Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an array nums of integers, return the length of the longest arithmetic subsequence in nums.
Note that:

A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.
A sequence seq is arithmetic if seq[i + 1] - seq[i] are all the same value (for 0 <= i < seq.length - 1).

 
Please complete the following python code precisely:
```python
class Solution:
    def longestArithSeqLength(self, nums: List[int]) -> int:
```