want to avoid the extra import, you can simplify the type hints to exclude generics:

def twoSum(self, nums: list, target: int) -> list:

Alternatively, you can get rid of type hinting completely:

def twoSum(self, nums, target):
user_29887300

The answer given above by "Mad Physicist" works, but this page on new features in 3.9 suggests that "list[int]" should also work.

https://docs.python.org/3/whatsnew/3.9.html

But it doesn't work for me. Maybe mypy doesn't yet support this feature of 3.9.

user_20054710

The “TypeError: ‘type’ object is not subscriptable” error is raised when you try to access an object using indexing whose data type is “type”. To solve this error, ensure you only try to access iterable objects, like tuples and strings, using indexing.

user_46687510
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